IAC valve questions

Reply Subscribe

Thread Tools

Search this Thread

Dec 23, 2013 | 09:14 PM

#21

jagtoes

Senior Member

Joined: Jan 2011

Posts: 1,210

Likes: 14

From: New York

Quote:

Originally Posted by dnarby

Thanks for the link, I'm suspecting I have some sort of vacuum leak now (I also replaced the flame trap and fiddled with the tube going down to the oil separator in the process).

This is a bit strange: Replaced IAC/flame trap/plugs/wires/cap/rotor/air filter, cleaned TB and intake hose (did not mess with the air sensor, don't have the proper cleaner for it yet), checked/repaired every connection/ground that was obvious.

Air flow sensor says BOSCH, it's an '89 N/A.

My brick now idles rock steady at ~700RPM on start up, after driving it for awhile the idle starts to bounce between 200-1000.

At this point, if you rev the engine to 5-6000, it takes an abnormally long time to return to the (bouncing) idle, and it does so by idling down to ~4000, hesitating there, then ~3000, hesitates again, ~2000, etc.

Hopefully this will help solve the original poster's problem as well (not wanting to threadjack).

By the way have you checked the diagnostic box to see if you have any codes. Also at cold start like in the morning you should idle at around 900-1000 RPM until it gets warm. Also if the TPS is not adjusted correctly you'll have a problem at idle. Last is the issue with the throttle adjustment screw. So after you check for vacuum leaks then start with the base idle adjustment with the IAC disconnected. Get a new idle adjustment screw at some auto or hardware shop.

Dec 24, 2013 | 12:52 PM

#22

dnarby

Senior Member

Joined: Jun 2010

Posts: 194

Likes: 3

From: New Haamp-sha

Quote:

Originally Posted by jagtoes

By the way have you checked the diagnostic box to see if you have any codes.

The box quit working when I checked it. Think it's a grounding issues (lots of grounding issues with this car, I already did a bunch).

Quote:

Originally Posted by jagtoes

Also at cold start like in the morning you should idle at around 900-1000 RPM until it gets warm.

It does that OK.

Quote:

Originally Posted by jagtoes

Also if the TPS is not adjusted correctly you'll have a problem at idle. Last is the issue with the throttle adjustment screw. So after you check for vacuum leaks then start with the base idle adjustment with the IAC disconnected. Get a new idle adjustment screw at some auto or hardware shop.

Haven't carefully checked for vacuum leaks yet.

My screw is OK, it's a new IAC, the post originator broke his.

I disconnected the IAC plug just now, and it idled steady at 500. I slowly revved it and it idled down to 1000. Goosing the throttle caused it to go back to 500.

A puzzle, but fortunately it's still drivable, and doesn't rev so high as to slam into gear from park.

Appreciate the help, and Merry Christmas!

Dec 24, 2013 | 12:57 PM

#23

pierce

no mo volvo

Joined: Oct 2010

Posts: 11,289

Likes: 109

From: 37 North on the left coast

ah, THAT sounds like your throttle body is gummed up or sticking, and not closing consistently.

pop it off, and hose it down with a solvent/cleaner while manually working the throttle plate open/close. even get in there with a toothbrush and some WD40 or something, and scrub off any deposits and buildup. then make sure the idle position switch consistently clicks just before its fully closed.

Dec 24, 2013 | 01:09 PM

#24

dnarby

Senior Member

Joined: Jun 2010

Posts: 194

Likes: 3

From: New Haamp-sha

Quote:

Originally Posted by pierce

Thanks, will do. I sprayed some in there but didn't give it special attention. Will see if I can locate a small mirror to look up inside.

Also going to do this Chinese Water Torture (a SeaFoam recipe) - Turbobricks Forums

Quote:

Originally Posted by pierce

then make sure the idle position switch consistently clicks just before its fully closed.

Is there a best method to do that?

PS Merry Christmas!

Last edited by dnarby; Dec 24, 2013 at 01:13 PM.

Dec 24, 2013 | 01:58 PM

#25

pierce

no mo volvo

Joined: Oct 2010

Posts: 11,289

Likes: 109

From: 37 North on the left coast

when you take the throttle body off and have it in your hands, it should be pretty evident that the idle switch is clicking ... for bonus points, clip a digital multimeter in 'continuity beep' mode across the switch, it should beep at idle, and stop beeping as soon as its moved off idle.