p300 misfire detected

i got this code on my 04 aveo. it was a p300 or a p 3000. anyways with my scan tool it comes up as missfire detected. im using the genisys scan tool.
went into the misfire section with engine runnign and showed no missfire.
so i replaced the plugs with ngk platnuims and new wires. new air filter. car still seems to work the same. car only has 30km on it. the only problem that i do notice is when you accelerate then let off the gas then slightly touch the gas the engine stumbles. almost like under load. but still no missfire detected.?
im scratching my head
scott

Have you brought your Aveo to General Motors? Cuz my 2004 Aveo used to have "hiccups" (the RPM went unstable when it reaches 1500-2500RPM) problem on the engine and I already did all the things you did and it didn't make any effect. I asked the dealer to reset the ECU and all the sensors using those genuine scan tool from GM and those problems just dissapeared.

Or check your electrical parts (alternators, battery, cables, etc.)

one thing that comes to my mind that i think was brought up in another post is the exhaust. if there is anything choking the exhaust like say the cat rotted out prematurely and you got bits of metal and junk blockin the pipes then that will cause your car to mess up a bit.

Yeah, problem with the exhaust might a' cause that kind of problem, but don't you think that the possibility is quite small for that kind of thing to happen? Cuz the exhaust system is quite complicated and it's not just one in-lined pipe. You have catalic coverters, flexible pipes, and that huge barrel in the rear that's not free flow, so I think it is quite rare to have problems like a blocked exhaust. Cuz it's hard for anything to block it, seeing that the diameters of the pipes are quite big, and the rear exhaust (under your rear bumper) face downwards (on a standard Aveo).

But it's not a bad idea to take a look on it. Juz my opinion. :wink: