Hey guys, I've milled around this site for quite some time now while debating on if I wanted to make the dive into a Z28 or not. After reading so many good things, I decided to take the jump and bought me a '92 Z28 25th with the 350ci. Gorgeous car, but she's been giving me a few issues that are starting to try my nerves.

Long story short, I'm the 3rd owner. The guy I bought it from had it sitting in a storage unit for 6 months before I came to look at it. When I first saw it, batt was dead (expectedly), and after getting a charge, she wouldn't crank. Brought it to a mech, had the fuel lines cleaned and a new pump put in under warranty. They supposedly checked through it and said everything looked good. She ran fine after the install, so I bought her.

The drive home, everything was peachy. A little black smoke on first start, but I attributed that to her sitting for so long and burning off all the crap stuck in the engine.

After the 20min drive home, I noticed she smelt like she was running rich, both outside and in the cabin. No smoke, no hesitation, no stalling, just the smell. She has a small hole in the exhaust so I thought maybe that's what it was from. Booked an appt with my personal mech to have him check.

Then yesterday (day 2 of ownership) I went to the store not even a mile away. Started right up, drove fine. At the 1st light I turned the A/C on. She bogged a little but caught back up. Got to the store fine. I was in and out in 15 mins. Got back and she didn't want to crank. Would start, run VERY rough, then die. Did this 3 times before I got her to stay running, and it was definitely a rough run. No visible smoke, but smelt rich as hell and was not a happy camper. I didn't bother trying the A/C, didn't think it'd handle it.

I can't really say what the idle is like since my tach is shot. It zero's out at 3k rpm and at normal idle is around 4.5k. In the parking lot she was jumping around from 5k down to ~3.5k and back. Took Drive fine, but was dying to jump off the brakes (surging). It almost felt like catastrophic misfire. The PO installed a shift kit so she races out of 1st almost instantly which didn't help. It never stalled, but damn near tried to a few times at red lights. When moving, she seemed to keep up, at least she sounded so - I was too busy sweating bullets in the FL heat and hoping I didn't get stuck in the middle of the road to pay attn to the tach.

I called my mech and explained it all, he automatically suggested new plugs / wires which had crossed my mind. He said I may need a new O2 sensor too, but he'd check that before pulling it.

I know this probably sounds pretty common, but does anyone have any other ideas besides new plugs, wires, cap, rotors etc? I don't want to throw parts at it and hope for the best, can't really afford to go that route. If it is a misfire, is trying to jump off the brakes normal when it's surging (almost like I'm holding the brake and flooring it at the same time)? It's very obvious that once she gets up to temp is when all hell breaks loose. Could that be a sign of something other than plugs?

On a different note, when I first drove her, seemed like the brakes were shot. The mech said there may have just been air in the lines and to pump them out and see if it makes a difference. It did somewhat, but they still seem pretty weak. Pads and Rotors are good though. Do these cars just need a little more foot power on the pedal or should I look into flushing the fluid to see if that helps?

I attempted to open the hood while she was parked in my inclined driveway (like I said, PARKED) and once the hood came up the damn thing started to roll away! I'm a little stumped (not to mention embarrassed after having to chase my own car) as to why it's rolling in park. I mean, yeah the hood is heavy as all hell but...........

And finally, what in God's name does a guy gotta do to get the damn horn to work?

Thanks for your help everyone, and sorry for the long post :-)

 

All those things are good maintenance, but if you're strapped for cash...

When it gets warm the computer goes into "closed loop" where the ECM is reading the O2 sensor for air/fuel ratios. Try unplugging the O2 sensor and see what happens. It will throw a code (SERVICE ENGINE SOON light) but I think it will just stay in open loop and run that way. If the problem goes away, you may need to replace the O2 sensor, or it could be something else along the line.

Puffs at startup are very common. It's just valve seals that wear out over the years. Doesnt really hurt anything, just oil drips down into the cylinders when the car sits a while, then you go fire it up and all the oil burns out. It will smell like oil and puff at startup. It doesnt consume very much oil and it doesnt affect much of anything while the car is running (in the vast majority of cases) and it's kind of a pain to fix. So just ignore it, it's fine.

