Hello,

I was hoping someone could give me some insight. I am about at my wits end with my truck.

TRUCK: 1999 Toyota Tacoma 3.4L V6 5-Speed
MILES: Almost 270,000

PROBLEM: I have a high idle issue. I will try and be as brief as possible while getting you all the info thus far.

A number of months ago my CEL came on. I had it scanned and it was a P0120 code. I looked it up and it was listing as a defective TPS. Sometimes it would be on and sometimes go off for a few days only to come back on, it was a random deal. At this time the truck would idle usually around 1,000RPMs once warmed up and was very slow to drop RPMs if I say pressed the clutch in at 50mph and started coasting, the RPMs would just slowly fall to around 1,000 to 1,100RPM. At this point it wasn't bothering me, I just didn't like seeing the CEL on.

I started researching around on the internet and found a lot of people with the same code that had replaced the TPS only to continue having the CEL on with the same code. I kept researching and a lot of people were saying to clean the Throttle Body, Idle Air Control Valve, and MAF sensor and that doing that would usually take care of these things.

I didn't have any MAF cleaner but had cleaner for the Throttle Body so I went out and removed the TB from the truck. I thoroughly cleaned the TB on my work bench as well as removed the IACV from the bottom of the TB and cleaned it out. I then re-assembled.

Ever since doing that my problems have been so much worse. First start after cleaning the TB and IACV the idle was sitting at 2,000 to 2,200RPMs when warm. I then did more research and some said to reset the ECU by disconnecting the battery.

After dealing with this for a while and getting more and more annoyed I finally broke down and spent $60.00 on a TPS. I put that on and bought some MAF cleaner at same time and cleaned the MAF. Things seemed to be better now. Truck would idle down to around 750RPMs when warm but would some times want to hang at 1,500RPMs. When it would hang at 1,500 as I came rolling towards a stop with clutch in the RPMs would drop to 750 once usually under 10mph.

I researched AGAIN and the general consensus was to clean the IACV again. So today, I removed the TB again and removed the IACV, gave it a thorough cleaning and re-assembled. Started it up and once it warmed back up to temp it settled to 750RPMs.

Just a bit ago I went to the store, engine was cold at this point. It mostly idled at 1,500RPMs while rolling. Once I stopped the idle settled to 750. If I push clutch in while under say 20mph it falls straight to 750. Anything above that, say I am at 50mph and pull it into neutral and coast to a stop, it will idle at 1,500 until I am almost stopped and then magically drop to 750.

I am at my whits end with this thing!! I love my truck and the 3.4L but its driving me nuts. Anyone have any other ideas?

EDIT: NOTE- Since I replaced the TPS there has been no CEL. Just the idle issue.

 

Have had any time have you lubed the throttle linkage I give mine a spray at every oil change it not more often.

Also look at where the throttle cable comes through the fire wall mine broke the bracket attaching it to the floor.

some ideas

 

After a cleaning the throttle body the throttle plate on mine was sticking against the side of the throttle body and I shimmed it with a washer to center it *but* mine would stay at a high idle even with clutch depressed and was intermittent. I could see where it was sticking and could mimic the stick and stop the high idle manually. Seems the oily gunk I cleaned out of the throttle body had been keeping it from sticking.

Anyway, might check out this excellent thread, with photos:
https://www.yotatech.com/forums/f2/m...-cured-258318/
and see if that gives you any clues as to your situation. Just a possibility...

 

I hadn't lubed the throttle linkage until yesterday, It didn't seem to be sticking but I shot it with a few blasts of some spray lubricant I had. I will check where the cable comes through the firewall as I have not thought to check that out. Thanks for the ideas.

Thank you for the message, I will check into that and see what I find, I will do almost anything at this point to get this fixed. It is so darn annoying.

 

When it's idling high can you reach in and physically close the throttle plate linkage so that it'll drop the idle down? This might indicate that the plate is riding against the bore and is restricting the plate from closing all the way, thus needing to be shimmed with the washer.

 

Thanks for the reply, I tried turning the throttle linkage back but it seems to come back all the way on its on and doesn't seem to be sticking.

I drove the truck yesterday and its still doing the same thing. Once I stop it will idle down below 1,000RPMs but if I am coasting at speed towards a stop sign or light, etc it will idle at 1,500 or so until I am almost stopped and then it will idle down on its on. Seems to if something was sticking it would continue idling high and coming to a stop would have no bearing on the idle dropping but it does so I don't know.

I am pretty frustrated that I can't get it solved.

Also on my throttle body the shaft with the actual linkage where the throttle cable connects is not the same shaft the butterfly plate is on. There is an arm that comes off the main linkage and turns another shaft that the butterfly plate is on, so if I put a washer on there just to try it out it wouldn't keep the butterfly plate from moving.

 

It seems your getting extra air someplace .

Or it is mechanical in nature .

Not getting any more MIL being tripped??

 

I thought about extra un-metered air but I can't find any faulty vacuum lines or anything.

The Check engine light has not been on one single time since I replaced the TPS.

Engine is still doing the high idle. I drive my Honda Civic as much as possible and only drive the truck if I just absolutely have to cause its so annoying. Drove the Tacoma last night and I could leave the clutch out and start braking with trans still in 5th gear. I could slow down to the point the engine was having a hard time in 5th gear at such a low RPM. I then could push the clutch in and the RPMs would go from say 1,200 to 1,800RPM. When I came to a stop it would magically drop to 1,000RPM and sometimes even lower.

I think I am about to replace the IACV. I found one for 60 bucks. Seems like maybe it is hanging or something and then almost at stop it does what it is suppose to. I really don't know. I have cleaned the IACV now 2 times, maybe 3.

 

I had a high idle after cleaning my IACV, couldn't fix it for the life of me, so I bought a new replacement from eBay for around $60, looked identical to the OEM and has been running great ever since.

 

Thanks for the response BlazeRunner. I think that is what I am going to do, I found a new replacement IACV on Ebay as well and its just under $60.00 with Free Shipping. I hate to spend that money and then it NOT fix it but I don't know what else to do.

Just seems to me the IACV could be to blame because like I said it will idle high until I am almost stopped and then it drops, its almost like right when I come to a stop the valve unsticks or something.

I drove the Tacoma yesterday and it was doing the high idle, about 2 miles form the house when I pushed clutch in to coast at 2 different intersections the idle dropped right to 750 just like it should.

So that tells me the IACV is acting up sometimes, other times it works as it should.