FYI - 1986 Firebird 2.8 V6

I'm going to describe this in detail, and see if you guys have anything.

So far I have replaced---

-Throttle Position Sensor
-Idle Air Control - twice
-EGR Solenoid
-Almost all vacuum lines, the others seemed fine
-Entire throttle body - a shop said it was because it needed a new return spring. Didn't change a thing.

All of these things I replaced on my own, but the only thing I've gained from them is knowledge, because I've still got a problem.
Ok, here come the details:

The problem is - sometimes I idle at anywhere from 2,000-3,000 RPMs.

When it occurs - USUALLY the car will drive fine for a full session (start to stop) but then once I get in the car again and the engine is still hot and start it up, the idle flys to 2500 immediatly and stays there. Sometimes this will go days without occuring. Sometimes it does it all day. RARELY it happens while I'm allready driving and everything is fine. Start up really determines how my trip is going to go.

This is such a strong problem that I cannot go into 4th gear if I want to stay around 30 because the idle will pull the engine up to 2,200 ish. I've got to ride the brake when this happens.
When the car is normally running, the power is awesome for it to be a 21 year old V6. It drives perfectly when the idle is fine.

-EDIT ----- I should also mention, about once every 2 weeks, it won't start unless I give it some gas while trying. And once it is, it seems to want to stall out for about 5 seconds and then it will run fine. Don't know if maybe this is attributed to the same problem.-----


Other suspects:

-The actual EGR valve. Can someone explain how to test it. I guess I'm bad with the search, I know its on here but I can't find it. I'm thinking maybe its just rusty/dirty and sometimes won't move to control the vacuum. But since the problems happens so exactly sometimes (on start-up) that makes me doubt this.

-Bad ECM - Maybe when it starts sometimes it just misses something. But the fact that it runs fine until started while its warm also makes me doubt this.

-The TPS isn't dialed in - The fact that it can run perfectly fine also makes me wonder if this could even be it.

I really can't think of anything else. I'm only 17, had the car for about a year and a half now, so I'm still learning, but I'd love some opinion.

 

idk man.... To me it really sounds like the IAC is getting stuck when hot. Maybe the stepper motor driver in the ecm is getting weak, but that is just speculation.

 

Do you know of a way I can test the IAC?

 

IIRC the 2.8 had a specific idle learn procedure that was different than most which sets minimum air then teaches the ECM the IAC position. I don't remember what it is but I have a Mitchell manual that gives step by step.

 

did you replace the throttle body with a used one? If so maybe you gota give the entire thing a good cleaning inside and out. It might be covered in carbon which may be causing the idle problems. Also, may I ask how you painted your intake like that? I'm thinking of doing that but in black. Looks awesome!

 

this seems to be a common problem with GM EFI. my sisters 3100 cavaler did the same thing, my dad replaced a bunch of parts without ever figuring it out. my brothers girlfriends 3100 pontiac grand am did the same thing with the same result, replaced a bunch of stuff without ever figuring it out. both cars were sold with the problem. (disclosed to the new buyers of course)

MY gta is/was doing a similar thing. idle would stick as high as 2500. i could get out and open the hood and the throttle blades would be phisically stuck open. i cleaned the **** out of the TB and it got a little better, the thing that mostly fixed it was installing a big *** external throttle return spring. it still idles at 1500 sometimes, usualy on warm start up. i switched IAC with my 2.8 car (same IAC) and it did not help at all. i checked the TPS, all good. at this point i have attributed it to the TPI/EFI "false high idle" GM built into the ECU so people used to carbs would not freak out. it usualy only happens for a few minutes, it just makes the car sound like apiece of ****. one day i'll convert to a holley commander or megasquirt and it will go away. (or LSx ECU )

 

has anyone tried to see if the problem only exists in open or closed loop?

 

Actually it's the 3.1 that has the Idle learn procedure... The 2.8 is just plug and go.

 

I beg to differ on this one. After I unhook the battery and hook it back up my car runs like crap for a day or two.

 

About the throttle body...I cleaned it up a ton before putting it on there.

I should also mention this, the problem was very minor when it started, the throttle plate was just sticking and so we cleaned it out with some throttle body cleaner ::NOT carb-cleaner:: and after that the problem multiplied to what it is now. So somehow cleaning the throttle body/plenum and loosening up that stuff in there ruined my idle.

My dad thinks its the ECM gone bad. He bought a new one today so we'll see.
He also has a theory that I think is somewhat crazy about the catalytic converter being clogged. He thinks the exhaust is getting stuck in the manifolds/y-pipe and making the car idle high....I think this would just kill performance and make the car stumble...but who knows. He wants to take it off and gut it. I'm ok with that anyway. Here in FL - no smog tests. Just visual, if they feel like getting on their knees.


