High Idle in Park

[Explorer94GV]

On my 94' Ex when in park i have extremely high idle. In the 1.5 to 2 rpm range. It sounds like you are stomping on the gas pedal. The fuel mileage has dropped badly. I just had the head gaskets done. I have been told that it may be the lower manifolds gasket. Also another unusual occurence now is after i drive the Explorer and then park it and shut it off. The radiator coolant starts to bubble back up into the coolant overfill. It fills the thing damn near to the top. It runs fine not overheating or anything it just is quirky. Any info is appreciated.

 

[MrShorty]

The coolant bubbling up into the overfill sure sounds like it's overheating. And, in many cases, when the PCM seesan overheating condition, it raises the idle speed to try to draw more air through the radiator to cool it down.
I'm not sure how the '94's are set up, but my '92 has two separate temperature sensors, one for the dash gauge and one for the PCM. Perhaps the mechanism that controls the dash indicator has failed so you just can't see that it's overheating.

 

[dogfriend]

High idle could also be caused by a vacuum leak (you mentioned the lower intake manifold)

Also, you might want to verify that the head gaskets are ok through a compression test - I had a truck that would expel brown foam from the cooling system after you shut it off - that was caused by a leaking head gasket

 

[AlaskanJack]

For the high idle check the back of the vaccuum tree. I had same problem and found that I had blown off a vaccuum cap on the rear of the vaccuum tree. Its in the back of the engine same side as the master brake cylinder.

Get a code reader and see if you can pull any codes.

 

[TPLYNCH]

If the computer senses an overheating condition it will idle the engine higher to try and cool down. Where is the temp guage reading when this happens? If normal, you may want to try cleaning the temp. sender.

 

[Maniak]

Check to see if the IAC is stuck..

When I did the tstat my idle came up (about 1500-2000 in park)...

I figured I goofed my lower intake (I did that at the same time)..

I left it for the night.. and when I got up in the morning I decied to rule out the easy things first.. I disconnected the IAC.. (I pulled it off and went to put in a solid piece of gaskett material)..

When I put it back on the idle was very low.. So I knew it was the IAC..

When I checked my IAC (closer inspection) I found that the plastic the t-stat came in ended up in the IAC.. (not sure how that happened)...

I took apart the IAC and removed the plastic.. now all is fine...
Just something else to check...

~Mark

 

[AlaskanJack]

When I checked my IAC (closer inspection) I found that the plastic the t-stat came in ended up in the IAC.. (not sure how that happened)...

Ha funny! Its weird how stuff like that happens. I was looking all over for my car keys over the weekend. After almost 2 days I went to retrace my steps and found the keys on the frame near the t-case where I had been working 2 days earlier. I have also found my wife's keys in the freezer.

We need to get a clapper for our keys!!