X5 sluggish and low MPG
 

After an extensive service (valve cover, valley pan and intake manifold gaskets, spark plugs, coolant hoses, PS hose, 02 after cat sensor, air boot, thrust arms, radiator, etc.) my car now occasionally throws me a p0170 code and generally feels sluggish and dull. I have an average 8 MPG, without flooring it, but what gets on my nerves is that it does not accelerate as it should, especially after kick downs. I have 93k miles on it.
I must add that i've added the pre Vanos intake and a Flowmaster setup.

Any help would be much appreciated.

Regards,

Sam

I would do some searching on BMW forums for P0170. Lots of info.

I already did. Most likely MAF and/or pre-cat O2 sensor. its the low MPG that troubles in combination with the poor acceleration. i don't see the connection

Normally the signal from the pre-cat O2 sensor(s) tell the computer how to adjust the fuel mixture. Therefore if the O2 sensor is bad it could be making the computer add more fuel than is needed, causing poor mileage and poor performance.

Replace pre-cat O2 sensors ^^
Clean the MAF sensor with CRC MAF Sensor Cleaner.
Make sure tire pressures are correct.
Clean your throttle body
Also make sure your water/coolant temperature sensor is plugged in!

Question: did it only exhibit this behavior after the extensive service?

If MAF is not working that for sure affects to performance, and probably to MPG also.
I had broken MAF in my 530d and it was very slow, it felt more like 1.6L engine instead of 3.0 turbo diesel :).

If you suspect the MAF you can perform a quick and dirty test by unplugging it and see how it performs. If performance returns the MAF likely is the culprit.

As for cleaning the MAF it doesn't hurt but I'm not a fan of doing so because, IMO, it rarely helps.

CPS (Camshaft Position Sensors) could be on it's way out as well...

I replaced the MAF with a new one and guess what, problem solved! Its a good thing i stock spare parts. Thank you all for your replies!