Intermittent High Idle

[acschilling]

I'm having an idle issue. My 92 5 speed had a wicked high idle, like it would hang at 2000 cold and slowly dropped as it warmed up. Changed the coolant temp sensor, thermostat and fuel filter and now it'll randomly idle at 1500. Sometimes it's normal, sometimes it'll get that cruise control feeling when you let off the gas (that's when I know high idle gremlin is back) and idle high at when1500 I'm stopped. Seems more of a cold weather occurring phenomenon now. If I stop and shut it off then restart it'll idle down around 1000. And the speedometer just went crazy yesterday... Jumps everywhere, and will say I'm doing 75 when it's maybe 45 or 50 I'm actually doing.

For context I had the high idle issue last summer. Replaced thermostat, IAC, alternator, battery. Coolant temp sensor was what finally cured it last time (18ish months ago).

Anyone else cure random high idle issues? And isn't there a speedo sensor somewhere? Transmission? Is there more than one?

I appreciate anyone and everyone with insight!

 

[alaskan155]

maybe a vaumn leak, while the engine is cold start spraying the starting fuid around the vacumn lines and intake gaskets and see if the rpm changes.

another thing to check is the clutch pedal switch, it might be bad,
if memory recalls the manual ecm will hang/delay the rpms from dropping to help with shifting(might not be it but worth checking)
How to: Clutch Switch Bypass

speedo is a cable in the tailhousing that runs up to speedometer. (mechanical), probally just needs taken apart and lubed.

other things clean the MAF, and how is the idle with the IAC unplugged? i had some of the parts store ones go bad after a year....

and what condition is your throttle body in, i know with my 94 with 241k the throttle body itself is shot and the shaft is becoming loose. also any codes?