My ride is an 1988 GT.

Once the engine warms up, waiting at a red light, it will idle around 800-900 rpm then suddenly hiccup, drop rpms and surge back once or twice and stall out. If I pur my foor on the gas pedal and hold it at 900-1,000 rpm it will continue to run ok. The engine has wear (175,000km/120,000mi). I've had the car for just over a year and have sunk a lot of money into restoring it with the goal of making it a personal distinctive driver. The 125 tranny has been checked twice (once to install a new lock-up solenoid) and both shops tell me that there's still lotsa miles before I need any work done on it. I have had the engine serviced and a tune-up including new distributor cap, wires and plugs. Following factory and after-market service manuals I have replaced the TPS, the IAC 3 times, the best being a used original equipment one. I have cleaned the throttle body and the IAC seat and vent hole. There is a new Oxy sensor and I have tried a new after-market MAP, returning to the original after noting no change. I am using an oil additive that keeps the oil pressure very high when cold and above the redline when hot (as I thought possibly a low oil pressure would somehow affect the idle problem. The car has the cat removed and I installed a resonator in it's place to keep the noise in the range I like. Therefore the MAP is disconnected. (This was the way it was when I bought the car, and yes, it had the idle stall problem at that time). I have installed a complete new set of injectors that has marginally inproved the overall engine performance. BTW the car will stall in netural as well, at the stoplight is I just let it idle without putting any pressure on the gas pedal. From different forums I have done a number of other things, like adding a new ground aa well as my share of hair-pulling and nail-biteing when the idle problem continues.

Supposedly a fellow in WA was going to supply and install a rebuilt DOC and 4 speed A/T last fall, however I ended up getting ripped off for the $3,000 instead. (Needless to say, that is a matter which still has an unwritten chapter). My Plan "B" is to get the 2.8 rebuilt locally either as stock or with a stroker and cam package. Before doing anything more however, since I don't have an unlimited cache of cash, is to get the engine idling properly, BEFORE I get it rebuilt so that I will have some confidence in ending up with a smooth running ride.

I know this is long, and there's probably a number of things that still I have missed mentioning. My Fiero is in much better shape than a year ago and (mostly) it has been a great experience. Any suggestions on my idle problem would be most welcomed.

Thank U

Ron

After thinking about all your wrote I wondered about the fuel pump.
When you turn the key on does the pump do the 2 second run before you start the engine?
Do you have to crank the engine for several seconds before it starts?

The idea is that if your running off the oil pressure switch and your pressure gets low at idle (since you seem to indicate you have a oil press. problem) the fuel pump shuts down. Keeping the idle higher keeps the pressure up just enough to prevent the problem.


You could try jumping the fuel pump on the ALDL connector and see if the problem still occurs.

If that's your problem you need to check your FP relay and figure out if it's the relay, wiring, or ecm control to the relay.

[This message has been edited by Dodgerunner (edited 12-29-2006).]

you said in your post you removed the cat, put a resonator in it's place, therefore the MAP is disconnected??????
the map needs to be there. so does the O2 sensor. the cat has noting to do any sensor, it is an after the fact thing.
verify that the MAP sensor vacuum lines are intact, they run under the plenum, so they can be hard to check. a Vacuum guage on the MAP connection would be a good idea, verify that there is vacuum there. it is on a T fittin, make sure the other end is also connected properly.

I have EXACTLY the same problem on my 86GT and have replaced virtually every sensor, added grounds etc, with no change. What Dodgerunner said about the fuel pump and oil pressure kinda pops out at me. My car starts instantly, has good power, the engine timing is spot on, and the gas mileage is ok for 128k miles on the clock, but the stalling is making me nuts. If you fix your problem be sure to let me know what you do, and I'll do the same

TJM4FUN: Thanks for the input. The EGR has been disconnected and the vacuum line capped, not the MAP...sorry for the misinformation.

