high idle, stumped.

GHOSTOWLGRID · December 14, 2015, 12:41:36 AM

90 tgp.
3.1 v6 turbo.
4t60 trans.

The car has a high idle right away after starting it.
I checked every vacuum line and evenremoved the top intake to check the plastic hoses.

The IAC seems to be opening up and not closing.
I replaced the IAC with a known good one and the same thing happens.

So I manually set it by hand for a good idle and left it unpluged
No SES light or codes.
EGR tested fine and is not pluged or sticking open

Cleaned throttle body, tested with turbo pipe to throttle removed, no boost at all.

I am kinda lost. What could possibly make this happen?
All thats really left to swap out is the IAT and TPS, and I do not have spares of those.

Heartbeat1991 · December 16, 2015, 07:53:05 PM

I had one doing this recently. Believe it or not, mine was the ECM. For a while I just left the IAC unplugged.

GHOSTOWLGRID · December 17, 2015, 09:13:30 AM

Quote from: Heartbeat1991 on December 16, 2015, 07:53:05 PM
I had one doing this recently. Believe it or not, mine was the ECM. For a while I just left the IAC unplugged.

I thought the same thing so I swapped the ECM and eprom both with known good from another car. No difference.

It works okay with the IAC unpluged and set to 1K idle, however it would idle better if it was computer controlled, especially when I run the air conditioning and stuff that drags the engine down.

killinprixs · December 18, 2015, 02:34:22 PM

power steering pressure sensor bad thinking theres a load on the engine?

GHOSTOWLGRID · December 18, 2015, 05:27:51 PM

I checked it and its fine.

I am probably going to change the TPS and see what happens, nothing else really controlls the IAC and its only 20 dollars new. I hope this fixes it, I'll reply if it does or not.

GHOSTOWLGRID · December 19, 2015, 07:39:40 PM

Update:
I replaced MAP, TPS, IAC and now its revving to 3K rpm instead of 2K rpm.
The IAC counts now go to zero and the idle is high.

However when I fully extend the IAC manually and unplug it, the engine will idle at 800 rpm according to the book. And it does.
I am stumped.

killinprixs · December 20, 2015, 08:56:29 PM

-when you unplug the IAC , what are you getting for vacuum ( assuming you have an accurate vacuum gauge)
- Is the PCV good?
- Does idle increase when you remove oil cap running
- Did you unhook the battery and let the car properly relearn?
- have you tried spraying throttle body cleaner around the intake to locate possible vacuum leak.
- transmission vacuum modulator leaking or sucking in transmission fluid?

GHOSTOWLGRID · December 23, 2015, 06:34:59 PM

Thanks for the help on directing me what to check.
The IAC would open but not close.
1 wire in the plug was intermittently broken in the plug eventually it pulled out and I found it.

Idle if fine again.