High Idle - Can't seem to solve it

paradox001 · #1 (**permalink**) 02-15-2008, 01:38 PM

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??

The Phoenix · #2 (**permalink**) 02-15-2008, 10:22 PM

I wonder if it has something to do with the initial startup for high idle that warms the catalytic converters. You checked alot of the main culprits though. I'm stumped.

paradox001 · #3 (**permalink**) 02-17-2008, 07:15 PM

Yep, not sure what is going on. Also checked the PCV valve and cleaned the MAF sensor.

Since it worked fine for a day after I cleaned the IAC valve, i'm tempted to open it back up and see if that valve is stuck open now or something

The Phoenix · #4 (**permalink**) 02-18-2008, 04:31 PM

The IAC can act up. I would replace it as it's not that expensive.

paradox001 · #5 (**permalink**) 02-19-2008, 12:06 PM

It worked fine when I tested it but I'll have to take off the throttle body again and test the valve another time. I'd still like to avoid a $220 part replacement if possible

HOGWILD · #6 (**permalink**) 02-19-2008, 04:41 PM

Have ya ever changed PCV or checked the hoses for leaks or loose as in popped off?

paradox001 · #7 (**permalink**) 02-26-2008, 12:33 PM

Ok, it was the IAC valve. Weird since it had worked fine when I cleaned and tested it, but unplugging the power to it brought the idle right down.

So I replaced it with an ebay used one and it works great now!