C5 acting strange

[Mystic-1sc]

I have a 2002 Z06 that has developed an issue that seems like a miss, but the car throws no codes other than a P0128 which to my knowledge has to do with coolant temp. I have replaced the plugs and double checked the wires to make sure they are all clicked into place. The car idles fine, but when I go to leave when the car is cold in morning it has a hard time, the rpms try to drop and I have to play with the throttle to bring the rpms back up when trying to get the car to actually move in gear. Its almost like an on off switch, you can get the car going and youll feel it stumble and then pick back up under light accelation. It also has this miss type feeling at cruising speed, but under wide open acceleration it seems to run great. Im just a little stumped because it is throwing no codes, and I hate to just start throwing money at it blind. I've been thinking the o2s could be giving me issues, but Im wanting input from you guys on which direction to go. Car runs great at wide open, but gives me issues at first start in the morning, and then at cruising speed and light acceleration. Any help is much appreciated. This issue has been going on since before the plug swap.

[racingvette]

Cannot really give good answers if people do not state if the car is stock and if not what all the mods are.

This DTC is a PCM test to determine if the tstat is working correctly as if the water temps do not come up in a timeframe expected by the PCM

A stuck open tstat, lower temp one installed and not tuned correctly
starting car with heater on with a lower tstat and/or a higher flowing radiator would take longer to get to operating temp

Also could be like that junk from redline water wetter that is preventing in cold weather the temps to come up as expected.

Assure water temp sensor is reporting and correctly, if so review above and consider testing Tstat.
Keep heater off so less water flow on cold start in colder weather, turn on after temps up to normal

[Jim Lembo]

Need a bit more info from you to try and help out. How many miles on the car? Have you changed the fuel filter? Does the miss go away once the car is up to operating temp? Like Mike asked, do you have any mods?
What did the plugs you replaced look like? Have you cleaned the MAF?

Jimbo

[racingvette]

Jim it might be possible that once the water temp DTC trips is the PCM then does not go into closed loop which would cause rich AFR.

Being OP is not responding to our replies it is impossible to 2nd guess what the real issues are.

Throwing parts in hope of fixing the problem is a waste when a simple use a a OBD scanner would point to the problems in a just few minutes of use.

For all we know the PCM has some crap tune and other DTCs are turned off hiding other problems.

[Mystic-1sc]

The car has a very mild cam, and magnaflow axle back setup. What makes me believe its not tune related is that the car ran great up until a few weeks ago. I made no changes the car it just began to develop a hesitation that got progressively worse which led to the spark plug change that made no difference. Car has 69,000 miles.

[Jim Lembo]

Originally Posted by Mystic-1sc

The car has a very mild cam, and magnaflow axle back setup. What makes me believe its not tune related is that the car ran great up until a few weeks ago. I made no changes the car it just began to develop a hesitation that got progressively worse which led to the spark plug change that made no difference. Car has 69,000 miles.

Saw your post over on CF, so I know you did clean the MAF. If you know the service guy at your local Chevy dealer have him hook up the Tech II to it and scan it, that should pinpoint what is wrong. If not, as a precaution, I would put a new set of GMPP red wires on it,,,,,at 69k miles it's always a good idea to change wires anyway, and I got a feeling that it will solve your problem.

[Mystic-1sc]

Thanks for all the help guys, Im going to try a new set of wires, because honestly why not, and then we shall see what happens.

[FOXBAT]

Golly this sounds very similar to an issue that I experienced while racing.

Check the wiring to the head sensor (driver's side front of the head). While running the engine at idle wiggle the wiring. Does the engine stumble?