About the brakes... I'd bleed every caliper. I like to do what's called "gravity bleeding" (search if you want) because it's easier and i can do it by myself. Just open the bleeder screw and let it drip for a while and keep filling the open brake fluid resevoir with brake fluid. I'd do this at all four corners and drip a quart or so of brake fluid out. (Just buy a quart, and fill it as you bleed) Or you can just get a friend and do it the old fashioned way, your call. If that doesnt help i would seriously recommend replacing your brake lines. As brake lines get old they get softer. When you mash the pedal, instead of the force of the fluid pushing onto the brake pads, it just makes the brake line balloon up and all your pedal travel gets wasted filling up your brake lines that have become balloons of brake fluid. If thisi s the case they will eventually burst and that's very bad. It's not a hard job, just make sure you put the right brake line on the right side and the left brake line on the left side. Lines will be about $20 per side. You'll need a flare nut wrench for the junction between the hardlines and the rubber line in the fender. After you get done you'll need to bleed it again. If the pads and rotors look fine you shouldn't need to do anything to them. The brake caliper will have a random nut on the back of it with a protrusion on the back. Thats the bleeder screw. Crack it open and let it flow/drip. It will also have a bolt going through the brake line. That bolt (there are two copper washers on each side of the brake line, make sure you get new ones, or at least re-use the old ones) and the nut on the other end of the brake line are all that holds the brake line in (that and a little sliding clip on the strut). The important thing is the hard line's nut - make sure you use a flare nut wrench. Looks like this:



You do NOT want to strip that nut on the hard line. It will make an easy job WAY more complicated than it needs to be. Flare nut wrenches grab onto the nut a lot better and prevent it from stripping.


And remember, at the end of the day, it's a 20 year old car. You're gonna need to learn to get a little greasy under the hood, but you and the car will grow together and it will be a beautiful thing. Otherwise you're gonna go broke paying a mechanic to make the same guesses you'll have to make about what's wrong with the car and then paying for his time and new parts that may or may not fix it. We all have to take stabs in the dark sometimes, but if you're paying someone else to do it for you and you go broke you're gonna end up hating yourself, the car, mechanics, and the world, etc.

 

Hey, thanks. I'm going to change out the plugs and all tomorrow, I'll try the O2 sensor when I'm working on it. Hopefully that's all it is. :-)
Brakes, well that'll have to wait for another day, but many thanks for all the help!

 

Plugs, cap, rotor, wires and all new fluids are the first thing required of a new, 'used' vehicle. The O2 sensor is also a routine replacement item. Troubleshooting any issues with the above items in the 'unknown good' category is pointless.

Part of new fluids is new brake fluid (along with tranny and rear-end).

Don't pay someone to do this routine maintenance stuff. Dive in yourself. There's pride of ownership and pride of accomplishment. I prefer the second.

 

WTF

the brakes are the FIRST thing that you need to make sure are in top order. You are all concerend abotu wanting to feel the kick in the butt from accelleration. Once your done with all that testosterone stuff you still need to STOP. Is your life not worth it? Ask your folks, I bet they would want you to fix the brakes first because they love having you around. have I made my point?

Also, ask any parent if they would rather your engine not run rough or would prefer that you could stop as you are behind their family?

If you've never done brakes, then pay someone. As for this "mechanic" of yours (I doubt he is really is) , go find a new one for everyhting but new wiper blades. If your brakes are not working properly pumping the pedal won't fix it. And, that's not how you bleed out air. The air must go somewhere and if it does, then that's called a leak.

Good grief, for the love of God, fix your brakes and be safe. If your folks or friends don't have knowledge or experience, then PM me. If you really are in orlando, maybe my son at UCF would be willing to give you a crash course on diagnostics and what's what under the hood.

 

My point about the brakes was that they WORK, just not as responsive as, say, a newer car. I guess I was asking if this is normal, or if they should all feel the same.
My mechanic is...a mechanic. ASE certified and all
And there is no Need for Speed going on here, just trying to make my almost perfect Z...perfect.

 

Ha, when I first bought my TA it took me 3 hours to drive the 18 miles home, due to continual overheating and stalling. I knew the car was a basket case before I bought it, but still...

Long long long story short, turned out the first thing I had to fix was everything. Took about 2 years, but I persevered and learned a LOT. Biggggg learning curve, not so much about cars in general, but about thirdgens in particular. If you've been hanging around here any length of time, you'll already know most of the answers are on here by searching.