My best guess from here is the EGR. If I push up on the valve while the car is idling high, it will drop dramatically. But once I let go, the diaphram drops back down and the idle skyrockets. Also, when I diconnect the hose to it, I can't feel any suction. But when I disconnect the fat hose that connects to the hose that connects to the IAC opening part (confusing?) There is a TON of suction. Disconnecting that actually makes the idle drop from 2500 to 1500 then it slowly creeps back up again.

I think I should replace the EGR valve. I posted another thread about replacing it if someone could help me out with that one.

Thanks for the replies guys.

Oh, and for 1989karr -

Thanks for the compliment. I was really happy about how the paint came out, too. I got some Ford Red engine enamel from AdvanceAutoParts, its rated up to 500*F. Basically I just got some masking tape, taped off the rest of what wasn't going to be red (took a while) Layed some newspaper down to take care off the windshield and what not, and sprayed it on. I'd clean it beforehand if you do it my way, I had some trouble with the tape sticking in certain areas.
I had some places where the paint seeped through, so I got some Q-tips, dipped the end it acetone/paint-thinner, either one, and rubbed off those spots. Worked well. At first it just smears, but after some more wiping it dissapears.

 

After reading your posts..now this is my opinion and you can do what you want with it.Some of the things you discribed tends to lean me towards worn throttle bushings...once you cleaned the throttle body out, it removed some of the soot sealing the excessive clearance in the shaft..allowing more air in to enter..thus causes problems with the ECM/IAC cause it has too much air ..ECM cannot control the idle...Take the throttle body off ,take it to a machine shop and have them inspect it ,put a new gasket on..Sometimes you can feel the play in the shaft if you physically move the plates up and down..a stuck throttle plate is usually a sign of worn bushings.Might want to check that out.

 

thanks! I'm definetley going to try that. Oh and as far as the idle, this just came to mind. When you put in a new IAC, did you adjust it properly? I'm not sure about the IAC in our F-cars, but for the FWD 2.8s, you have to adjust the IAC before installing it or else you'll have a ton of idling problems...trust me, I know about that one lol

 

Throttle bushings...this is new to me...can you explain in more detail? So there is actually a seal that sorrounds where the throttle plate touches the metal when closed all the way? Sounds like a big possibility. We scrubbed that thing down. Both of them.

The IAC - all the paper that came with it said was to mae sure the needle was less than an inch or so (I think) out, or else it would be too far out when putting it in. But it allready was that short in the box, so I didn't need to change it.

My dad read some more websites about it and found out some new stuff.
One site said that the injectors may have gone bad. I'm sure the original ones are in there.
And another said it could be the MAF and to test that, to unplug it while it was idling high and see if it idled down. Sounds good to me, but new ones are expensive so I'm hoping if thats the problem, the JY will have some working used ones.
After having my car for just a little over a year, I'm starting to learn that:
car = way more money then I ever planned on spending on it.
Oh well, I love the car. And one day, I know the car will love me back

 

Throttle bushings arent a seal more like a hollow metal shaft that surrounds the throttle plate shaft in the body.If the bushings wear..it allows additional air thus ,making the computer hard to control the amount of air entering the engine by the IAC valve...Usually its worn due to high mileaged vehicles.Again most machine shops due this sort of repair..theres a number of things ,so without actually viewing your car,this is just a suggestion..from your symptoms.

 

Allright. Well I guess the only way for me to really investigate that one further is to take it back to a shop and let them tell me if the bushings are still intact. I don't think I understand enough to know what I'm looking for. The bushings sorround the plate?

Thanks for all the info so far guys.

 

No, the bushings are around the shaft that the throttle plate attaches too.
You have to remove the throttle plate and slide the shaft out and you will see whats left of the bushing or no bushing and possibly the throttle body is worn out.I never attempted this task ,but was told machine shops do this rebuild.You would have to consult them...

 

