Ok here goes. Search turned up only what I've already replaced:
MAP Sensor
O2 Sensor
IAC
TPS
Air Filter
Fuel Filter
Recent Tune-Up
coolant temp sensor and switch
seafoam gets run through the PCV valve yearly.

what it does:
When car is warmed up and idling at a stop light in Drive the idle is just crappy. I can hear the fuel bumps hum going up and down with the rpm's of the car. It's subtle but I'm worried it might end up something big that strands me. The RPM gauge goes from about 800 to 400 continuously. Seems like it just might die at times. ** If I slip it into neutral it's fine. Idle's smooth as glass.

What I think it is:
Either fuel injectors or possibly something with the transmission like maybe the torque converter or something? It seems to be REALLY pulling against the breaks like I'm still on the gas or something.

 

This is going to sound incredibly retarded, but what kind of shape are your vac lines in? I'd especially check the rubber ends of the one going to the MAP sensor and the intake nipple on the back of the upper plenum. Is it possible that the check valve on the brake booster, the line connected to it and the engine, the line going to the evap can, and the line going to the cruise module/vacuum tank ball (and the ball itself) are leaking? Also check the connections on the PCV valve and intake, the breather nipple in the pass side valve cover, and where the breather pipe attaches to the intake bellows. Any looseness is trouble, along with cracking/deterioration.

 

I've replaced all of my vacuum lines with silicone ones, but I will look for a leak. Thanks for the tip. - Nate

 

The reason I said to start there is because it's cheap (free), easy, and it don't take long. Plus, my 2.8 was so bad with this that it would completely stall when I would come to a stop when hot. I ended up power braking most of the time just to keep the engine running so I wouldn't have to get out and shoot it up with starting fluid to get going again. This sounds kind of like what I went through all that long ago.
If you don't have any leaks, I can also tell you how to test to see if your MAP has the proper signal.

 

No Vacuum leaks, I'm thinking maybe it's my accel ignition coil? It seemed to run smoother without it. Also, I have no codes but it smells a little rich. (yes I know how to check my codes )

 

check the timing with a timing gun easyer to see if there is slop in the chain. loose/warn out chains make these cars run like poo.

 

Let me just say this about my Accel coil: It's a $48 paperweight now. Has been for quite some time... I always find it AFTER I go through and throw out the rest of the garbage in the garage.

The coils aren't meant for on-the-road driving, as they overheat and fry their internal wiring insulation very easily. Try switching back to your stock coil (just unplug the Accel and set the old one on top of it, yes there is room). Your car smells rich because, I'm willing to bet, the Accel is past it's service life and it's giving out weak spark.

 

Thanks I'll give it a try. The old one is stock though, so how long could I really expect it to continue functioning?

ensrpb - I don't have a timing gun and I don't know how to use one. I'm into buying a new chain, how hard is it to replace?

Could this problem be my stock injectors? I have no idea how to check them, but that would throw a code right?

 

New stock coils are cheap. If you're going to do the chain, you need to get the timing set, a timing cover gasket set (that probably will come with the front oil seal but check), and you're going to have to rent a damper/steering wheel puller set. You might as well pick up the timing light as well.
You test the injectors by connecting a DMM between the respective terminals on the fuel injector harness terminal that hides behind the A/C compressor. One set has the pink wire, the other the pink/black wire, and you connect between that and either the green wire or the blue one. Remove an injector connector and find out which set is which (don't have the info right now offhand), and you should read around 4 ohms per bank.

 

i had the same problem, after searching everything a very good local garage found the spark plug gaps to be way out - another garage had just put them in with out gapping them ran fine afterwards !

 

I agree....I just fixed my Camaro.....

Very bad Spark plugs....change them out.....try it....

 

There's only about 1000 mile on my delco plugs, I gapped them myself. HOWEVER, I do think it will run better with some pre gapped ones, like denso iridium of some E3's - I know my gapping wasn't 100% accurate. Has anyone out there had good luck with pre gapped plugs? What about pulse plugs? I put some bosch platinum +3's in it a year ago and it ran like poo. But I honestly think that's just b/c it was the bocsh brand. Ive heard nothing but crap about that brand. My o2 sensor is bocsh, could that be part of them problem? And why would it idle perfectly in park but not in Drive with the brake held down? Wouldn't always run crappy if the plugs were bad? I mean it really does sound like a vacuum leakto me when I say it like this, but I've had them all off twice and they are all new and they fit tight and don't leak.

 

IIRC Bosch supplies O2 sensors to most of the factories out there, so you're not going to get much better than that.

If you have a DMM, I would test my plug wires. No wire should have more than 20,000 ohms resistance (and yes, that's spec).

DON'T get platinum plugs! You're wasting your money! These engines run best on AC/Delco R43TSK plugs (assuming a 3.1). You can re-gap the plugs, but factory spec is .045, if you didn't already know.

