About two months after I bought my Fiero, the service engine soon light came on. It only comes on when I sit at a light for a few minutes and eventually goes away if I wait, or goes away immediately when I start to accelerate. Also recently whenever I start my car for the first time in the day, no matter what time it is, it revs up to 2000 then goes down to 500 then finally settles around 1500. When I decided to track down the problem I plugged in my schools code scanner into the car and it picked up the EGR System code, IAC valve code and a rich exhaust code. I replaced my EGR (it had nearly rusted off anyway) and my IAC. That seems to have solved the problem of the light so far, but when I start the car for the first time today it when to 2000 then to about 50, much lower than before, and then finally idled at around 1300. I believe I installed the IAC right, I moved the pindle to the same position as the old one and I did the reset procedure by driving at 64 kph. But I don't know what caused it to start bad again. Please help. I have a 1988 Fiero GT 5spd, near stock. Thank You.

Here's a stab at it, guys like Dr Fiero might know better.   I can only hedge on this based on some experience from my carburated car days and mid 70's pollution gadgets.

The starting at 2000 rpm and settling down at around 1300rpm when the engine is cold is normal.  The 1300 rpm is high idle and it is set to warm up the car faster to get the catylitic converter to operating temperature as quickly as possible.  When you start your car, the fuel pump comes on first to prime the injectors so when the car turns over, a dumps fuel into the cylinder so start up is slightly rich.  Once the car warms up, your idle should settle down to normal around 800rpm. 

Your idle dropping down to 500 rpm sounds troublesome because at 500 rpm, the engine should be very close to stalling.  It is possible that the fuel is not atomized enough and hence did not mix with air properly to combust.  If that is the case, your fuel injectors might need servicing.  (just a guess)

Not that I know of. The exaust is original y-pipe and up. I don't smell any leaks or hear any. I only get the light after the car is warm and is sitting at a stop light for a while. It goes away after I start to drive or sometimes goes away by itself. Occasionally the light comes on when going up a long hill at 50km/h in third but, I've had the car for a little more than a year now and it has only done that twice. Once last year and last week. Thanks.

88 are extremely hard to pass if they are not in OEM condition.  I posted my 88 Aircare spec sheet and in some classes, the 88 must be 10x cleaner than an 87.  Yep an 85-87 V6 Fiero's can put out 10x the emissions of an 88 even though they are basically the same car.

You will need your Cat converter and EGR system working perfectly.

As for the issues you are having.  I would probably start with the Injectors. 

If you are comfortable doing a little wrenching around your interior and getting access to your ECU, or more specifically, your diagnostic cable, you can read your trouble codes through the blinks of your SES light.

I am practically a chimpanzee and I did mine with VERY little difficulty, my center console is not bolted down either mind you, but it's VERY easy to do, and will tell you exactly what codes your engine is throwing, IE precisely what your engine is doing that your ECU doesn't like.

Here is the page I used to diagnose my MAP sensor issues when my SES light was bothering me, read it over a few times and consider doing it.

http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes - http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes

The CLub Scan tool is in the front trunk of my 88GT at every meeting if somoene really needs to use it.

I just did the code check and it came out with code 35 IAC. I just replaced the IAC within the last couple months. When the code was set, the conditions were no different then with the old IAC. I was sitting at a light for a bit and it set the code. The car was warm and I had been driving it for a while. Now that the weather has cooled down, my car starts fine now. I read what it said on http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes - http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes  . I think my idle speed is too high when the code is set and it says to check for vaccum leaks. Which vaccum hoses am I looking for. Should I clean the old IAC and put it in to test or should I just deal with the new one in there? Thanks

Check your EGR valve, it may be leaking, sticking, or like mine, completely rusted off.

Then check all your little black plastic tubes snaking through your intake manfold runners, those are usually suspect for breaking and cracking as they get very fragile when exposed to so much heat.

Hope that helps.

None so far except that I found a crack in my EGR vac. line. I was going to go tomorrow to get some model airplane fuel line and some shrink tubing that my grandpa uses on his model airplanes. I heard somewhere that the fuel line works good to fix a leak but I don't remember where. I couldn't find anymore vac. leaks unfortunatly. Are the little rubber fittings that connect the vac lines to the egr, and other things, prone to causing leaks? Some that I found seem to have some hairline cracks but dont seem very deep. Thanks.