Hi all.
I've suspected a dirty IAC for a while now because of occasional high/floating idle (1000-1500).
1992 525i with 270K miles on it.
Recently the car has been running well. Idle has been down at normal - ~ 700. (Although it failed smog again...thinking cats again).
I took a trip from SF down to Carmel Valley for some golf this week and on the way down, the idle again became high.
I've ruled out a vacuum leak because the high idle isn't consistent.
When cold, idle is normal (for cold start), but when at operating temp, it's high.
Before I pull it apart to clean out the IAC, I was wondering about the Aux Thermostat.
My aux thermostat got broken a few years ago so it's bypassed now. I have a new one but haven't installed it yet.
From everything I've read, the thermo is to keep the throttle plate from freezing in cold weather...something I don't need to worry about here in the SF bay area.
I got thinking though (dangerous) if the thermo would also act to keep the throttle plate at engine temp so it didn't get too hot in hot weather/driving.
So I have two questions that I was wondering if you could weigh in on:

- would a higher than engine temp on the throttle body result in a higher idle?
- is my assumption that the high idle isn't due to a vacuum leak correct since the high idle isn't consistent?

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