Did you check your MAP signal yet, and see that it IS getting a manifold vacuum signal?

 

Mileage doesn't matter these cars tend to eat ign parts like candy at times.

also try running the car in the dark with the hood open, look all over for signs of spark leak.

Then mist the engine with a water bottle and look some more.

In either case any spark leaks is bad.

 

Tell me about it. I hate replacing the ignition module when it overheats and dies in the middle of Main Street in a city .

Also, most ignition problems WILL get worse when the engine is hot because resistances in the system (wires, coil, terminals, etc) go up as the underhood and engine temps go up.

 

I think you are onto something here. I took her out to a late movie tonight, it was in the 60's here and the problem was almost non-existant. I'm going to try and re-do all of the ign parts and see what happens. New plugs, wires, the whole shebang.

 

my car always had a rough idle in "D" too i replace everything on the engine and here's a question what about the IAC i had that go and OMG my car sound like it was CAMMING and have a V8 and the idle was jumping form 400- 950 rpm

 

I had that do bad already, the v6 will just start and then die. I got a knock off one made in mexico instead of the delco one, it works just fine

 

When you replaced the IAC, did you clean out the air passages as well as the back of the throttle plate? Also, does the engine idle nicely at idle when not in gear? It could also be that the smallest of the 3 EGR ports sticks open.

Just a couple of other things to think about after you have checked your ignition parts... It's not hard at all to clean up the digital EGR as it comes in 3 separate pieces, but you have to have special Torx bits to do it.

:edit: Just noticed in your sig that you're running an Accel coil... If you still have it, go back to your stocker for a couple of days and see what happens. The Accel coils don't like being a DD coil as they overheat WAY too easily and short internally compared to our crappy stock ones.

 

mmm

1. intake cleaner
2. or take the intake off and clean everything spotless
3. or so what i did turn the throttle screw 1/4 turn to it's at 700 rpm (stock idle is 675)

 

I've been putting off replacing the egr for some time now. I know napa makes one that is more affordable than the 300 dollar one most places sell. I will go back to my stock ign coil today and let you know how it feels. When I put it back together is there anything I should put on the new gaskets? Like anti-seize or anything?

edit: Yes it idles perfectly in park and neutral, just not in D with the brake pressed down.

 

Can you recommend a good intake cleaner? I've read the tomp (spelling on that?) tune up like a year ago, maybe it's time I revisited it! - Your computer should have re adjusted your idle after 20 minutes of driving

 

Well it didn't adjust lol i must have a slow computer because i did that 2 years a go and i haven't stalled since and been idling at 700. 3M makes a good one or if you want the really good stuff go to a GM dealer and ask for it but its a lot of $$$ they use something that i would compare to brake cleaner in cleaning strength

 

Don't waste your money on a kit from 3M or GM, just get some plain throttle cleaner. It's all the same stuff in a different can. Then run some seafoam through the booster line. I think most of this stuff has been repeated sevral times already, but double check that the map port/vac lines aren't blocked or leaking and skip replacing the whole ign. system, it couldn't have gone bad after only 1k unless you're fouling plugs from being overly rich or burning oil. Once it's cleaned out you can do a min air test with the IAC closed. Should idle at 500 rpm during test, only adjust the throttle stop to set min air.

 

My 1990 3.1L V6 has the same problems but it hunts for a steady idle from 750-1250rpm. What I've replaced...

TPS
IACV
O2 Sensor
Intake Air Temp Sensor
MAP Sensor
Checked Vacuum Lines-All good
Cleaned Throttle body as best as I could
New K&N Air Filter
New Fuel Filter
STP Fuel System cleaner added periodically
All new ignition system
New EGR Valve


I had the computer reset at my local chevy dealer and the computer relearned all of its sensors and got retuned pretty much and still didnt help. My last option is to replace the intake manifold gaskets, b/c when i shoot carb cleaner on them the idle speed changes which is a tell tale sign that they are bad, and these engines are known for bad intake manifold gaskets, and if they havent ever been replaced or serviced it would probably be a good idea to take some carb cleaner and do the same for your V6

Goodluck

 

I would REALLY stress getting it timed. This sounds almost exactly like a timing problem. You may as well go get one at autozone. They are 41.99 and very easy to use. I was able to figure it out in about 5 - 10 mins.

Do a search as to what your timing should be and where to locate the timing tab and such.

 

I always do seafoam through my pcv valve, are you telling me to put it in the brake booster line? Will that work better? - Also, jtnktz - I will try and figure out the timing, it's something I should learn anyway.

 

Well if you were using a metering bottle (what I use at work) you need it connected directly to the plenum for the best vacuum and dispersion. The PCV is normally ahead of the throttle and doesn't have much vacuum at low throttle.

