I've just replaced the fuel pump and relay on my 540. The car starts up fine and seems to drive when its cold okay. Then when it warms up it runs terrible to the point where it is floored and it is barely moving. It just gets worse and worse as you drive it. When you accerlerate it surges a lot and barely gets up and going. Anybody had experience with this or have an idea?

I did some research and for it to run this bad it would probably be a MAF or reference sensor. At the same time it could be a Coolant temp sensor, but apparently they would not cause the car to run this bad. No black smoke eithier.

if its a higher mileage car n depending what maintence you have done on her far as tune up goes.i thinks its your cat are bad . the car runs worse as it warms up likes its choking itself is a sure sign of cats . i would disconnect them and run it n see if it clears up .just a thought

If cats are clogged they are clogged, no matter the temp. I would think its a sensor but with no engines codes I'm stuck with my thumbs up my..

Luckily my dad is outta town with his 740i sitting up at his house. Maybe I'll yank the MAF to test and to see if thats it. Anybody think eithier the cam or crank position sensor is going ?

sorry dude the car can sit at idle n run all day its when you give it gas it fall on its ass. its a suggestion not a fix . as the car warms up n you have no power is a sure sign that the cat may be bad

Any check engine lights? Most of those parts don't fail without throwing a code.

No check engine or codes from the scanner.

If your MAF goes out the engine will not run. Try disconnecting it and then starting the engine, the car should not start.

After digging around and messing with stuff I changed the plugs out, and it fixed it! I have never experienced bad plugs to act like this before.

If your MAF goes out the engine will not run. Try disconnecting it and then starting the engine, the car should not start.

Actually it will. You can do this to test if your MAF is functioning properly.