Hi. I just purchased a used 2008 Mini Cooper Base, automatic transmission with 52k miles. Car is suffering from hesitation at low rpm and or take off and only getting 30.5 mpg on highway. My previous 2008 Base was getting 36.5 mpg on highway.

I have tried the following:
1) Replaced spark plugs.
2) Replaced one spark plug coil boot (#3) - hard and cracked while removing.
3) Did 2 seafoam treatments through PCV valve hose.
4) I have removed and cleaned the exhaust manifold/intake valves (seafoam and brushes) - not much carbon buildup.
5) Removed valve cover and replaced gaskets as it was leaking (gaskets hard). Removed yellow diaphram from valve cover and cleaned - not much buildup. Also soaked valve cover PCV valve maze in seafoam - not alot of residue and blew out with compressed air.
6) Added Techron cleaner to fuel tank.
7) Replaced air filter.

No change. Still have hesitation and same low gas mileage on highway. I don't know what else to try as I don't want to keep chasing the problem with parts.

Idle is fine. Does not run rough. No check engine warnings. Does not use a lot of oil.

Replace valve cover? O2 sensors?

Please HELP! Thanks.

 

Have you had to replace the timing chain yet? Do you hear any "knocking" from the passenger side of the engine? I just had to replace my timing chain and had stuttering and power issues at low RPM's. There is a chance that if the timing chain has problems, your MPG could suffer. This is purely speculative.

 

Thanks for the reply tylewis. I believe the timing chain has not been replaced yet and I do not hear any knocking noise from the passenger side. When I had the valve cover off, I didn't notice anything odd. Very frustrating.