Also second what Torque said - fix the brakes first! Then give tyres, wheel bearings, and suspension/steering joints and links the once-over. When you're confident it's not about to kill you, move on the the engine issues.

Edit: You beat me with your last post. These cars are known for having pretty poor stock brakes - plenty of ideas on these forums for improvement.

 

LOL "not about to kill you"...
Yeah, I've been a "guest" on here for a few months now, just checking to see what people complain about with their's, what the pro's and con's are...
Luckily for me, the PO had done a lot to restore her. Upgraded suspension, tires, etc etc
I'm going to be tearing it apart later today to see where my problem lies.
Thanks

 

then you definitely misunderstood him. No mechanic will tell you that pumping the pedal on a sealed hydraulic system will bleed the air.

I'm glad that it stops. Who cares how quick it will go. If you can't stop............well, nuff said. We want you here.

 

I bet if you change the rubber brake lines and bleed the brakes it iwll be a night and day difference.

Brakes on these cars ARE bad, but they're only bad in terms of brake fade. They heat up quickly under hard racing and fade. As far as just trying to stop the car, it should be as good as any other car out there - just keep in mind it doesnt have ABS.

 

Haha no no, we must be misunderstanding eachother - MY mechanic wasn't the one to first check the car out. It was at one of those big-box mechanic shops (PB's), and THEY'RE the ones who told me that. Brakes aren't really my thing, never had any problems with them on any other car I've owned, although I use to switch my cars up like no tomorrow once up a forever ago.

And for the "we want you here"

 

This is what I'm going to do, just figure it out and have at it. I remember it not having ABS, John Davis made a note of this when he reviewed it on Motorweek...back in '92.

Ahh the wonders of youtube

 

Count your blessings that it doesnt have ABS. I'm so sick of dealing with old cars and ABS problems. Hell new cars have tons of ABS problems. And for racing ABS is a hindrance, not an advantage.

I doubt 20 year old ABS systems would be working that well these days in these cars.

 

Okay, so update.
Brake lines are like mush. Time for new ones. Thank you, Vortex, for leading me in the right direction
Now the new problem persists. Changed out the plugs (w/ AC Delco's) & plug wires. Found out that 5 and 8 weren't firing at all which explains a lot. After I got it all put back together, turned the key and she fired right up...for about a minute. Then died. And refused to restart.
She's definitely getting fuel, so that's not the problem. I don't think there's any spark when I crank it. So this leads to my next question - Is it definitely the Distributor Cap? I thought long and hard about just buying it and throwing it on in one shot today, but didn't want to just dump a whole mess of parts in it and wish for the best.
One of the plug wires was worn to s**t when I removed it...I'm wondering if it could have caused an arc in the Cap...
Any other ideas?
I know it's probably something minute that I'm completely missing.

Thanks for al the help

 

I always like to replace the ignition module when it starts acting flaky and you cant track it down. Two reasons - 1. It's cheap. 2. If it doesn't fix it, you have a spare laying around. They often fail intermittently and will leave you stranded. So even if it doesn't fix it, it WILL fail eventually, throw your spare in and get home. Get a stock replacement. Ac delco/ Borg Warner/ Delphi. Dont touch the Accel/MSD/Mallory ****.

 

I'll look into that
What are the odds of it flaking out RIGHT AFTER I change the plugs?

 

Check the cap is a)seated properly and b) that the center 'button' inside the cap is still there! I had a coil blow that right out...
Check all the vacuum lines (really, replace them all anyway)...these cause all sorts of problems. Check the MAP sensor too. One thing that should also be replaced as soon as you can if you are not sure how old it is is the catalytic convertor. Not long after I bought my 91 Camaro, my car overheated and melted the EGR valve. Turned out the cat was so shot that the material inside was all rusted and loose and on startup it blew to the back of the cat and clogged it, causing the exhaust to superheat and the engine to choke... real pain in the butt.

 

Low.

But you said it was running like crap warm before too... could be the O2 sensor, could be the module. Could be an umber of things. Odds are low. depends on the symptoms. Ignition modules usually fail like this: It runs okay, and then suddenly it gets warm and doesnt run at all and you get no spark, and you come back later and it runs okay again.