 

When you run the seafoam, do you run the engine at high idle until the smoke clears, or do you shut it off for 5 minutes after it starts smoking and restart it to run the crap out? You're supposed to shut it off, according to the can.

Anyways, A couple of other points:

First off, nobody can tell you much without a scanner and your BLM count, which is the best indicator of what is wrong in there.
Not having one, the next best thing is to get a vacuum reading, both in Park and in Drive (with the wheels blocked and chocked and the parking brake set, of course).
I also recommend a timing check. Best get a timing light... if you keep this car, you're going to be using it A LOT.
A fuel pressure reading would also help a lot. Test not only with the engine running, but after you shut it off as well. The fuel system should hold pressure for 20 minutes after you shut it off.
Did you resistance test your plug wires and injectors?

Another thing to try is a fuel injection cleaning. If you get the can stuff, just hook it to the pressure port. I've found that the "in tank" fuel injector cleaners don't really do much of anything except waste money, and I've run pretty much all of them. You can have a shop do this, but expect to pay a lot for it... A local dealer here charges $69.95 for a Fuel Injection Service, and when I had one done at Pep Boys a few years ago, I had to shell out $240 (for nothing, nonetheless... The engine still ran like crap). I don't remember who makes the stuff in the can, but it is like the newer A/C recharge kits in that it comes with the hose attached to the can, which you hook to the pressure port, disable your fuel supply (both the relay AND the oil pressure switch need to be disconnected), and pinch off the fuel return hose so the cleaner doesn't end up in the gas tank instead of flowing through the injectors.

 

I got it running a lot better, but there's still a hint of the problem. I threw away the accel coil like you guys said and it almost 100% eliminated the problem. Instead of the engine jerking around constantly while in drive with the brake depressed, it just gives a slight almost unnoticeable jerk about every 3 seconds. There is a slight poot of air that comes out of the tail pipe when this happens. What is that?

 

Glad to hear things are finally improving. Now that you're heading in the right direction:

One cylinder seems to be missing... We need to find out why now.
1. Beg, borrow, or steal a compression gauge and get some readings.
2. Same with a fuel pressure gauge.
3. Resistance test (ohm out) your injectors and wires.
4. Check for a bad or fouled plug. Don't just look at the working end of the plug, look at the whole thing. Check for cracks in ceramic insulators or other evidence of misfiring. Also check to see your plugs are completely seating in their bores by cleaning the threads in the heads and look at each plug as best you can with the engine running. Any mixture that is escaping the cylinder around the plug will look like a sort of fog around the plug.

 

so the parts I need are a compression gauge, a fuel pressure gauge, and a resistance tester? Ok, I'll try and collect that stuff at autozone, they are usually pretty helpful. Just curious why missing on a cylinder isn't felt during driving and also why I don't have any codes stored? Additionally, when I'm running the seafoam through my system, I get a little of the smoke comeing up from the back of the engine but I can't tell from where, the nipple on the back of the upper intake plenum isn't leaking so I must have a cat/exhaust gasket leak right?

 

Hey... I just realized that it was you who has been PMing me. I have read this post and now have more information...

DO go get yourself a vacuum gauge and hook it up to see what kind of vacuum you are pulling when it is idling. My car got to idling terribly and missing badly when idling. It seemed to run fine when I was going down the road. When I hooked up the vaccuum gauge, I found out really quickly that I had a vacuum leak. I was only running about 5 or 6 inches of vacuum, instead of the 17 or 18 that I should have been running.

One place that most people overlook when checking for vacuum leaks is the valve covers. There is a tube that runs from the passenger's side valve cover up to the air intake tract right in front of the throttle body. Pull that thing off and see if you are getting any air pulled in through there. Most people don't think about that one, and since it is pulling air through the air intake tubes, YOU CAN'T HEAR IT!

If you have a leak there it can only be one of two things... Either your PCV valve is bad and you are pulling air through there, or you have a bad gasket somewhere in your lower intake and the vacuum leak is inside of your engine and pulling air in through that tube. It happened to me! I am going to have to take my own intake off and replace a leaking gasket somewhere. Once that is done, it should be back to normal.

Exhaust leaks upstream of the catalytic converter will kill your efficiency since your 02 sensor will be giving bad readings. Fix ANY leaks between your engine and your Catalytic converter. The 02 sensors in these cars are not heated and need to be at about 650 degrees to give a good reading. If you have an exhaust leak, your exhaust temperature at the 02 sensor will be too cold, and also you will be getting extra air (oxygen) into the system. Either condition will cause the 02 sensor to send a signal telling the computer that the car is running lean. The computer will then add more fuel to try to correct it.

