Runs better when cold

[froggiegit]

Hi, Bought a 2001 (W203) C200K estate 2 years ago and very pleased with it. Recently it runs great from cold but seems a bit more hesitant when up to temperature. Had some codes came up from time to time - before and after the problem. Cleaned the MAF sensor with contact cleaner and the switch/air tubes leadin from/to it also the cam sensor and air sensor switches. No longer get the codes. Also car doesn't always kick down from 3rd to second so had the transmission fluid and filter changed. Still get the problem. It's only intermittent, sometimes it runs perfectly other times its a pain.Could this be fuel filter related as when cold it ir perfect (maybe due to the richer mixture). Plugs have done about 20K miles - Mercedes recommend change at 50K ish.
Any advice much appreciated

 

[grober]

Might be worth changing the thermostat if its engine temperature related?

 

[froggiegit]

Might be worth a try but it gets up to temperature normally and stays just above 80 deg all the time. (has done since I've had it)

 

[grober]

Could be running lean if there is an air leak somewhere after the MAF sensor. Have you had a look at the plugs [ say after a long run up to temperature to see if there's any sign they are running weak?

 

[froggiegit]

Thanks, good idea, might have a look tomorrow
Robin