I had an uppipe and downpipe but I put the stock dp back on because I got sick of the smell. Now Ijust have an uppipe.
I got a hold of a factory service manuel and basically the 508 code is a bad ground, bad connection to the ecu or iac solenoid or just a faulty iac.
From what I've read, the iac failing doesn't have much if anything to do with the exhaust system or exhaust mods, more of the thing getting gummed up and sticking, or the solenoid just going out. I read a dozen or so posts from folks on nabisco, cobb forums and here whose went out between 5k and 50k miles, some stock, some not. So I guess we'll see.

 

So the other day when it was like 75 degrees and my car had been sitting in the sun all day I started it up iand dreve it around for a few hours and no problems. The next morning I go to start it up and same thing sh!tty idle and P0508. So this morning I do a little experimant, I get my wifes hair dreyer and warm up the the iac and throttle body for about 5 minutes, cross my fingers and crank it over. No problem, ran fine all morning. This really leads me to believe it's something mechanical in the iac that sticks in the morning when it's cold. When I take it in tomorrow I think the dealership may have a hard time trying to duplicate the symptoms unless I drive it down there cold.

 

So I go to take my car in on thursday morning and it starts up fine and has been running fine the last day or 2. I take it in and the service manager and I agree that it will be extremely hard to diagnose the problem without any symptoms or codes. I drive it all weekend without any problems whatsoever. I run a bunch of errands this morning and it's fine, I get in and start it up to go to work this afternoon and cel P0508 pops up with the same shltty idle (although not as bad as before). Very wierd. I hope I don't have to wait another week to get it in to the dealership.

 

Try cleaning the IAC valve again.....lots of rubbing alcohol and get all the gunk out of it.

 

Think I'll nedd another gasket? It didn't look too dirty the first time but I let a puddle of rubbing alcolhol soke in for a few, agitated it and went in with the Q-Tips and was surprised how much crap there was.

Think it's the iac sticking or a resistance problem? Based on the info in my post. I know I should test the voltage but but I don't have a tester off hand.

TIA

BTW Thanks for the service manuel attachment . It really helped.

 

So I clean it out again, everything seems to work ok, rod does not stick , re install the IAC go to crank it over and celP0508. Now I'm completely baffled. I guess I need to check voltage. Sigh...

 

...well...it sounds like the valve assembly needs to be replaced.....buy a new one and be done with it.
All of your 'tests' have proved that it is, indeed, the problem component and replacing it should resolve the problem.

 

So I took my car to the dealer ship on monday and got it back this afternoon after they replaced my IAC, under warrenty I might add. +1 for the service deparetment.

 

i got same problem here, but my car has 43.000 miles and dealers said its $665.00 to replace that part!
F()CK!!!