On an easy drive last night the engine suddenly lost its ability to idle. Actually, it would barely idle, maybe 300 rpm, but I suspected it would die if I didn't keep my foot lightly on the pedal. Car has always previously idled well, 650-750 rpm. Put my ALDL Scan and ALDLDroid on it this am, and I'm showing .392 volts for TPS with foot off the gas. BTW, alternator voltage is showing 13.1 volts at idle...seems low. Fuel pressure is good.

Otherwise, the car runs well above idle.

Thoughts?

Thanks

Ernie

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'87 Fiero 4.9 5-speed

[This message has been edited by Warlordsix (edited 07-19-2020).]

If the TPC reading is 1v or below it should be within normal range. I suspect that your idle air motor may be bad. That what is what it was on my 4.9L. If you decide to replace it then use a depth gauge ruler or carefully measure the projection of the screw to make sure that the intitial adjustment is close. That will give you a good starting point or maybe be the sweet spot for a good idle.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Thanks, Dennis. It's idling great now. I disconnected the battery for awhile, reconnected it, then started it up and shut it down a few times to go thru the idle learn process. Idles great now...just like it did before. Explanation? Dunno. Something spurious. I'll just keep my eye on it.

Thanks, again.

Ernie

The position of the throttle plate (and thus the TPS) at idle may have changed. Why? Good question. Maybe the throttle body is dirty, or is getting sticky at low throttle. Or maybe the idle screw (if it has one) backed out a bit.

In any case, the ECM expects a certain voltage range at idle (which is set during the idle re-learn). It gets confused if idle voltage is outside that range. Also FYI, if you find and fix whatever caused the problem in the first place, you'll need to do the idle re-learn again.

[This message has been edited by Blacktree (edited 07-19-2020).]

Thanks, Blacktree. I think you might be in the Central Florida Club, no? I am, too. Have only been to a few meetings, but will attend more frequently in the near future.

Ernie

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'87 Fiero 4.9 5-speed