‘01 Tacoma 2.7L 4wd high rpm in idle

First off, this forum is awesome and I’ve found a lot of help through posts on here, but I’ve never posted myself. So if anything is wrong with my post, or post location, please let me know.

My truck was recently misfiring, no code, but I’ve had a misfire before so I knew what it felt like. I went to replace the spark plugs and noticed oil in cylinder 4. The tube seals were dry rotted so I replaced them along with the spark plugs. Also put a new valve cover gasket in. After I put everything back together, I started it up and it was sitting at 1500-2000rpm in idle. First thought was the throttle body so I took it out and cleaned it thoroughly with Seafoam carb cleaner. Didn’t fix the high rpm. Played with the idle adjustment screws to no avail. There is the slightest crack on the end of the breather hose and I ordered a new one that comes in Monday.

One thing to add: The butterfly valve is slightly open and I can manually turn it closed, but it goes right back after I let go (with engine running). This is obviously the issue, but I’m not sure what could be causing it.

Any other ideas or possible things I could check? Could the cracked breather hose cause that dramatic of a change in idle? Any advice is welcome. Thank you.

 

Be careful cleaning the throttle body, there is a "iac" valve under there. When you clean the throttle body all the gunk go down and make that valve gummed up.

The three things I see on this forum pop up alot for idle issues

1.) IAC valve is dirty, needs to be serviced.

2.) ECT sensor ( There are two, i believe the one on the back of the block is responsible for idle)

3.) Vacuum Leak

In your case, I would inspect #3 first, you didn't mess with the IAC or ECT prior to the valve cover, I found my vacuum leak with a small blue can of propane and a rubber hose. I waved it around the hoses and watched for my idle to change.

 

Is the idle still high at normal temps? Or just cold?

 

I plan on letting it run long enough to let the temp rise tomorrow to check that.

Edit: makes no difference in the idle whether the engine is hot or cold.

 

Thank you for the advice. I’m not sure I understand what you mean with the propane and rubber hose. If you could elaborate a little more that’d be great. Also, if the IAC valve does have gunk built up from cleaning, how should I go about servicing that?

Edit: found a video explaining the propane method. I will be trying that.

 

I just took mine off a cleaned with car-b-kleen. Use good gasket putting back together.

 

Update:
Took it for a spin just around the neighborhood and I noticed a few things that could help with diagnosing the problem.
First off, the coolant and oil levels are good and no noticeable leaks. Battery is new. Temperature gauge works properly and engine temperature is normal.

Notes on how its running:
Rpm is relatively better in drive/reverse (not in neutral), but still a little high. I have to slam the brakes even at low speeds to stop since its pulling more than normal. After letting it sit for long enough, the idle will drop from 1500+ rpm down to 1250 rpm. I can pull back on the accelerator pedal (not sure if that's normal) to lower the rpm down to the desired 750 rpm, but it starts to misfire below 1000 rpm. If i press the accelerator again (in park) it will raise back up to 1500+ rpm and stays there unless i pull back on the pedal again. While in drive, the engine is randomly misfiring at lower speeds. Makes no difference whether the engine is cold/hot. Shakes more than usual when shutting off the engine.

Still no codes. I got this code reader 6 months ago (

$18 MOTOPOWER MP69033 Car OBD2 Scanner Code Reader Engine Fault Scanner CAN Diagnostic Scan Tool for All OBD II Protocol Cars Since 1996, Yellow

MOTOPOWER MP69033) and I've never had it return a code on my truck before (possibly not compatible). There is a load value percentage option in the code reader. Is this relevant/useful?

Also, taped the end of the breather hose to try and seal a possible vacuum leak and it made no difference (new breather hose comes in Monday). PCV hose has no cracks. Cylinder 4 ignition coil boot that goes over the spark plug was loose and I could easily take it off.

If you have any other advice or what direction to move in next, it would be greatly appreciated. This is my daily driver so its been tough not having it.

 

Maybe check your tps. Mine is adjustable and I think it is set at around 14.1% at idle. When mine was acting wonky I took it apart and cleaned up the rheostat strips and contacts, that fixed it.

 

So i found this video on adjusting the voltage for the tps. https://www.youtube.com/watch?v=ukQMQPh0HmU So basically ~0.45V when closed and ~4.5V when open on the middle wire. is this what you adjusted or are you referencing something else? If not, how did you measure the percentage? Also, are you talking about the strips in the tps connector?

I am going to go ahead and test that voltage. Might just get a new tps if its acting weird. They're only like $14 at auto zone.

 

I used a knife to pry the metal cap off then cleaned of an tarnish. After that it works smooth. I mean when testing voltage it didn't have dead spots. I got a trq aftermarket tps from 1A auto that seems to work okay but reinstalled the oem. I'll keep the trq for backup. It is recomended to replace with oem. Lot of bad reviews for aftermarket stuff. I'm using torque-pro app with a BAFX obd2 interface. I just look at the throttle position reading while adjusting the tps. Seems to work just the same as using feeler guages.

 

If your throttle is not cable operated then you may not be able to adjust, only reset by pulling fuse or disconnecting battery.

 

I will try this but it’ll have to wait 2 weeks as I’m going on my honeymoon to Italy. My throttle is cable operated so it should be adjustable

 

Sounds like the throttle cable is too tight, being able to pull your pedal up doesn't sound normal to me. Not sure about the misfiring under 1000 though.