Runs fine but


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Oct 6, 2003
Hi..My car is starting to pi#@ me off....Runs great when it is cold but after it warms up and goes into closed loop it runs like total sh#t...Checked and replace MAF, checked engine grounds....It sounds like a pro-stocker after it warms up and is idling....Choppy rough idle, and it has popped through the intake when giving it part throttle.... Runs great at WOT pulls hard but doesn't run right after it goes into closed loop... It has a slight miss to it at about 2,000 RPM too....Anything above that is goes away....Must be a sensor somewhere???? I've also replaced ignition module, and coil pack too.....

Thanks in advance......
I would check the cam sensor. Not the electronic part, but the shaft play up and down. Also the back lash. These cars are getting pretty old, and I have started seeing more mechanical failures in areas that used to be mostly electronics. Later....Danny
It almost sounds like O2 sensor. ECM ignores the O2 at WOT and in open loop. Once you go into closed loop, the O2 comes into play. Maybe you already swapped this but it's the only thing I can think of other than perhaps swapping ECMs or checking that the chip is properly seated and the pins on it are making contact.

Popping through the intake is definitely lean. Popping through exhaust would be rich.
My 02 is about 1 mo. old (AC-DELCO), and according to my scanmaster it seems normal with the numbers jumping all around like normal.....My cam sensor is brand new when I rebuilt the engine....About 5,000 miles ago....I did a WOT run and the scanmaster said the 02mv were at 850, with about 2* of KR.....

Is there any other sensor that will cause it to do this when it goes into closed loop?????:confused:

And by the way I am currently using my stock chip for right now....
Are you getting any funky water temp readings?If the coolant temp sensor is bad,or if you got a bad connection at the cts it will tell the ecm that the engine is still cold and then it will richen up the a/f mixture and load up on you.Check to see if your sparkplugs are wet from running rich.If that's not the problem get rid of the stock chip. .Also if you have a 160* thermostart with the stock chip it may not run good.