High Idle

My truck recently started idling high. Currently idles at about 950-1000 rpm in park/neutral and about 700 rpm in drive. Cleaned the IACV and throttle body a few months ago, but the problem didn't start until recently.

I'm thinking vacuum leak, TPS, or possibly a bad IACV.
Thoughts?

Truck is a 2000 3.4 auto BTW.

 

check for cracked vacuum hoses with some carb cleaner . When you cleaned the throttle body did you remove it and The IAC? Did you replace the gaskets? Spray carb cleaner around those areas to check for leaks.
Good Luck!

 

Yes, removed throttle body and IAC and replaced the IAC gasket. Didn't replaced the throttle body gasket, it looked fine.

The vacuum lines are looking a little old and weathered, so I'll check those next. Any line in particular that might be suspect?

 

Pretty much all the vacuum lines, if you can see all the lines are getting old they would all be suspect.

 

If you don’t find any vacuum leaks, look at your butterfly in the throttle body.

There should be NO gap between the butterfly and the throttle body wall,
A gap can be created by a throttle body cleaning after the carbon is removed.

This is what it should look like,

A gap will create a high idle

 

Update: truck was idling perfectly for the first half of the day and then jumped up to idling consistently at 1200 rpm for the rest of the day.

Checked all the vacuum lines with carb cleaner, didn't notice anything. Might try soapy water next. I inspected all the rubber lines and most are dried/cracking where they meet fittings.

When I had the throttle body out I didn't notice any gap, but I can check again.

 

If all those are good it’s narrowed down to probably one of these two items.
Idle position sensor
Idle control valve

 

What's the likelyhood of it being the IAC even though I just cleaned it? I've actually got a spare new IAC laying around somewhere but it's a cheaper Chinese unit so I'm hesitant to put it in.

Where is the idle position sensor?

Also, tried sprayed spraying some soapy water on vacuum lines today, didn't notice any bubbles. But I would be surprised if these lines are holding vacuum as they are pretty dry rotted.

Started the truck up once today and it idled perfectly, around 700 rpm in park. So the issue is definitely inconsistent.

 

On the throttle body.

 

throttle bodies dont last for forever... grab the bellcrank and slide it axially and check for play. If there is play the throttle blade will not sit correctly in the bore and the idle will be high. The next time the blade is moved it just might sit in a "normal" position. Depending on how much slop there is between the TPS, the throttle shaft and the age of the TPS, this might be contributing to a higher then normal idle. The blade is cocked open just a little, the TPS recognizes the throttle is not closed and the fuel injection / trims are adjusted, the spark timing is advanced etc. etc. to this throttle position.

 

This seems somewhat common in first generation Tacoma’s? Mine doesn’t idle too badly in neutral or park, but it’s definitely at about 500 RPM

 

It is pretty common. Mine actually idled really low for a while, especially in drive. So I cleaned the IACV and it idled perfectly for a few months and now it's idling too high.

 

Update: truck has been idling fine the past 3 days, no high Idle. Will keep an eye on it and see if it starts acting up again. Any ideas what would cause a temporary high Idle? Bad gas possibly?

 

IAC valve. Mine did high Rpms when I first got it. It was above 2000 RPMs. Stopped when I replaced that. 3 years ago to now the RPMs are at a little above 500 maybe 600. Buy the one from Toyota.