Car runs better when cold?
 

I have a 1991 300E,, for some reason when i drive the car cold it seems to have more power and seems to run MUCH smoother.. When its warm it seems to lag more and be a little less aggressive with the power delivery.. any ideas?

When cold the engine runs richer. When warm it operates in "closed loop mode" - the O2 sensor feedback is used to maintain stoichiometric fuel-air ratio. This usually manifests as slight idle roughness, but the engine should respond well to throttle inputs.

Duke

Here's a list of things I would check:

- throttle body bore, make sure it's clean
- egr valve, make sure it closes properly
- injectors could be dirty

cold air is denser than hot air, and denser air carries more oxygen with it.

that's the reason we install cold-air intakes ...

however, cold air also produces more aerodynamic drag ...