So i just bought my first fiero an 87 2.5 4cyl 5 speed. It was sitting for about 5 years so i got it running after changing all the fluids and other stuff such as plugs and wires new gas. So ever since I got it running ive had a problem with it idling to high after starting it up it idles around 2 grand until the engine is up to operating tempature. So my first thought was an vaccum leak. I have searched every inch of the intake for a leak and can not find one I have rebuilt the entire throttle body with new gaskets, put in an new idle air control motor, new thermostat, ect sensor and even a new pcm. So im baffled about what it could possibly be. If anyone has had this problem let me know some fixes it would be much apreciated. Thanks Dustin
GM programmed the cold idle pretty high on the Fiero engines.
If your idle starts high when cold, and reduces to about 850 - 950 RPM when fully warmed up, that pretty much means the IAC, ECM and CTS are working right, or at least rightish. A non-functioning IAC would idle slower cold and higher warm. The ECM isn't really going to mess up the idle speed, if it is working. The CTS must be indicating to the ECM when the engine is cold, resulting in the cold idle, and once the engine warms, again must be reading rightish since the idle reduces. If you really want to know exactly what the ECM is doing you can get a scanner cable, and use TunerPro RT on a laptop to get the actual readings. Again, my guess is they are at least working about right. btw, I sell the scanner cables here - http://www.reddevilriver.com/aldl.html
TunerPro RT can be downloaded for free at tunerpro.net
----- The solution if you really want to fix it ----
If you wish I can supply you with a reduced cold idle speed chip for your ECM.
Jumper pins A&B on the ALDL port behind the cig lighter panel. Turn ignition key to ON but do not start. Walk back to engine and listen for "click, click, click" as IAC is driven fully closed. Wait 30 seconds then remove IAC electrical connector. Now walk back and turn ignition key to OFF. Remove jumper on pins A&B on ALDL port. Walk back and reconnect IAC electrical connector. Now the car should start and idle normally.
On my '87 when very cold it would idle very high for a minute or two then slowly idle down. The warmer it was outside the lower the cold idle upon start.
You'll still want to check into what phonedawgz mentioned and scan it for proper coolant temp sensor operation as the idle has a direct tie into that and if it's biased toward the low side it can cause a higher than normal idle. There's also the very real possibility that having sat for 5yrs and you not knowing the history prior to this that you have a failing tachometer that is reading several hundred rpm higher giving you the impression the engine is idling to high after warm up when it may be on point.
dont know if it makes you feel any better but my 87 2.5 will idle 2000-2200 when its cold but after it warms up it drops to 800 or so. it does take it a while to warm up. i searched all over for a vacuum leak but havent found one.
I am wondering as well. 2200 when cold and takes about 4 min of running that high before it will switch and go down to 800...pretty drastic change. it is the last think left to fix on it (86 2.5). TB is bolted down tight. Egr is unplugged because when it gets vacuum and is working the engine runs poorly- starts chugging. So I just plug the vacuum line to it. All new vac lines and tested canister and it is not leaking.
The best way to find a vac leak, is to get a small hose that is 4 or 5 feet long an when your motor is running put one end to your ear and the other end move it all around your vac hose's an the motor you will hear any leak's on your motor! It work's an it's free or very cheap. Good luck
87+up EGR is not Controlled by ECM but GM program Ignition timing to expects EGR flow and Engine can knock w/o a working EGR valve.
When cold is NORMAL to get high idle when ECT sees low coolant temp. 0°F and starting cold then expect 2000+ RPM when AT is Park/neutral or MT out of gear etc. ECM is trying to make sure engine won't stall. Should slow idle to ~1100 in a few minutes then to normal, ~900, when engine is warm.
Idle speed is 1000 RPM when ECM scan tool is attach. ECM can run w/ scanner but can affect Idle speed and other settings.
TSB on PROM... See my Cave, PROM TSB notes If you have high idle at odd times then maybe you need update PROM. Most cases I've seen... Most high idle is vac leak etc. New PROM versions can fix the knocking, mostly ~half throttle w/ some engine loads.