I have an 87 GT (2.8 with 73000 miles) with a "Hunting Idle" that I have been troubleshooting for a while.....

It is a car I bought last year and I have replaced many parts. When I got it the idle was high and after replacing some sensors and filters we found the EGR Tube fractured at the Manifold. Solved the high Idle.

When we changed the plugs one of them was broken and badly burnt. With the new plugs in my idle went rough with a Hunting Idle and then the car quit. We replaced the coil and I ran decent . A day or two later - it quit on the road and would not restart. I then replaced the Distributor with a new one and it runs good - with the exception of the remaining hunting idle.

It idles cold around 1000 rpm and once it begins to warm up it tries to drop. As it drops it quickly pops back up in a 50-100 rpm range as it tries to drop. Once it is warm it drops to 900 with a variation of @50 rpm -but every few minutes will drop too far, act like it may stall and pop back up to 1000 or even 1100 rpm. It then repeats this cycle. It runs on the road fantastic. Under load you would never know there is an issue. Occasionally, when I coast into a stop sign or light I will find it has stalled or it will stall just as I stop.

I would appreciate any suggestions. I know this is a common issue.

The car has a new Engine Temp Sensor, IAC, O2 Sensor, PCV, MAP Sensor, Thermostat, Temp Gauge Sending Unit,

It sounds like a throttle position sensor. I notice that is not in your list. I have heard that this is a common issue with the sensor at its stop. I have a very vague recollection from when we got our 88 that the TPS caused exactly the issue you describe. It was way long ago, so my memory is cloudy on this one. I seem to recall that getting a dead spot at the idle position is a common failure.

I would try to replace the IAT/charge sensor and TPS. It's also worth checking the valve lash adjustment if it hasn't been done, and compression test.

But to honest I haven't seen any 2.8s that didn't have a hunting idle issue to a certain degree, I think I once heard that only 7730 ECM upgrade will make the 2.8 run perfectly.

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86 Fiero GT 4spd - L67 swap: VS cam, GenV. Needs exhaust (ETA 9/13) Build Progress
98 GTP - Some mods

Preform the idle stop screw adjustment procedure and it will solve your engine stalling when coasting to a stop problem.

It might also reduce the low low drop in your idle speed but it won't solve your hunting idle problem.

I don't think it's your TPS. It would be interesting to see what a scan of your engine is doing when the idle hunts.

btw, I did the 7730 swap to fix mine.

[This message has been edited by phonedawgz (edited 08-09-2013).]

Ok.

Today I got a check engine light. Did not happen under load, when coasting on the highway. Pulled over and restarted and it reset. Came back a few minutes later.

When I got home my uncle and I pinned the ALDL and got the code. It was for the EGR Valve. I took the new EGR off of my father's GT and put it in mine - problem was still there.

Started looking around the EGR and over to the solenoid and found the issue. There was a vacuum hose on the solenoid that the end had failed/dry rotted and was no longer effectively connected. We drove the car right to Advanced Auto and bought a piece of new vacuum hose and put it in. Car was still "hunting" when I pulled out of Advanced Auto - but 5 miles later when I got home the idle was dead set right where it should be. No more hunting, or stalling when shifting into gear. Lucky find. I have actually been looking for this for about a month, so I am greatly relieved tonight.