Strange throttle behavior

[dboard9]

In neutral, pressing throttle slowly has an odd effect:

Press on pedal to increase engine RPM from idle up to say, 1500 RPM, and after 5 seconds, RPM returns to idle with same throttle position.

This can be repeated until pedal is floored and engine is still at idle.

I discovered this because I was trying to listen to a new turbo whistle... engine has about 200,000 miles on it, running fine with NO turbo noise until a week ago.

Is this a vacuum leak and not turbo noise?

 

[Typrus]

Mine does it too.
I'd suspect its a pcu thing? Maybe you have a BK and BK's are evil? My BK is evil...

I'm also curious. I had suspected worn throttle position wiping surface, but it works fine in gear....

 

[Diesel Dude]

Are you guys stepping on the brake while you are pushing down on the accelerator? If so, this is normal behavior for a fly by wire throttle system on many of the TDI's. I understand that it is a failsafe so that if there is a malfunction in the throttle that you will stop any unwanted acceleration by applying the brake. VAG is very sensitive about this after the problems that were associated with various Audi models in the 80's.

 

[dboard9]

I wasn't stepping on the brake, I never use the brakes!

Seriously, only the parking brake was applied.

And sorry, - I need a glossary here!
PCU = ?
BK = ?

 

[AccountingTroll]

IAnd sorry, - I need a glossary here!
PCU = ?
BK = ?

PCU, I think the original poster meant ECU, Engine Control Unit.

BK, this is the code for the original ECU in early Passat TDI's. My car still has the original BK unit. It is less tunable but does not give CEL's for every little thing. This can be good and bad. Good because you can take out the EGR, bad because it becomes harder to diagnose some problems.

Back to your car, the clutch also has a cut out as part of the cruse control system. My car with the original BK does NOT do what you are describing but I think newer ECU's do.

YMMV

 

[Typrus]

Sitting in my driveway, parking brake on, clutch out, in neutral, it does this. I have a BK.

Some manufacturers say PCU- Powertrain Control Unit, or sometimes PCM, Powertrain Control Module.
I say whatever comes to mind. They all mean the same thing.