My 07 cobalt runs great above idle, plenty of power but at idle it is rough, misses out. Did a tuneup on it, checked all the necessary stuff plugs, fuel pressure, filter, coils, injectors etc. Car sets a code 303, did a compression test and here's the thing, cylinder 2-4= 140# cylinder 1-3= 90# and yet no code 301" only code 303" what's up with that? If this could be a burnt valve or other valve problem I'm not understanding how the car can run so well with no miss whatsoever while driving, can you explain? Thanks for your help.
have the same problem?
Saturday, May 24th, 2014 AT 5:40 PM