High Idle after Valve Cover Gasket change

I quadruple checked connectors and hoses, but still could have missed something. Only other thing I can think is that I clogged something in the throttle body when I sprayed some cleaner in.

In Park its at 1500, in Drive 1000. Normally 1500 is normal when its cold, but it didn't fix itself later. And actually when it was cold it was normal...its backwards

Any suggestions?

 

Sometimes it takes a while for the computer to readjust itself after cleaning the throttle body. Drive it for a couple days and report back.

 

Did you use new plenum gaskets? They can't (shouldn't) be reused.

Also, like was said, high idle is normal if the ECU has been disconnected for a good while. It will relearn.

I put in an entirely new Throttle Body and it took about 30 minutes of idle and driving around for it to get back to its correct idle. Now it's perfect.

 

No they were recently replaced, look new. And I've not replaced the ones on my tacoma before, which are old and crusty, and it never had this problem.

And same on the ECU. The ECU "relearns" timing and fuel trim; I don't know what it does in relation to the IAC, but I've never had a battery reset do this. Guess I'll just keep driving for now.

 

I would drive it for a bit. If it persists, do the carb cleaner trick and spray around the vacuum lines and plenum and see if the idle changes due to a vacuum leak.

But you're right, low idle at cold then switching to high idle is kind of backwards. I would suspect the IAC or the MAF or the TPS I guess. When's the last time the TB was cleaned thoroughly? I know I was not able to clean mine properly unless I removed it from the car. 250k miles of neglect and it had a ton of gunk. Enough gunk that just cleaning it on the car would have probably blocked some of the small airways.

I ultimately replaced the entire thing and it fixed my idle problems (which included low idle and surging). But on my car, it is a different setup. There is no IAC and the TPS wasn't sold anywhere at the time. The TB was a complete, "unserviceable" unit which had the TPS, Pedal Position Sensor plus motors for adjusting the throttle all included.

 

I actually replaced the TPS and purposefully neglected to clean the throttle body at the time, ironically because I thought it might cause a new problem. MAF was cleaned though.

If it progresses I will just remove the whole thing and give it a good scrub.

One other notable is that when I took off the air intake for this job, I noticed the tube for the IAC was disconnected. I kinda figured I nudged it out on the way, but maybe I'll see what disconnecting it does..though no idea why that would work.