Cascade Crew

aaron_sK · Posted: Tue Jun 13, 2006 6:53 pm Post subject: Low rough idle... IAC?

For about a month my car has been idling like crap, and getting slowly but progressivly worse. My usual idle is dead on 750. However recently my tach has been jumping between 500 and 740 at idle, and the engine is bucking a bit, and running like sh**. It also smells like it's way too rich.

As soon as I rev it up past 1500-2K it runs great, and has plenty of power. It never gets close to stalling or anything. The problem is most apparent after the ECU hits closed loop, but before the car is fully hot. Once it's been running for about 15-20 minutes, it evens out a bit, but still has a noticable stumble at idle.

I'm pretty sure it's not a cylinder problem, as the stumbling is random, not consistent. O2 sensor is brand new, so are the cap, rotor, and plugs. Wires are in good shape. No codes at all. I was thinking IAC sticking closed, or maybe an EGR problem. Any ideas before I start randomly digging around in the TB?

BigDaddyVu · Posted: Tue Jun 13, 2006 9:31 pm Post subject:

I had that very same problem cured that with a new iac (the usually fail beings its a stepper motor)

aaron_sK · Posted: Tue Jun 13, 2006 9:46 pm Post subject:

Is there a way to test it, or should I just buy another one outright?

Al Hasse · Posted: Tue Jun 13, 2006 9:58 pm Post subject:

Looking over on TGO, Trickster has a reply to a post asking the same thing. He posted a page with a test procedure.

http://www.thirdgen.org/techboard/2233401-post2.html

aaron_sK · Posted: Tue Jun 13, 2006 10:10 pm Post subject:

Cool. Thanks man. I've got to swing by Schucks anyway. I think I'll check and see if they sell a tester.

aaron_sK · Posted: Wed Jun 14, 2006 1:06 pm Post subject:

Hmm.... don't know if itm akes a difference, but today it was idling on the high side, somewhere around 850-900 RPM's. Still idling like crap.

BigDaddyVu · Posted: Wed Jun 14, 2006 5:53 pm Post subject:

just buy a new one there cheap the heat really kills remember to set and adjust the iac valve before install or you'll bottom it out and strip the stepper motor out.

aaron_sK · Posted: Wed Jun 14, 2006 5:56 pm Post subject:

Schucks has them for around $40 on their site. That's cheaper than I expected. Tomorrow I'll have to run down there.

iansane · Posted: Wed Jun 14, 2006 10:52 pm Post subject:

They're $49.99 I think. I bought one before I started working at schmucks because I busted off the backside of my IAC.

Twilightoptics · Posted: Thu Jun 15, 2006 10:08 am Post subject:

Check the basics.... plugs, timing, cap, rotor, etc... then maybe yank the throttle body off and clean it and the iac passage.

aaron_sK · Posted: Thu Jun 15, 2006 12:21 pm Post subject:

Way ahead of you on that, Paul. All are brand new, and I checked them. Pulled the TB off today. It's shot. The IAC valve was siezed, and I snapped it off in the TB while trying to remove it.

I pulled the bottom off, and those screws where pretty much shot too. The entire IAC passage and plunger were coated in some sort of carbon crud. Doesn't really matter now, I need at least the bottom half of the TB, if not an entire one.

iansane · Posted: Thu Jun 15, 2006 4:55 pm Post subject:

How many of the screws did you bugger up? On my 87 when I did the TB bypass I pulled te TB off and cut away allta extra material so only the IAC and passage was left. Could that work?

aaron_sK · Posted: Thu Jun 15, 2006 5:19 pm Post subject:

Actually, I cleaned the screws, and flushed out the blind holes in the upper TB, and it's not as bad as I had first thought. And since I'm going the coolant bypass at the same time, the only thing I really need to seal up is the IAC port.