Idle around 1,300 How can I get lower?

porsche4life · porsche4life's Garage

I changed out the throttle body to one that had had the chamber polished and bored. Now the idle is high even with the screw all the way in. What can I do?

choinga · 07-03-2009, 01:56 PM

well, clearly there's something wrong with that TB. If you switch back to stock and it works - then you know what the problem is.

Techno Duck · Techno Duck's Garage

Make sure the TPS is adjusted correctly on the throttle body. It should click when the throttle plate shuts completley.

Also you have to disable the ISV when you reset the idle speed using the bypass screw on the throttle body. Check ClarksGarage for a good explanation on how to do it.

porsche4life · porsche4life's Garage

I saw that on clarks. Where is the diag plug it mentions?

Techno Duck · Techno Duck's Garage

Inbetween the firewall and the drivers side strut tower. It has a black plastic cover... its sorta under the fuel vapor purge stuff.

Slam · 07-06-2009, 10:28 AM

Are you sure there are no vac leaks?

porsche4life · porsche4life's Garage

I am fairly certain there are no vac leaks. I mean it idled fine before I changed the throttle body

Slam · 07-06-2009, 01:50 PM

Sucking air around the screw? It's amazing how little air makes a difference.

krystar · 07-06-2009, 01:52 PM

still sounds like a vac leak. take a cig lighter and push the button to let only fuel out w/o lighting it. point at some seals and see if engine noise changes

porsche4life · porsche4life's Garage

Hmm I'll look into that. Can I change the cac lines without taking the manifold off? I have a new vac line kit from Lindsey in my toolbox I was just waiting for a chance to change them

SuperXRAY · 07-06-2009, 05:16 PM

Ditto on checking TPS. However, I would also suggest that your throttle plate isn't actually closing to spec. If the TB has been polished, then material HAS BEEN REMOVED from the body itself, thereby making the hole bigger. TB's are actually set on a flow bench, but you can get it close just by backing the stop screw (the one that stops the throttle plate, near the spring on the throttle cam) until the plate doesn't move any more. Then screw the stop in 1/8-1/4 turn. Then set your TPS accordingly.

I suggest checking the TPS and throttle plate before making any adjustments, otherwise you will be chasing a wild goose. As stated numerous times in the service manuals, one can only adjust the idle on a properly running engine...that means that all the vacuum lines work, the TB is set correctly, the AFM works, etc...

porsche4life · porsche4life's Garage

Checked the vac lines with a lighter and nothing. Going out in a minute to put the old TB back on.

porsche4life · porsche4life's Garage

Ok I put the old TB back on and it runs fine. Ran most of the vaccum lines new while I was in there. Haven't gotten to drive it b/c I have an injector dripping(having one overnighted).