 

Superheat...no fun.
I'm thinking I just made a stupid mistake of not replacing the cap when I did everything else. In all honesty I don't remember if the "button" is still there, or at least "there enough". I'd check it now, but the rain has commeth.
MAP sensor...that would make sense for the crap run before I switched out the plugs. Now, I'm the first to admit I'm not an expert here - but wouldn't the MAP affect fuel flow? I don't think I have a fuel delivery problem, it ran rich before the change, and ran rich after. After trying to crank it to no avail, I could smell fuel.
Then again, you probably know much more than I do

 

I threw a new O2 sensor in it today too, sorry I forgot to mention.
"...come back later and it runs okay again..." ---> EXACTLY!
I'll be doing that tomorrow too

 

InfernalVortex, I owe you big time.
First thing this morning, went down and bought a new ICM. Threw it in and voila - good as new. She doesn't even run as rich as she was.
$50 piece caused $1000 worth of headaches. lol

My Raven is ready to fly once again.

 

What brand module did you get? $50 sounds kind of high unless you got a "performance" variant. My experience with the fancy ones has been very bad. I always go with direct factory replacement modules. But you'll know what to look for if it comes back in a year or so.

 

It's a Duralast, from Autozone...
Just got back from taking her around town for a bit. I noticed it has a rather unsteady idle now? (Fluctuates a few '00 RMP's when in Park)
Hmmm...

 

Duralast is probably fine.

unsteady idle - check vacuum lines. Is the SES light on?

Your ignition should be tip top - new plugs, wires, rotors, cap, and module, right?

Is it "loping" (misfiring) or just surging up and down? Do a search for surging idle. Surging idle usually means a bad sensor or a vacuum leak. Your O2 sensor is new, too, yes?

Try
1. Moving around the heater/AC controls
2. Make sure your vac lines to the MAP sensor and brake booster look good and are plugged into the ... wherever they need to go on a TPI.
3. take note of whether it does it more or less when it's hot or cold

You dont have a MAF sensor, so that rules that out. (The MAP sensor basically replaces it, and MAF sensors are WEAAAAY more expensive than MAP sensors)

Believe it or not you're definitely narrowing things down and improving it. A lot of the little wear and tear issues on these cars - you're handling and it should be good for a long time once you get it all buttoned up.

 

No SES light. Yes, new, new, and new.
From what I see, just surging. I drove it for about 1/2hr with no problems. A/C on and all. Got it home and turned off the A/C (my SOP with all my cars) before shutting it down and noticed the RMP's rise a little (attributed it to less drag from the compressor). They leveled back out, but started doing the dance.
My tach is shot, but from feeling I'm guessing it's going from ~1000 to ~1300 and back.
I'll search for the tread now, thanks.

 

Heres a good thread:

https://www.thirdgen.org/forums/tech...idle-dies.html

This guy's issue was ECM. I wouldnt assume thats your issue at all. Good thing is you can get these parts cheap at all kinds of places, no need to buy new.

The HVAC controls (that control where the air is directed, which vents, defrost, etc) are vacuum controlled, and are often sources of air leaks. The selectors get old and wear out and the engine can pull in air from the cabin actually - this reduced amount of vacuum wreaks havoc with the sensors. So play with the vent selections and see if it does anything weird. If it's easy to get to the port where the vent vacuum is sourcd, you can just pull the line and put a cap on it. I would probably disconnect every vacuum line and put a cap on it and see how it idles (with the exception of the line to the MAP sensor), but I already have a bunch of vacuum caps and on my car I have all of 2 vacuum lines to deal with. Just dont go driving around like that because you will not have power brakes. Otherwise you can just toss a vacuum gauge on it and see what your vacuum measurement is and that iwll give you a clue also.

You're right that the RPMs going up is likely because of the A/C clutch disengaging. Less drag on the engine.

The idle surging thing is one of those hard to diagnose, could be anything, you can throw parts at it for years problems. You just have to be smart about it and pay attention to how and when it does it.

 

Yep, threw a new O2 sensor at it yesterday.
I've taken it out a few times today, once right after replacing the ICM, and once right before my 1st post. It behaved fine on the first drive, but then again, I didn't take it out for long. The second drive was longer and allowed it to run up to temp. It wasn't until running temp and was in park that I truly noticed it. It MAY have been doing it while on the road, but my exhaust system vibrates so much, I wouldn't have been able to differentiate the sound / feeling. However, no lag on pickup, no hesitation.
I'll try playing with the HVAC controls to see if it makes any difference.

