When I bought my 88GT off the back lot of a local used car dealer, it had the cat replaced with a straight pipe and the vacuum line to the EGR plugged off. Apparently the dealer had invested in a rebuilt ECM + chip in order to get it running, since it came to them as a non-running trade. (It was running in a rough way when I bought it.) I don't have to worry about testing here, but I am wondering what the ECM commands to the EGR are doing, if anything....and would I be better off finding someone to burn a chip with those commands deleted? From reading the Fiero Service Manual it appears that there is no signal at idle, from which I assume would have no bearing on my now moderate idle stumble. In closed loop it will be steady at 800 rpm at a red light for about 15 sec., then choke, drop 100-150 rpm, then recover to 800-900 rpm..idle at 800 and repeat. I've replaced both the IAC and TPS with both good used and aftermarket product, neither methods making much difference in the stumble.

I realize I started asking about the EGR and wandered.....I'm sort of following some business advice received years ago....."When in doubt....mumble".

Solving the idle stumble seems to have been my basic goal for the last couple of years....If I ever get it solved, I wonder what will be next to keep me awake nights?

A swap of used distributors recently reduced that stumble considerably. I also swapped used coils and had the cap, wires, plugs and timing done by a licenced mechanic. O2 sensor replaced, Could engine condition (120,000 miles) be the root cause? It's the stock 2.8 with no history known. No smoke, no major oil comsumpion....Lousy gas mileage, but that could be my heavy foot and driving in city mostly.

If anyone has a clue about what I'm talking about..please let me know...

to see if the egr is the cuase, simply unplug the vacuum line going to the egr, and plug the end of it with a golf tee, then drive it around to see if the problem is still there

The EGR even disconnected could be leaking. You can remove it and check the valve on it. They get carboned up and don't seal properly.
Idle issues can also be caused by the MAP sensor. If you buy a new one from GM you will get the newer updated MAP sensor. The original Fiero one is obsolete.
Lastly, Check for vacuum leaks. The EGR tubes can crack and the hard plastic lines that run under the plenum can split from heat and cause leaks.

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quote Originally posted by Oreif: The EGR even disconnected could be leaking. You can remove it and check the valve on it. They get carboned up and don't seal properly. Idle issues can also be caused by the MAP sensor. If you buy a new one from GM you will get the newer updated MAP sensor. The original Fiero one is obsolete. Lastly, Check for vacuum leaks. The EGR tubes can crack and the hard plastic lines that run under the plenum can split from heat and cause leaks.

i highly doubt a vacuum leak is causing his engine to stall out at a traffic light...sounds to me liek a faulty EGR, or a sensor problem..

use carb cleaner to test for vacuum leaks first, spray the entire manifold area, the throttle body gasket, vacuum lines, anywhere there could be leaks. if the engine idle drops when you spray something, then youhave a vacuum leak

This should get you going:
http://spad.sytes.net/fiero/egr.php

10 years ago the auto part stores had a plate to go over the egr valve you could check to see if this is still available...it would clean up the engine bay..people use to make a cover out of roofing sheet metal or some such thing..How bad is the gas MPG?? what code do you get?? the 2.8 seems to have a good record,if you have had the car for a long period of time you should know just by the running of the car day to day how tight the engine is.In the morning at first start check the rear end to see if there is a puff of smoke,or if you sit with the engine at idle for 2 minutes,when you accelerate is there a puff of smoke this is a sign of harden valve seals,not a big deal, a large puff,not so good If you can idle at a long stop light and when you accelerate from the stop and there is little or no smoke this is an indication of a good engine,for a 120,000 mile engine,if the idle is fairly steady when it is at 800rpm before the drop this is an indication of a good engine.. CODES?? a bad coolant temp sensor will cause poor gas milage and bad idle ,,it is the most common problem for the idle and poor gas mpg together this part is difficult for the average car owner to check,you seem to have extra parts so replace this..on most cars you ground the cts with the key on and the gauge will go full scale or the light will come on .. the proper check is to put it in hot water with a thermometer and check readings at different temperatures,,some one advise if simple cts ground check works on fiero.. a 15 code is this problem

[This message has been edited by uhlanstan (edited 11-22-2007).]