1991 4Runner V6/5-Speed Manual 4x4.

My truck is now at 317,000 miles. Still has original motor, never rebuilt (that I know of). Still has most of its original horsepower; doesn't burn or leak anything; and still gets about 16city/19highway with 31x10.5's.
I use the truck mostly as a daily driver but sometimes I get to do a little 'froadin.

Anyhow, yesterday I noticed the engine was idling really high. Like about 1300-1400rpm.
Normally idles at around 800-900 or less, I believe.

Haven't noticed any other changes, just the high idle.
No warning lights, oil and temp are OK and the truck seems to be running normally.

Any suggestions on what it could be?

Thanks

When was the thermostat last replaced?

There is a relationship between coolant temp and idle speed. If the t-stat is not opening/closing properly, that can be a cause.

There is thermo wax that controls a valve in the throttle body (TB) depending on coolant temp. Another cause can be plugged lines to/from the TB. Sometimes, the thermo wax & valve can be bad; like if the valve stays open.

For a temporary fix, you can always adjust the idle speed down w/ the screw on the TB.

my 92 has a high idle too...it was from me disconnecting my battery about 2 months ago...still in the 1200-1400 rpm idle range...some days it'll go lower to normal like 900 rpms or less....not sure why mine is doing it either...

time to check my t-stat then thanks for the info. i have been idling at 1300-1500 for a while now but every so often after getting off of a long stretch of highway or starting when the engine is warm it will idle normally. that is the only time though, anyway time to check into that, thanks.

2nd the t-stat... But another couple q's -

How does the temp look when idling for extended periods?

How old is your water pump?

Thanks for all the replies folks.

I just replaced the Timing Belt, Water Pump and T-Stat about a year ago. Used all NAPA Parts. The truck never runs hot.
Matter of fact, I just changed the oil today, then let it sit and idle for about 30 minutes while I tried to locate that stupid Idle Adjust Screw everyone keeps mentioning and the temp never rose above about 1/3.
Can anyone give me a better idea of where this screw is at?
This is a 3VZE/Manual 4x4.
It's not where my crappy Haynes book says it should be.

If it remember correctly, it is faces the front of the vehicle on the throttle body.
Black, slotted screw.

I think your t-stat is not closing all the way. I had an OEM t-stat go bad after only 6 months before. My temp guage needle is always a little left of center when it's all warmed up.

Thanks Code33, that's the one I thought it was but I couldn't get a screwdriver on it. Had to go buy a 10" driver to reach it.

Problem is, the screw was already adjusted all the way in. I could only turn it counter-clockwise and that made absolutely no difference in the idle speed at all...
Possibly another screw?

Also, when I said the temp ran at 1/3, I really meant that it is sitting just below halfway and never really seems to move from that spot once it's warmed up. Drove it around some today and kept a close eye on the temp.

If it is the T-stat, is there a way I can test it to be sure without actually taking the front of the engine apart (again)?

Thanks

Still having problems with high idle.
I've been keeping a close eye on the temp guage but have not noticed anything unusual.
Warms up with no problems, even in cold weather, and the needle stays pinned at just below half-point of temp guage once engine has warmed up.

I really think t-stat is fine.
Is there anything else that could be causing this? Possibly a bad sensor of some sort?
Maybe if I reset EFI computer or something?
I'm going to check for any engine error codes today, even though 'Check Engine' light is not on.

Any help would be appreciated.

The only way I know of to test the T-stat is to remove it and hang it into a pot of water. As the water begins to heat up and boil, it will open up. Then you watch to see if it closes when heat is removed.

It sounds like someone has messed with the idle before as turning it counter clockwise (out) is suppose to increase overall idle speed. It could be that there is something wrong with the thermo valve in the throttle body.