I just changed my '06 525I for a '06 550 I with just 35,000 miles. The only issue i find with the car is that with the A/C off RPM is around 500 when i turn on A/C they increase to about 700 to 750 RPM is this normal on the 550

 

Perfectly normal, mine does the same thing. I believe its just the compressor engaging.

 

yup, normal. the rpms go up with the ac on, because of the extra load the ac compressor puts on the engine.

 

Thanks for the input. Love the car hate the gas mileage compared to the 525i