 

Those were 2 leaks I had a heck of a time finding... The intake bellows was torn at the end of the metal tube running to the pass side valve cover, and the nipple the tube fits into wasn't sealing into the head properly because it was worn out. The other was the PCV valve, the nipple that fits onto the end of the valve at the plastic tube that runs down to the nipple down by the base of the dizzy, and the nipple on that end of said PCV tube, which I sealed with black electrical tape (not the recommended way to do it, but it IS really difficult to find some of these little parts, and hey, it works).

Let me just say this: my 2.8 was swapped out by a friend of the family who owns a shop back in 2004. After the swap, the engine ran like GARBAGE, really bad, even worse than yours, and the only code the 3.1 threw was a 32, for a badly connected and not working EGR system (had to replace the solenoid AFTER I properly hooked it up to the TB). I got roughly 25-27 MPG on the highway, with my auto trans, when the lockup actually worked. I replaced the plugs, the cap and rotor, and finally the fuel injectors (2 ohmed out to be REALLY bad), and after I finally replaced the last 2 injectors that were on the engine from the junkyard, I noticed a LARGE change in the engine exhaust note from my Flowmaster and drivability... I now get 30+ MPG on the highway.
The whole point of that story is that things can be absolutely wrong with the driveability of your engine, but the ECM will not throw a code unless something is WAY out of wack. Now, if I could just figure out my code 45, I'll be set.

:edit: And that's a funny thing with something being slightly out of place. Our engines turn about 600-700 RPM at idle when hot, and about 2000 going down the road. The difference between being stopped and idling and going down the road covers up the problem because there is less time between cylinder firings for a misfire to be detected by the butt dyno. Which is why OBDII has a misfire monitor. However, once you REALLY get to know your car and your engine when it is running right, you can hear and/or feel when something just isn't right.

 

Actually, the reason you couldn't tell when you are going down the road is because the computer will compensate for the vacuum leak at that RPM and load. The 02 sensor will pick up that the car was a bit lean, and then will add some time to the injector pulse to compensate.

My car ran fine when it was going down the road, and I didn't notice any loss of power or efficiency... It just would idle like CRAP! It also would die most of the time when you tried to slow down to turn in somewhere.

Usually, if my car has a miss at highway speeds, I can feel it. When going up a hill and in overdrive with the converter locked up, it would shudder every once in a while. I would then change plugs, cap and rotor, or whatever to get the miss gone.

Right now, I am still driving the car, but will be pulling the intake back off very soon to set things right.

I hope that you find what is wrong with your car Ohiotemplar. Vacuum check and a cylinder compression check will go a long way towards determining your problem.

 

How does a timing gun tell you if your chain has slop in it?

My 89 TBI has a slight stumble at idle. I can see the RPM's dip so slightly sometimes when it does it. The other day when I was at the back of the car, I could hear the stumble sound coming from the exhaust as well.

There is a noise coming from the engine. It sounds like you have a bag of coins, and you barely shake it every so often. That is what it sounds like. A shop in the past said it was from the tensioner pulley. I took my stethoscope, and it sounds like it may be coming from the timing chain cover, which would be the timing chain. But I'm not sure. I've replaced everything else that can think of.

 

take your cap off and look at your distributor, if you can take it off and see if it rotates without resistance, but if it looks rusty it might be a sign of something bad....was on my car

 

I am sick of my similar problems with my 88 firebird 2.8 MPFI. Except mine won't start sometimes until the next day.

I have been reading and researching for hours now. I am broke and I am not going to spend hundreds trying to figure out my problem.

The V6 and computer crap is coming out!!

350 V8 carburetor swap is the future of this car, and my 91 Firebird also!!

I just kinda sucks that I am not working right now since I lost my job 3 weeks ago, am broke, and these junk Firebirds are my only transportation.

No transportation = No job.

No job = No carbed 350 V8 engines.

No carbed 350 V8 engines = No transportation.

Vicious circle.


I am DONE with computer controlled 1988 and 1991 Firebirds.

 

Wow....LOL....


I feel the same way when I thought my car and I were the only ones going through this lol....




Hang in there man and hope you get it working lol...

 

I think they all have some sort of hidden internal clock to become a PITA after 20+ years.

Im done going to carb, F the computer stuff.

 

Not trying to be rude, but it's easy to blame things you don't understand. I'm often frustrated by the complexity of efi, but once I find the problem I think back on how simple the problem actually was and how easy it would have been to correct if I hadn't jumped to conclusions. You have to follow a thought process to identify the problem. Look at the symptoms as a whole first. What system or sensors are responsible for controlling that malfunction? Test each individually until you've exhausted all possibilities or found the problem. And if you're frustrated stop and look at it later.

 

you can feel free to come over and work yourself in a tizzy trying to figure mine out anytime. As I stall for any reason not to slap the carb off the s15 I just bought.

 

Few hundred miles farther than I'd like to drive, LOL. Would like to get a look at that hatch you have.