Issue with RPM hanging after rev.

[justanothrone]

This is another member on the forum. He has a 2011 6 speed 135i with currently about 17k miles. Oils was just changed at 13k miles in Oct 2013. Within the past two months the car isn't feeling right I was told.

Issue:
1. When reving the car, the throttle feels like slower to start. To clarify, before it would start to rev with a slight touch of the pedal, now it requires requires a deeper push to begin reving. Once the car starts to rev, letting off the throttle doesn't drop the rev immediately like it used too. It would hang there for a few seconds and then begin to come back down.

2. Concurrently the recirculating valve started to sound different, instead of making a PSSSH when purging, now it makes a higher pitch laser like noise like PEW.

He has brought the car to two different BMW dealership here in MI since it is still under warranty. Both diagnose and said it just fine and dandy. It obviously isn't fine because we compared his car to two other 135i in the area, and out rev drops as soon as we let off the throttle.

Trying to help the guy out, if anyone has an more questions, ideas or leads on how to correct this issue feel free to comment.

[darkrom]

Could be a boost leak, but it sounds like its slow to rev from a stop? If that is the case that isn't it because it is acting weird before the turbos spool.

[justanothrone]

Yea. It's slow to rev. Just changed the oil. It went away for the a few days. Rpm dropped just like it should. Now it's hanging again. Can a dirty air filter or bad trans fluid cause this?

[Indo Rider]

I've had similar issue intermittently. Not really the rev hanging part, but definitely the slow to rev, terrible throttle response part. Just turning the car off and back on has usually corrected it for me. I've battled 2CF6 and 2CF7 codes in the past and think it's related. I don't have much advice, but just to describe the symptom a bit more... when it's acting up, I can tap the gas pedal all the way to the floorboard very quickly and rpms hardly move. When it's acting normally, the same action gets a healthy increase in rpms. If the situation is ongoing, might be worth a throttle adaptation reset if you haven't tried that already.

Edit: Does the car have a piggyback tune?

[justanothrone]

Originally Posted by Indo Rider

I've had similar issue intermittently. Not really the rev hanging part, but definitely the slow to rev, terrible throttle response part. Just turning the car off and back on has usually corrected it for me. I've battled 2CF6 and 2CF7 codes in the past and think it's related. I don't have much advice, but just to describe the symptom a bit more... when it's acting up, I can tap the gas pedal all the way to the floorboard very quickly and rpms hardly move. When it's acting normally, the same action gets a healthy increase in rpms. If the situation is ongoing, might be worth a throttle adaptation reset if you haven't tried that already.

Edit: Does the car have a piggyback tune?

No tune. Stock. What I am guessing is a slow/stuck throttle body. So when the gas pedal is pressed down, the TB opens slowly causing the slow rev up and when the gas pedal is released, the TB stays open for a second slowly closes allowing air still to come in and causing the slow rev back down.