Very High Idle! 2100rpm

[sloracer92]

Hey Guys,

I really need your help on this one....sadly, this is my first post (not the first post I wanted! ). I spent about an hour searching through the various Boxster forums but couldn't find anything similar to the problem I'm having.

I have a 1998 Boxster w/ ~137,000 miles. Manual Transmission.

I spent a few hours today replacing my trans/diff oil and then diagnosing the intermittent P0410/P1411 CEL that I've had since purchasing the car. In diagnosing the CEL, I followed the steps that Loren posted about diagnosing Secondary Air Injection problems. After using Durametric to activate the air injection pump (and confirmed that it is, in fact, working), I started the engine and disconnected the vacuum line connecting to the air change over valve to check for the presence of vacuum (there was). In starting the engine to check for vacuum, the engine idle inexplicably went to 2100rpm (not fluctuating). Even after reconnecting the vacuum line to the change over valve, the idle remains at 2100rpm. I've checked the throttle cable to make sure that it isn't hung up on anything (it isn't) and I unplugged the battery to reset to DME (just in case). Even after restarting the car 4 times now, the idle issue remains. When I was activating the air pump using Durametric, I accidentally clicked on "Start" for IACV and then clicked on "Stop" even though no noise was made. Could that have been part of the problem? I'm at a loss!

Any help would be much appreciated!

Chris

[JAAY]

This is a long shot but it has happened to me. Check the throttle cable right behind the drivers side rear tire. There is a little black box where it connects and it can get knocked out of alignment while working on the car. The cable may not be seated correctly in there. That has been my source of this issue once or twice. Please update us on what the outcome is.

[sloracer92]

Thanks for the quick response JAAY. I went down to the garage to double check the throttle cable and it appears to me that the cable is seated correctly. I am convinced that it must be some sort of vacuum problem now, but I can't imagine what me removing and replacing the vacuum tube to the change over valve would have changed!

[ppbon]

... more air is coming through the throttle body.
You either have an air leak in one of the rubber connectors or the idle control valve is dirty and stuck open.
Happy Boxstering
Pedro

Originally Posted by sloracer92

Thanks for the quick response JAAY. I went down to the garage to double check the throttle cable and it appears to me that the cable is seated correctly. I am convinced that it must be some sort of vacuum problem now, but I can't imagine what me removing and replacing the vacuum tube to the change over valve would have changed!

[sloracer92]

Thanks Pedro! You were spot-on. I removed the idle air control valve and it was caked with carbon build-up. Replaced it once clean and the idle speed is back to normal.

[AndyA6]

I say it again and again, this forum is so good!