Please diagnose, high idle when car warms up

[thewraith]

My car idles fine when cool. Once the car warms up it starts to idle high, the idle doesn't jump- it just stays high. I have changed the ic pipes to hard pipes, put a new air intake in, new thermostat, and have a IAC sensor on the way. However- my idle is not jumpy, it just goes to about 1.5k rpms once the car reaches normal operating temperature and stays there. This is very annoying with the 3" exhaust and dp on the car.

Thanks in advance for any advice.

 

[jshuman]

I had a similar problem with the idle being normal when warming up, but then climbing to 1500 when warm. There is a really good idle diagnosis guide on vfaq that I used. The BISS ended up being my problem. The o -ring had went bad and allowed the BISS screw to back out a little bit, but it was just enough to raise the idle up to 1500. First, I would do a boost leak test since you just put new IC pipes on. Also you might want to check to make sure your throttle body is not sticking. I do not think it is your IAC beasue it doesn't sound like you are having surge issues. Of course it wouldnt hurt to swap it out just to be sure. I hope that helps.

 

[LambdaJoker]

http://www.vfaq.com/mods/BISS-1G.html

http://www.dsmtuners.com/forums/showthread.php?t=191137

 

[thewraith]

Thanks a lot! I will try these today and get back to you on it.

 

[thewraith]

One more question if i may. In the vfaq for a 2g, it states that I have to use a $1800 scan tool to do the BISS adjustment- is this really necessary? Please advise.

thanks again
meek

 

[jshuman]

I have dsmlink so I can adjust the biss while loggging iscposition. Before i knew that though, I just adjusted the biss until the idle was back where it was supposed to be (750rpm for you). If your biss has been backing out, it will force your isc to try to work outside of its range. Eventually it will back out to the point when the isc cannot keep the rps steady and it will begin to surge. Assuming that your isc was set correctly to begin with, you should be able to simply turn the biss until your idle is at the right rpm and your isc will once again be funtionig in its normal range. Of course this is only if your biss screw is your problem. Unless your biss o-ring is worn out, I doubt this is the cause of the high idle. My understanding is that the biss is the last thing to be adjusted. If you adjust the biss and the high idle comes back, you know the biss screw was not the problem.

 

[thewraith]

ok, i will go and get a #5 o ring today and replace it. i guess to replace it i just take the old biss screw out w/the car off- put the ring in and then adjust the biss till everything sounds ok?

 

[jshuman]

Yeah you might count the number of turns out so you can screw it back in to the same position. That way you dont force the isc to go even further out of its range.