1. That big black hose that runs from the back of the intake to the TB IS the idle air inlet for the ENTIRE engine. Without that hose, you're stuck with the bypass air running around the throttle plate, and you have NO IAC control. How do I know? I broke mine three years ago, before the 2.8 died, and the guy who put the 3.1 in did NOT swap this piece over. I ran WITHOUT one for almost two years until I replaced it with a rubber hose/PVC elbow assembly.
2. Check said pipe for breaks, especially at the T where the big parts come together, and the elbow that runs to the PCV valve in the driver's side valve cover.
Check the top portion of the TB for broken gaskets. You can get a gasket set at parts stores, or just use silicone gasket maker. Also check for valve cover leaks, misadjusted TPS (.55VDC between the middle and lower terminals), unscrew the idle stop screw as far as it goes and then try setting it again, test between the 1st and 3rd and 2nd and 4th terms on the front 4-pin connector of the injector harness for 4 ohm resistance per bank.
DON'T bother with a USED MAF!! You are NOT going to find a GOOD one! Go to partsdirect.com, and spend the $80 for a NEW one!
If you are still looking for another TB, you can have mine from the 2.8 top end. It has a NEW IAC, cleaned passages, and a newer TPS. But it's not free.
The guys with the 88-89+ engines don't have the same intake system that the early MFI 2.8's had, so take their advice carefully. All of their intake air goes through a passage in the newer style TB, right into the front of the plenum, where as us older guys have that damn (no part number and good luck finding a good one in a J/Y) black nylon tube running off of the intake nipple to the nip on the TB, also to the vac source for the EEC can, and the PCV valve. Check your emissions sticker and check the entire black hose assembly for melting, cracks, etc.
Also check the brake booster hose and check valve, the vacuum tank ball on the driver's side, the cruise transducer, etc, by disconnecting them and running the engine. Either way, the engine is getting more air then it should. Also, have you tried resetting the ECM?

 

Thanks for the offer, but I actually had just put a new throttlebody on when I started the thread. The gaskets are good, since we put new ones on when replacing the TB.
And we just put in a new ECM, and I mean new, so that should be set.

My dad cleaned the MAF this morning with some MAF cleaner, and I had no problems today. So, we'll see if it keeps it up.

 

Update - Nope, the MAF sensor cleaner didn't fix it. It does seem to be running slightly better, but the idle problem persists.

EDIT - My dad has been emailing someone online who says the problem might be the cold start valve. He says it might just be sticking open sometimes and putting more fuel than needed into the engine and the ECM doesn't read that. Who knows? We'll try it anyway.

 

what are you going to do about the cold start valve? I've been looking for a new one but its been discontinued and nobody seems to make it!

 

Excess fuel will only bog the engine, not make it idle high. (unless it's a diesel LOL)

Have you checked the fuel pressure? replaced the fuel filter?
It's not always the case, but lack of fuel can at times cause similar symptoms to what you are describing here.

Also have you checked for gasket leaks? Take some WD-40 and spray it along all the seperations between the UIM, MIM and LIM, if you get a point where the idle drops, you've found your leak. The only problem is this only eliminates external gasket leaks, since you can't really space it between the LIM and head.

The reason opening the EGR valve, causes the idle to drop, is because of the lack of good unburned oxygen in the exhaust gases, being re-introduced into the intake tract.

If you haven't already gutted your cat, get a pressure gauge, one that will read low pressure (0-15 PSI or so), make an adaptor for your O2 sensor bung, to the gauge. Start the car (don't worry you won't be running it long enough to really worry about the lack of O2 feed back), and make sure that the pressure doesn't go above 2 PSIG or so. If it does, you have a restriction in your exhaust, possibly the cat.
If you're really worried about not having the O2 or you want to do some farther testing, like while driving and such, add a bung to your exhaust, and run this seperatly. You will also want at least 2 or 3 feet of hard tube (metal) between the bung and any soft (rubber) hose to run to the gauge, to reduce the heat in the line, and keep the line from melting.

Go over all the electrical, make sure that the sensors are receiving and sending the proper signals. When I did the engine swap on my truck many years ago, I somehow missed the ground for the TPS, and because of this the ECM thought the throttle was at WOT, and would not enable the injectors (Clear flood mode), found this, unplugged the TPS and BAM, fired right up.

 

Have you checked all the connections to the Throttle body, IAC and MAF. I had a similar problem with my 3.1 but after cleaning the conections and making all the conectors tighter it has fixed the problems.

 

About the cold start valve - I actually haven't started looking for a new one, so if they have been discontinued like you say, I'd probably just try to find a good looking one from a junk yard.

Cleaning all the connections sounds like a good idea, what would you recommend cleaning them with that won't harm them?

Gasket leaks- if there is one, it would be between the LIM and the head, because the rest have been replaced and I've sprayed carb cleaner all over this thing, didn't get any drops.

The coolant temp sensor has been something I've been wondering about. If it is reading wrong, I've heard this can cause idle problems, and since they always seem to be happening when the engine is at running temp, it seems like some problem might be comming from this.

My cat is pretty well gutted. When we got the car we could hear some broken up charcoal stuff in there making noise, so we sucked all that out and got alot out.

I actually can't get my 02 sensor out. It's so stuck in there, I'm 99% sure its the original one. I should mention this, too - I have a air/fuel ratio gauge hooked up, and alot of times I can be on the gas and the gauge will read somewhat lean to ideal, but when I let off the gas anytime, it jumps to really rich just for a second and jumps back to lean. Even if I tap it it will jump to rich for a second. Sometimes this doesn't happen, but alot of the time it does. Possible sign of a problem there?

