High idle problem

[patdttr225]

Hello Group,
Would a bad Mass Air Flow Sensor make my 91 Ex. idle higher after a long drive up some grades? It doesn't always idle higher. What other components affect the idle?

Thanks,
Pat Dexter

 

[88vert]

Might want to check your idle air control vavle

 

[MrShorty]

I could be wrong, but I seem to recall reading somewhere that, when the engine gets hot, the computer will bump up the idle to help cool the engine down. May not apply to '91 explorers, I'm not sure. Anyone check me on this?

 

[410Fortune]

With a high idle first thing to check for is vacuum leaks.....

Then the IAC valve, or idle air control valve and the MAS sensor should be cleaned (do a search)

I have $10 that says our lower intake manifold is loose and you need to toghten it back down, or replace the gaskets. very common problem, especially on older Explorer's (pre 94). A loose lower intake will cause a vacuum leak.......

Either way do a search on these boards for:

IAC
MAS cleaning
Lower intake
and
vacuum leak

I have seen about 6 lower intakes that were finger tight at best, including my own. 10 minutes with a 10mm socket and a 1/4" drive, and blamo! problem solved (temporary fix, gaskets should be replaced)

 

[patdttr225]

Thanks everyone for the advice. I will check for vacuum leaks. I didn't think about that because in the past, vacuum leaks made my cars idle rough. The fast idle must be from the computer making adjustments, who knows.

Pat

 

[TPLYNCH]

Originally posted by MrShorty
I could be wrong, but I seem to recall reading somewhere that, when the engine gets hot, the computer will bump up the idle to help cool the engine down. May not apply to '91 explorers, I'm not sure. Anyone check me on this?

This is true. I believe it applies to all years.