[Paradox001]

Well, I've searched around the forums here and other places on the web for things to try with no luck so far! Stumped

I have a 1998 Tacoma 3.4L with about 99k miles. It started throwing a check engine light with code P0505 which means idle control system malfunction. Then, it started to idle too high (1800-2000rpm).

What I did:

Cleaned Throttle body
Cleaned IAC valve and replaced gaskets
Checked IAC valve operation and resistance according to repair manual
Checked throttle position sensor resistance
Throttle valve is in fully closed position when it is idling
Looked around for dry/leaky air hoses
After doing all this it worked fine for a day...... Then started right back with idling high, however it has NOT thrown a P0505 code since doing these things.

Anyone have any ideas??

 

[karazy]

Have a look here http://www.tankota.net/repair/Repair_Manual/03tacoma/di/eg5vzfe/cip0505w.pdf

 

[TcmaBoy]

Have you checked for vac leaks?

Is the throttle opener working properly?

 

[Paradox001]

The throttle is definitely fully closed at idle and it is still ~1900 rpm. I'm thinking it has to be the IAC valve either stuck open (it was working fine when I tested and cleaned it) or the computer is telling it to stay open for some reason

 

[goran_volvo]

Plug the air hose which goes into IAC valve, check if the idle goes down, and, there you go

 

[Paradox001]

Ok, found the problem. There were no leaks anywhere, but unplugging the power to the IAC valve (so that it closes on its own) brought the throttle right down. So it was the IAC valve staying open that was causing the high idle.

I checked the leads from the ECU to the IAC, they were good and so was the signal. So I replaced the IAC valve and it works great now!!

Got it cheap on EBay luckily, since it is a $250 part...

 

[de.florez]

Alright so I don't know a whole lot about cars but my 97 toyota is doing the exact same thing. I know that the IAC is out of spec, and I don't want to spend the $450 the shop wants to replace it. It sounds like I can clean it without replacing it, but I dont know howe how to get to it. Any direction anybody can point me in would be great.