Hanging Idle

[88Slowbird]

EDIT: fixed see reply below

What else will cause a hanging idle other than the TPS or vacuum leaks?

If I blip the throttle quickly it will come down to 1000 RPM but as soon as you press the throttle again it will stick at 1500-2000 RPM

The throttle body is clean and it always closes all the way so I don’t suspect anything is hanging up physically

TPS has been sweep tested no dead spots and it’s set to .85 and I’ve verified it always goes back to .85 when the throttle is shut
(I don't believe it needs to be exactly 0.95 or 0.99 like some say it just needs to be below 1.0)

I cleaned the IAC and did a proper base idle reset but that didn’t seem to help

0 Vacuum leaks I've inspected and sprayed brake clean on every line and all around the intake with no change

tested the ECT resistance hot and cold and its in spec

tested the VAM VAT sensor and it's in spec (VAM air temp sensor)

VAM possibly causing this? ECU caps bad?

[scenario]

Just last month or so I replaced BOTH the TPS and the IAC. The IAC was from Rock Auto and a very quality unit Walker part # 2152003. This fixed my issue 100%. I tested my old TPS and it was out of spec on the low side of the voltage. I would def replace BOTH. It is nice to have the idle working poroperly now

[gbeaird]

Hmmm, $40 for an. IAC. Maybe I should grab one, too. The idle on our 86 seems kinda low.

[svono50]

Check your ECT sensor, the one top/center on the lower intake. When they go 'bad' they tell the EEC it is very, very cold and the EEC's reaction is a high idle condition...ask me how I know. Otherwise you could disconnect your IAC when it is up at the 1500rpm mark and see if your idle drops...because it should if the IAC is sticking open. Throttle linkage slop can also cause this as well. Mine has been 'sloppy' for years and I have just been too lazy to address it, since a quick blip on the pedal brings it down at a light. YMMV.

[88Slowbird]

ended up figuring out the throttle body blade wasn't closing all the way

cleaned the throttle body and greased the linkage now it doesn't stick

I'd post a video but not sure how to here