81 FI Fast Idle 1600RPM out of ideas

[tima01864]

I thought so.

[ORFORD2004]

My book said:
Turn the idle speed adjustement screw in all the way.
Adjust throttle stop screw to obtain 700-800 rpm.
Hold stop screw and tighten locknut.
Adjust idle speed screw to obtain 800-900rpm.
Check the throttle plate switch adjustement.

[sclebo05]

Replaced O2 sensor (very old unit, almost completely crusted over), which was interesting due to the cross-threading that the previous owner performed. No change, just wanted to verify another component.

Again, I'm still in the 1100-1400 rpm range. Car idles and runs great, just has a fast idle.

Should I look at ignition timing advance? I'm really lost on this one.

[tima01864]

When had the timing light on the crank, Revving the engine marks did not come back to 10 degrees. Sticking advance. I replaced the distributor. Positive results, Still the idle is around 1400 rpm.

[DanD]

Check the air inlet for the distributor advance, which is just under the larger crankcase bypass hose at the throttle plate.

Check and make sure the advance diaphragm isn't perforated.

[RRoller123]

Edited. My mistake, thinking of a different part. Duh.

[rridge]

Check that the Throttle Position Sensor (TPS) is working and is properly adjusted. The TPS tells the ECU that the throttle is fully closed so that the ECU can go into its idle program. Oxygen sensor is cut out in the idle control loop.

[Odoyle]

Two things I have done recently that lowered and smoothed out my idle 1. O-ring on the idle adjustment screw can be replaced with a new o-ring from Midwest Bayless and 2. Following factory procedure for adjusting idle speed as stated by ORFORD. 3. Making sure the vapor canister isn't missing the small black cap that restricts air flow on the top of the canister.

[RRoller123]

Check that the Throttle Position Sensor (TPS) is working and is properly adjusted. The TPS tells the ECU that the throttle is fully closed so that the ECU can go into its idle program. Oxygen sensor is cut out in the idle control loop.

With the engine off, advance the throttle plate by hand, and listen closely for the "click" as the switch engages. It should click almost immediately after the throttle leaves its stop position.

[76was124]

I have an 81 which had the same problem...went through all these same steps five years ago with no improvement below 1100 RPM without causing other issues. Somebody finally gave me excellent advice. Quit worrying about the high idle and just enjoy driving an otherwise perfect car. In fact that might have been your advice RRoller

[tima01864]

ind of agree with that, I have done about everything. Some day it will slow down, Happy with 1100rpm's

[RRoller123]

Mine idles lousy below about 1100. I just accepted it after trying everything. It never comes even close to overheating, even in Summer traffic. It was also Csaba's advice at the time to stop worrying about it. He is right. I do have a lightened flywheel, large valve head, adj valve wheels, 274 street cam, etc that effects this sort of thing. I run dist timing a little more than 10, like 11 or 12. That raises the idle, but below 10 the engine runs just awful. I also think valve timing will effect this greatly too? I need to recheck mine, I think the adj wheels may have slipped a little, because it is just not quite as peppy as it was, and compression is still good, unchanged at about 145-150 for all.