Hi guys,

I hope you can help me with this one. I have a TOYOTA Prado with a 3.4l 5VZ FE engine. The truck has 100.000 miles on it and about 6 months ago it started reving up quite high during cold starts. Most of the time the CE light would come on with code 33 (IAC).
Since then I replaced the IAC, the CE light doesn’t come on anymore however the idle speed is still high when the engine is cold (about 1800 RPM) and when it's hot (about 1050 RPM).
I have also replaced the cold start temperature sensor, cleaned the MAF, cleaned the TB and checked for vacuum leaks.
The weird thing is that there is a condition where the idle speed is right. That is when the engine gets completely warmed up and I turn it off for a couple of minutes, then when I start it back up again it revs nicely at 750 RPM. If I then start driving it will never come back down to that level.
Another weird thing I noticed (after changing the IAC) is that when the truck is moving while in neutral the idle speed is slightly higher than when the truck comes to a complete stop. It's like the ECU determines that the truck is moving and "orders" a slightly higher idle speed. I did not have this effect with my old IAC valve ……
I am now totally confused since I think I have no place else to look for a "cure". I hope you could advise.

Cheers

 

so..... I guess there is no hope

 

My high idle was cured by a good throttle body clean (complete pull-off), but looks like you've already tried that...

 

I was going to suggest cleaning the IAC, but you put in a whole new one...

 

Any guess about this one ???? Thank you ....

 

I have a 2000 3.4 in a Tacoma and mine does the same thing. I get no codes I just thought it was normal.

Mine only does it with the engine cold after reaching operating temp it idles fine

 

My problem started that way but then it got worst and after a while the idle speed remained high also when hot

 

My high idle was cured with cleaning the IAC... since you already replaced that, I would say you should look for a vacuum leak... particularly between the airbox and the throttle body.

 

It could possibly be the TPS connected to the TB. I had an old Acura (Honda) Vigor that had one go bad where the contact points inside the TPS did not relay the correct information to the ECT and would buck under throttle. You could check the voltage signal if you had a service manual for the Prado. Since you are driving a Prado (country?), I would guess it is similar in set up to our 4Runner but who knows.

..... X2 or X3 on the vacuum leak. Check every hose, including all around the intake, twice.

 

Not trying to be a jerk but you said the coolant sensor was replaced. Are you sure it was the sensor and not the sender that controls the dash temp gauge?

Another guess, is the power steering oil pressure switch. It could also affect idle speeds. I have never heard of anyone having a problem with this on a 4runner though.

 

I will recheck the hoses but I am pretty sure that they are OK. If I had an air leak then I would have a high idle under all circumstances. However, there is a case (as I described above) where the idle is fine whch rules out (I guess) any "mechanical" failure.

Yes it was the sensor. I am pretty sure about it ..... The power steering pressure could be a reason but I do not know how to check it .....

 

I really believe that the solution to the problem lies behind understanding this strange case where once the engine gets hot and is turned off for while, if its then restarted it idles just fine at around 750 RPM….. What can be the reason that could cause this ?
If I then start driving and i.e. come to a stop, the idle never goes down below 1050 RPM …

 

Try cleaning your dashpot... Maybe its gunked up and when it gets hot enough it relaxes but it still could be stiff.

 

Thanks for the tip mate but the problem was found to be a blown head gasket. Unfortunatelly, along with the blown gasket I found a crack in the head

 

so, ive used the search button and stumbled across this thread. here is my problem with the idle. recently ive dont a bit of work on my engine. it was throwing code p0304, misfire cyl. 4, and since i didnt know what kind of maintenance the previous owners did or didnt do, since i was lied to when i purchased the truck off island, i started with the basics. changed the spark plugs. checked my sparkplug wires, noticed one of them was bad (cyl. 2, go figure), checked the coils, all g. since i had all of that checked off, i narrowed it down to the injector. so apart comes the plenum and what not. at the same time i cleaned my intake filter since it was full of gunk from the prev. owners. since i was taking all of that off, i decided to change my valve cover gaskets too. irrelevant to the high idle problem though...haha. well, when the plenum was off, i noticed that there was a lot of bunky build up on the throttle body butterfly. i ended up bombing that with carb cleaner and brushing it with a soft bristle brush. got most of the gunk off. at the same time i did that, i noticed some of the carb cleaner coming out of the IAC. didnt think much of it at the time, but im wondering if that "cleaning" from just having the liquid drain through would cause the idle problem im having. before at start up, it would idle around 1500 and then drop back down to below 1000. now, its the opposite. cold the truck idles around 1000 and when the engine warms up its anywhere from 1500-1800, not on the throttle. could it be something as simple as an overtightened throttle cable?