The exhaust shop wants $100 to weld in a new bung. I think thats crap, especially since I myself know how to weld, I just don't have a welder .

Question - When the EGR's diaphgram is UP, then it is closed, right? Because sometimes my car will be at operating temp and the diaphgram is still down and when I push it up, the idle drops. But I always thought when its UP it is closed. Am I wrong on this one?

I never thought a lack of fuel would cause the high idle. How would I check fuel pressure? Someone told me the injectors could be bad and causing the high idle.

Keep in mind this is the first car for me. I've learned alot, but it's still comming...


There are so many possible things that could cause this, but the part that keeps playing in my head is that it only happens sometimes. After the car has been goin for a while, or right on start up while it's still very warm. Something is happening when the car is warm that is causing this. I've NEVER had the car idle high when starting it in the morning.

Once again, thanks for all the help and ideas.

 

EGR up = open.

The EGR will open and close in relation to throttle position, and otherparameters, controlled by the ECM. Usually you will find that as you rev off idle, the EGR will pull up a bit, and if you were to go farther the EGR would start closing due to lower vacuum.

Cleaning connections can be done using carb cleaner or electrical contact cleaner.

There should be a test port on the fuel rail, where you would connect a fuel pressure test gauge to check the fuel pressure, refer to a service manual for proper procedure and spec.

 

I'm confused then as to why opening the egr, or pushing the diaphgram up myself, would lower the idle. It lets the exhaust into the intake again? If that's it, then I understand.

Allright, well I guess that means me EGR is all good then.

Anything you know about the coolant temp sensor?

Thats one thing next on my agenda.
My AC doesn't work, so I don't use it. And I never use my vent option, I just put the windows down. Here in FL it works better, I think. Anyway, one time my dad moved the AC/vent/heat **** just to see what happened and the idle shot up and couldnt decide where it wanted to stop between 1500 and 2500 RPM. I don't know why I haven't checked this out yet, I guess because I never use them, but do you think this could cause a problem somehow even without moving the *****? The AC controls use vacuum don't they? Or are they electrical? My dad thinks vacuum.

 

Did he turn the AC off? When my AC is on my RPMs drop alot at idle.

 

yeah, usually thats what it should do because it pulls on the engine.

But when he turned mine on, the idle shot up to 1500 - 2500ish.

 

So far, it actually seems like the MAF sensor cleaner helped alot. At first it did have a few bad times, but in the past 2 days its been much much better about the idle. It still doesnt just drop right to 800 like it used to, but it does get down there after a few seconds.

I'll still clean connectors and whatnot to try to get it even more precise.

 

yes there is vacuum, actually 2 one for ur vents and one for ur heater valve that runs back into the engine bay i would check those out maybe it's just a little pin hole i got mine disconnected and capped for the timje being so i can totally rule all that out till i get MY idle/red cat problem figured out.

good luck dude

 

Take the MAF out and look at the orange film inside. If it's not completely flat, the MAF is BAD. Go and get a NEW one for $80 (with a lifetime warranty). Also swap the relay next to it (the MAF relay, BTW) for the one for the fuel pump.
Also, check the adjustment of the idle speed screw on the TB. Sounds like it's too high. The screw is at the cable side, up at the top of the throttle arm thing, and might be plugged by a welch plug, which you just knock out with a punch. Adjust this screw with the engine running, in Drive (Autos, with the parking brake set and the rear wheels either raised or blocked so that you don't get run over), and adjust until you get around 700 RPM (Auto, Manuals around 600 RPM). I myself prefer 900 RPM idle speed so that I don't have to adjust it higher in the winter, and it starts easier from a stop.

 

actually i would try that maf and keep searching for a vacuum leak b4 adjusting the screw cause if the cap is still on it's set the same from factory and does not require any tuning afterwards unless u really know what ur doing cause u can really mess things up with that screw.

 

Actually I've allready messed with the idle stop screw, on my old TB and on the new one. You actually get a code when it is set too low, so I set it as low as I can without getting a code and its been at a good steady 800. Before all the problems my engine never went below that either, so I'm good with 800.

I still haven't had any problems. But I've been gone for a week. Today went good though. Thanks for all the continued help.

 

800 is a good idle. For some reason mine won't idle below 1000, I almost have the TB closed and it still won't go lower than that, but it's noce and smooth so no complaints.

 

Just an update.

I'm only getting a problem once every 2 days or so. I like it.

I'm beginning to think that cleaning the MAF did the trick, but it still just misses every once in a while and the voltage somehow gets thrown off when I start the car. Alot of times comming to a red light, stopping the car, flipping the ignition back and forth and starting it again will clear the problem (atleast for a few minutes )