1995 Cobra

[Mfdiesel77]

I'm having some issues with my cobra to make it California smog compliment. It is from Pennsylvania and it had bbk h-pipe non catted I removed that and installed a factory catted pipe off a 95 gt.
The car ran great before I installed the catted h-pipe not the idle keeps going up and down won't idle normally I installed brand new 02 sensors
Please help

 

[Chythar]

First thing is to check for codes. the computer can store error codes but not light the check engine light. Next - do you have a custom tune on a chip? It's possible the tune is interfering somehow, though I doubt it. Third - are you sure the cats are good on that pipe? None of the cats are plugged up? Fourth - you say you put in new O2's - do you have the old ones still? Would be worth a try to see if things change.

 

[jozsefsz]

Easiest thing to try first is to disconnect the battery, letting it sit for at least 15 minutes, and then re-connecting. This will reset all of the computer's learned fuel trim settings. Putting the proper, catted pipe in place is going to alter the amount of fuel needed at idle, and the computer will need to re-learn its fuel settings. Resetting in this way makes that happen a bit faster. If that doesn't do it, just about any hardware changes can cause a hunting or surging idle. There's a really good checklist frequently posted on this site to address that.