1998 3.4 High Idle Have Tried Everything

I have a 1998 Tacoma 3.4. and I have replaced temp sensor, IAC, TPS, MAF, and she has a fresh valve and timing belt job with all lines and hoses replaced so no vacuum leaks. 285 miles on it. It was idling high prior to all the work and still does. The position reads 7.5 and still runs around 1150. I have the idle stop screw almost all the way out to get it to idle that low. When I move the throttle to position 9 it is almost running 1600 rpm. Temp and everything looks normal to me. Posting the OBD2 info in case someone sees something I don't. Does this mean I need a new throttle body? There is no play in the throttle body side to side as shown on YouTube. Any help would be appreciated.

 

You have ruled out the throttle cable sticking and lube the linkage on the throttle body .

Checked for a cracked fire wall causing the throttle cable to bind.

best of luck

 

Welcome to TacomaWorld
http://maxbore.com/

 

Yeah the throttle body will wear over time inside where the butterfly valve is, and won't seal at idle causing it to run high. If you take the TB off and look through it up against a light you could probably tell for sure. Getting it rebored will fix it

 

It isn't a linkage issue the stop is screwed almost all the way up and you can feel it close. I was just hoping someone would point out something I was missing. I will definitely look into a re-bore.

 

Is there slack in the throttle cable where is comes out the sleeve? Try running it with the cable disconnected

That positive 6% long term trim is suspect at idle/no load/no vehicle speed. Thats a normal reading when cruising down the highway at 65-70 mph. Idling in the driveway it should basically be 0

Are you sure there's no intake leaks? Have you smoked it? Spray some brake cleaner around the intake and see if that +6 percent changes or goes down

 

I fixed a wore out butterfly valve with a washer in the linkage. Had to grind the washer down to a perfect thickness to get it to work right. Try pushing towards your firewall on the butterfly valve while the truck is running and see if it idles down.

 

I had smoke tested it before, and didn't spot anything, and I also sprayed some carb cleaner but never heard a change in rpm. I did just do a valve job and basically replaced almost everything when I put it back together. I will try it again with the OBD2 tool to see if it registers anything. Thanks for your suggestions I will keep you posted.

 

I should probably add I just got it running today! It has been sitting in pieces for a few months. Not sure how long it takes to get a proper trim reading. I literally have only taken it to the gas station and back home.

 

Ok soo update. I removed the the throttle cable and hosed down the entire engine with brake clean and there was absolutely no change. Prior to the rebuild I had smoke tested it and even replaced the ECU with a junk yard one that didnt affect the fast idle. So does that just leave the throttle body?

 

Did you use brake clean to try to detect a vacuum leak? Do not do this. Burning brake cleaner causes toxic gases to be emitted. There are more appropriate and safer methods to determine if you have a vacuum leak.

Have you considered replacing the vacuum lines? YotaShop sells a vacuum hose kit (KIT-1106) so that you don't have to hunt through all the parts catalogs figured everything out.

A few of the lines are impossible to get to without removing the intake manifold and the main wire loom (ref #s 17341T, 17342L, 17343F). I held off on those three until I did my valve cover gaskets, which made them easily accessible. I don't think they were leaking, but one of the smaller ones had split ends, so I'm glad I got it before it was a thing.

I'd so inspect the tension on your throttle cable. Mine was ever so slightly too tight, and resulted in a high idle. This can happen if you remove the two stopper nuts holding the cable in place, and reinstall it them in a different position.

 

Yikes...yeah use starting fluid to test for leaks. Brake cleaning fluid is nasty dangerous shit when it burns

Maybe the non-chlorinated kind is OK, I'm not sure...wouldn't want to risk it either way.

 

A small propane torch works as well. Obviously don’t light it...

 

As was pointed out to me, and reinforced by others, DO NOT USE brake cleaner through a running motor. At best, you'll destroy your cats and 02 sensors, and you'll expose yourself to toxic fumes which can lead to SERIOUS and DEADLY kidney/organ failure.

 

Check to see if your mass airflow values are in spec. If they are, then its either unmetered air getting in after the airflow sensor (could include the idle air control valve) or an exhaust leak. Hows your exhaust manifold looking? Many of them crack causing the ecu to belive it runs lean.

 

If everything else checks out its probably a worn out throttle body. Remove it and hold it up to light. If there’s any light on the sides near the pivot shaft it’s worn out. See pic, also ya gotta hold the blade all the way shut when doing the light test, there is a vacuum pot that holds the blade open a bit without the engine running.

 

Most brake clean these days is just acetone, heptane, and a propellant such as propane.

Can you block the throttle body completely without obstructing the IAC valve?

 

Most brake cleaner now is non-flammable.

 

That is not true.

They are no longer chlorinated and don't make nasty byproducts when they burn, but they definitely burn.

 

I was helping a friend get another friends RV started (carbureted). He had his work truck with him and after we got the wiring fixed on the RV we were looking for starting fluid on his truck and all he had was brake clean.
We tried that for 15 minutes to no avail and then we realized that the can said non-flammable.