Hello all, my '91 legacy engine has an intermittant high idle and wanted to see what the Forum thought with suggestions: A few facts -

 

MAF, IACV, PCV all cleaned - IACV was very much the first gen style, not dirty at all but cleaned anyway

 

I reset ECU which seemed to work but, weather was cooler so hard to tell

 

Idle situation seems to happen on a warmer day, idle can climb as high as 1800rpms, fan kicks in although engine temp gauge normal

 

I was able to clear idle the other day by blipping throttle where it did drop down

 

No air leaks evident and this high idle seems very intermittant, it starts to climb on a warmer day in traffic and usually will not clear by blipping throttle

 

I wonder if IACV has enough play to bind from time to time which increase when engine/ambient temps are warmer?

 

Any thoughts? Suggestions?

on that car, there is a separate Engine Temp Sensor whose wiring or guts 'MIGHT' fail in such a manor the ECU is told the engine is cold.

 

but, 1800 is quite high. Not sure a new temp sensor would cure the problem.

 

you might try tapping on the MAF. I have recently read of some MAF issues with internal connections.

 

is the CEL on? any blink codes available?

 

maybe someone else will have an idea.

Edited April 14, 201510 yr by 1 Lucky Texan

Thanks, this engine is a transplant into a vanagon but I was not getting enough feedback in that forum so I appealed to this forum for more specific engine advice. No CEL installed at this time unfortunately -

Situation seems to have leveled out somewhat, I can blip the throttle and generally clear this problem so I am guessing that this problem indicates a sticky IACV that acts up when hot? Anyone?

This might be something in your intake as well. Heres what you can do. 

 

http://www.ultimatesubaru.org/forum/topic/118540-idle-air-control-valve-cleaning-problem/

 

Take a look at that thread. Any type of detergent (even ATF will do) and pour it down the tube into the IACV. I didn't have this problem like you did, but this method worked wonders for my vehicle. Give it a shot maybe? Worse you can do is clean out your intake and valves.