1998 1.8T AEB: When getting off the throttle, the rpm drops low, the throttle motor tries to 'catch up'.
Works most of the times, but it still happens that the engine dies (not so nice when it happens in the middle of an intersection).

The code I am getting is:

1 Fault Found:
17972 - Throttle Actuator (J338)
P1564 - 35-10 - Under-Voltage during Basic Setting - Intermittent
Readiness: 0110 0101

 

Further observation:
- idle is very stable at ca. 830 or so RPM once it 'catches'
- idle is moving up/down (throttle motor moving) from 600 to 1000 rpm for quite a while (and can lead to engine stall); every time I get off the throttle
- throttle cable (AEB is drive by cable) has a bit slack, but not much
- throttle motor electrical connector removed and cleaned with contact cleaner, no difference
- no vacuum leak found (starter fluid spray test)

 

You have VAG-COM? If so, under measuring blocks (or the Advanced version) in the Engine section you can find out what your throttle angle is. If it's not constant, that suggests to me that there is a reason why it's moving around (correcting A/F for example). You can also compare this to engine RPM and primary O2 sensor voltage to see what's going on.

Another thing you may wish to try is to purchase a used AEB throttle body from a forum member (either here, or Vortex/Fourtitude, etc) and see if that fixes the issue.

 

After a tip on the throttle, the throttle angle goes as low as 3.5 degree, up as high as high as 7.5 (a few times), then settles at 6.1 degree.

 

Can you also check your throttle angle when the engine is off (but ignition on)? I'm not sure what my throttle angle does at idle, but with the engine off my throttle angle is 2.2-2.6 degrees.

Also, my engine RPM tends to bounce a few times for a bit after I clear codes, because when clearing codes this also clears fuel trims. Have you cleared codes recently? If it still bounces significantly after 50+ miles from clearing codes then this can be an issue.

And lastly, when your idle bounces like that, is the car at a stop? If I'm cruising and press the clutch (car still moving) the idle tends to bounce 700-1000ish RPM.

 

Logged the angle. will log angle, rpm, primary o2 sensor (and MAF signal?).