Runs rough until warmed up

SOURCE: hesitation , skipping,engine cuts out when accelerating

Bad coil they breakdown when the engine get hot. There is 3 coils total when it starts missing start pulling plu wires until you find the one that is not firing

SOURCE: when cold, it idles rough, revs high then low! After warmed up it runs fine

if it runs high when you first start it then mellows out,, theirs no problem , all of our chevys do that.... but if its sputtering or you hear a quiet popping noise check spark plugs

SOURCE: cold start bog rough idle warms up runs smooth no trouble code

CHECK THE INTAKE MANIFOLD GASKETS FOR VACUUM LEAKS AROUND THE TOP AND UNDER THE PLENUM.

SOURCE: rough idle then stalls

Vacume leak or bad idle motor. With the car in park and running with the hood open listen for leaks moving your hand around the different hoses looking for a change in the sounds that you hear. The idel motor also makes the car idel up to 1500 RPM or so right at start-up then idel down, If it doesn;t the idel motor is likly. Check engine light is on when running? Test for codes, Follow code test charts don't skip any steps!.

Testimonial: "Found the problem vacume leak like you said."

Johnny Brown

• 5763 Answers
• Posted on Nov 28, 2010

SOURCE: 2006 cobalt 2.2 engine, when

You replaced the spar4kplugs but how about the plug boots, these boots are like sparkplug wires and they short out sometimes , with over 100,000 miles i would replace them, also you may have a bad coil . the coil is a complete unit its 4coils in one and may be misfiring, the other problem maybe a dirty throtlebody or bad idle air control valve, you said it runs rough at idle, i would first take it to have the computer scanned to see if there are any stored codes, the computer is always yesting all systems and when it sees a problem it stores a code, this code will tell you what is failing, many autopart stores will scan it at no charge, also if it sees the problem a certain about of times it will turn on the engine light, if you get it scanned and give me the codes i will be able to help you further. for example they may scan it and get a code that reads po302- cyl 2 misfire. this means cylinder 2 is misfiring and then you need to see why its misfiring, it may be due to a plugboot or coil or injector. i would scan it first. hope this helps. good luck.

Testimonial: "i will put boots on. amsoil fuel system cleaner seems to be helping also. thanks for your help"