DODGERUNNER: TY for the suggestion. I have NOT checked the fuel pump relay. I AM getting 2-3 seconds of the pump running when I turn the key on. The ALDL test on connector "G" would just run the pump I assume...which I'm currently getting on turning the ignition to "on". I also haven't checked fuel pressure from the pump, since it seems sufficient at normal driving speeds and "flooring" the gas pedal when driving. accelerating without any stumble.

Here's an response by JAZZMAN posted to a not directly related question, that if I apply it to my high mileage engine, got me thinking that possibly the engine itself is the culprit - but that's just a guess on my part, and I really would appreciate comments. Jazzman wrote something like this...."An engine running on only some cylinders won't keep running, reason is unburned oxygen coming out of the dead cylinders fools the ECM into thinking mixture is too lean so it starts adding fuel to compensate. At some point it will get so rich that it won't run or barely run at all." Could this happen in this manner when idling a very loose engine, even tho it is firing on all 6 cylinders?

Is it possible that low cylinder pressure at idle on one or two cylinders could cause the ECM to initiate incorrect fuel mixture and basically choke it? Occasionally at hot idle it will catch itself and increase rpms...then hunt a bit until it stalls.

Dang! I just love writing about something I apparently know too little about.

Ron

What Jazzman says could be true, would think the cyl would have to not be getting any gas also.
If it was that bad you would have a very ruff running engine which I did not see you say. Is it running ruff or fairly smooth off idle.

Have you run a compression check?

Do you have access to winaldl. Would be interesting to see some logs to see what the IAC and other sensors are reading.

Would also be interesting to put a volt meter on your cig. lighter and see what the voltage is doing when you try to idle. A voltage prolblem could also cause it to die and the ecm has a routine that ups the idle if the voltage drops to low. Could be what causes the couple of jumps before it dies at it tries to recover.

NP, you just had me a little cornfusicaled.
Some easy checks:
Votlage as per Dodgerunner's suggestion.
A vacuum guage on the motor when failing, watch the needle, look for fluctuations in vacuum. would be good to do it while warming up thru to the failure point to get an idea if there is any change there.
Since it does it at idle, and when warm, I am guessing you can make it do it sitting in your driveway.
let it go to the failing point. if it stalls, pop out a couple of plugs real fast and look at them. see if they are wet, or black or even very white, they may point at something. (I hope you aoready repalced the plugs, cap and wires....)
try running the ecm in test mode, see if it fails then. to do that, short the aldl a/b while the motor is running, and watch the check engine lite. it will flash on/off in closed loop with the cycling of the o2 sensor going rich/lean. if it isn;t flashing, something is amiss with the fuel mix ot the o2 sensor got whacked from the fuel additive...
doing a winaldl log of the failure is a good thing too, but not everyone has a laptop or the ability to build a cable, so you have look at the easy basic checks first...

You can get an accurate volt test at the cig lighter? That makes that check a whole lot easier.

Makes the check easy and it might better reflect what the ecm is seeing for voltage not what is at the battery. Could indicate if there is a problem with voltage loss from bad wiring.
If it's low at the cig lighter then check at the battery to see what the difference is.
The ecm does receive it's power thru different wiring than the cig lighter but still a possible good test.

[This message has been edited by Dodgerunner (edited 12-30-2006).]

I hate to see this thread die with no progress made, so bump

I would check if the set screw for the throttle plate has been messed with. Maybe the previous owner tried to adjust it.

maybe an IAC circuit problem? make sure your mechanic isnt just throwing parts at the thing and is actually testing the circuit.

PROBLEM SOLVED !!

The distributor was responsible for the stalling. (I had previously replaced the module, rotor, cap, wires, plugs and coil with no real improvement). With the new distributor I now have a steady 700-800 rpm in closed loop warm idle, much improved smoother overall performance and some peace-of-mind after two years of head scratching. It's still a 120,000 mile 2,8 with an exhaust leak that needs to be dealt with, but u wouldn't know that seeing the smile on my face as I boogie down the road.

Hope this helps someone else.