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I have a surging problem when holding at a constant speed and or RPM, also on deceleration. feels like the car is bucking. stange part is there is plenty of power when accelerating. Have had this to 2 shops + GM tech , and no results.
dropped off car today to vette specialists, say it's most likely not fuel related, because it surges on deceleration, you said the same thing he did about a possible clogged cat. hope thats it.
have you done any ECM/PCM reprogramming? What grade of fuel are you running? I Also check your fuel injectors.. I injector stuck shut would cause cyl. to run lean.. and surge.. DANGER DANGER DANGER! Also, Check for operation of the O2 sensors.. if you have a scanner log some data and we'll check it out for you.. if not but a voltmeter on the 02 wire while the engine is idling (warm idle in closed loop) and the readins should vary pretty rapidly.. between 100mv-800mv 450-500mv is perfect stoich..less is lean more is rich.. however you must look at the net avg. of the swing - not just instintanious readings. could also be a fuel pump or clogged fuel filter.. malfunctioning MAP, IAC or evaporator purge system.. could also be bad spark plug, wire or coil.. theres a lot to look for.. start eliminating possiblitues..
Maybe you could run your " R-12 purge tubes" in front of the windshield. Give the stop light competition a little "spray" like the big straps with NOX. :D