C5 2.0i (not Hpi) 16v Auto Misfire

[mlkey]

Hello,

 

I purchased the above a few days ago, and am noticing a slight, irregular yet frequent misfire. It predominantly occurs within a few minutes of a cold start. I changed the spark plugs yesterday and perhaps it has improved very slightly. I can not notice the misfire when the engine is idling, nor can I detect it if I raise the revs. It only seems to be detectable when the car is moving under very light throttle loads, and when in 3rd or 4th gear, when the torque convertor is locked.

 

It is a lovely car, 2004 model with just 30,000 miles covered, I really would like to get to the bottom of this. Does anyone have any ideas where to look next? I had it scanned for codes, there are none stored.

[mlkey]

Anyone?

 

Hello,

 

I purchased the above a few days ago, and am noticing a slight, irregular yet frequent misfire. It predominantly occurs within a few minutes of a cold start. I changed the spark plugs yesterday and perhaps it has improved very slightly. I can not notice the misfire when the engine is idling, nor can I detect it if I raise the revs. It only seems to be detectable when the car is moving under very light throttle loads, and when in 3rd or 4th gear, when the torque convertor is locked.

 

It is a lovely car, 2004 model with just 30,000 miles covered, I really would like to get to the bottom of this. Does anyone have any ideas where to look next? I had it scanned for codes, there are none stored.

[seefive]

Anyone?

 

 

I had this problem on a 2002 petrol manual

It would misfire as it was warmong up, ran fine stone cold or warm

Diagnosis was sticking valves/lifters

 

Wynns lifter cleaner helped, but I never had it fixed - too expensive.

 

Changed the car 2 years ago (for another C5 petrol auto mk 2,no such problems with the new car)

[mlkey]

I had this problem on a 2002 petrol manual

It would misfire as it was warmong up, ran fine stone cold or warm

Diagnosis was sticking valves/lifters

 

Wynns lifter cleaner helped, but I never had it fixed - too expensive.

 

Changed the car 2 years ago (for another C5 petrol auto mk 2,no such problems with the new car)

 

Thanks seefive, my symptoms are exactly the same. Fine on cold start, fine when up to temperature, but during the warm up I can feel it kicking. I will try the Wynns and an oil change.

[seefive]

Thanks seefive, my symptoms are exactly the same. Fine on cold start, fine when up to temperature, but during the warm up I can feel it kicking. I will try the Wynns and an oil change.

 

 

Another possibility is the air pump. If you look at the passenger side of the engine bay, front, you will see a small pump, about the size of a hair dryer fan. This should kick in while the engine is warming up, to keep the mixture from getting too rich. You can tell when it's working by feeling it, also listening.