Engine Performance problem
2002 BMW X5 V8 All Wheel Drive Automatic 120000 miles
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there is 2 problems actually one is that my car just dose not perform like it used to. what can i do to get the old strength back?
second when i am driving and give the car a couple of kick downs u would feel the gear not changing properly but it dose not happen alot what am i suppose to do?

As to the first question, what have you done so far, what is the history of repairs, has the intake manifold ever been off, has a smooth running test ever been performed, has all the required maintenance been performed? Has the check engine light been on, if so why? At 120K miles you can expect some degradation in the performance.

the intake manifold i opened it once cleaned it and put it back exactly the way it was. as to smooth running test never been done. what i did in its major service i changed the auto leveling suspension,oil for the engine and its filter gear oil and its filter ,oxygen gas sensors thats what i think its called power steering has been fixed. once the check engine light appeared i fixed that problem by putting stp octane something witch fixed the problem in 2 -3 hours of driving its because im from lebanon and the gas is cheated sometimes i hope this information was useful. i have been told headers and to replace the exhaust would bring some power back.. ive put a computer chip that speeds the car could it have effects on the gear shiftings?

I need to know the vehicle identification number please, could you repost at your convenience.