Also, on a slightly similar note - is there a "standard length of time" needed for it to fire? I had expected the crank time to decrease after new plugs...but it didn't. Not too worried about it, just curious?

 

So after playing with the HVAC I didn't notice much different. When I'd switch between hot / cold the engine would dip a LITTLE then catch back up...but all my cars have done this so I don't think this is out of the ordinary.
Now what? lol

 

my thirdgen has been one of the strongest and most reliable cars i have ever owned, once you get past the sensor issues it should run great. afterall any car after 20 years time is going to need maintenence. just think, do you think chevy would have used an unreliable motor in its top car the corvette. that is basically the same engine as the camaro anyway.

 

why don't you check for codes and then test your fuel injectors for ohms. that would be a great start.

 

No codes except 12. I cleaned out the injectors at plug replacement - do you think that would make a difference as far as ohms at all?

 

no

 

If the car is otherwise drivable aside from the surging idle, you're just gonna have to figure out over time what it is.

Dont get discouraged, just over time take care of little things as you can. You've replaced all the big stuff already, and you dont have an expensive MAF sensor to replace. Most of hte other parts that could cause a surging idle condition are cheap with the exception of the injectors, but I've never noticed any sort of connection between bad injectors and surging idle conditions, so I'm not sure that route will yield anything meaningful, but anything is possible when it comes to 20 year old fuel injection systems.

I dont know much about the nitty gritty of TPI's since I've never owned a TPI a car, but look into making sure the EGR valve is clean (it's probably fine since it's not throwing a code, but they cause this too so it's worth checking), and go and try and reset the idle air control (IAC) properly.

Beyond that the things that I would look into are, in no particular order:
Coolant Temp Sensor (CTS)
Manifold Absolute Pressure sensor (MAP)
Throttle Position Sensor (TPS)
Electronic Control Module (ECM)
Fuel Pressure
Fuel filter

A lot of the things that can cause it, you've already replaced with new parts, you'll get it!

Basically what it is, is the computer getting an anomalous signal or a bad reading from something, and it doesn't know it's bad. So it compensates by changing air/fuel/spark/whatever to bring the anomalous reading back into the ideal range. As it does that, another sensor's readings go out of the ideal range, and the ECM sees that too, and adjusts the other way. So you get basically an endless feedback loop as the ECM is trying to make it work right. This is why it's difficult to track down what's causing it.

 

I recently purchased a '91 Z28 5/7 TPI car. had been sitting in the PO garage for 5 1/2 years. i trailered it from there to me personal mechanics shop for a once over. We did the usual plug, cap, rotor, wires, etc. Ended up changing fuel pump, tank, new fuel rail seals, injector seals, etc. in the end, ran into the same idleing issues, etc. narrowed it down to TPS sensor.$19 part at autozone. Just had to tune the TOS sensor in with Ohms meter. IDled smooth after that, moie power and better response.

 

Do a compression test and start checking for mechanical problems

 

What part of FL are you in???

 

You can try to clean the Idle Speed Motor. They get gunked up and will stick at certain openings, causing erratic idle. May not be it but pulling it out and cleaning it with carburetor cleaner is free and probably needed anyway.

 

I seriously doubt serious mechanical problems will cause a surging idle and it run fine th rest of the time. Serious mechanical problems are things like wiped cam lobes, massive blow by smoke all the time, and knocking rods. 95 percent likely this is electronic.

 

A cracked or warp head or a head gasket fail will cause a surging idle and depending on where it blew or cracked may drive fine most of the time.

 

Will likely have several other symptoms too. Coolant/Oil mixing, steam out the exhaust, noises, lack of power.

 

Orlando.

 

I don't think this is the issue, at least I hope not. I always check for "unnatural" exhaust (water, steam etc), oil isn't milky. Noises? Well yeah, but can't really pinpoint where they're coming from...

 

don't forget the street nationals are coming halloween weekend

 

Certain noise is just... noise. Others are worth worrying about. If it's worth worrying about you'll know it. Dont get too paranoid.

Check on the idle air control, EGR valve, and then start replacing the sensors you have left. There aren't too many. And most mechanics these days dont really know how to handle our cars. Our fuel injection systems are so old and primitive that most people who work on fuel injection work on modern EFI, and most people who work on old school stuff wont know how to handle it either.

 

o well if you were in the western part of the panhandle i would of rode out and helped you out or invite you to come over and use my garage