Engine Hunting at Idling

Hello Dr-DJet,

The hunting problem is occurred at idling only.
Normal driving behavior is no problem....

Any other advice would be appreciated.


Best Regards,

JUN
 

Hi Jun,

that is odd as none of the 412 engines has over-run shutoff. That could cause a high rpm hunting on idle.

Which ECU do you have and how much does rpm vary?

Hello Dr-DJet,

P.No. of the ECU is Bosch 0 280 000 037 or VW 022 906 021E.

Idling speed (rpm) has been set 1200 rpm- 1500 rpm. (Otherwise could be stalled)
However, as kind of nature of this car, idling speed is sometime not stable.
This does not mean "Hunting", it means for example, today 1200rpm, tomorrow 1500 rpm or morning 1200rpm, afternoon 1500rpm, something like that.

But now he has the hunting problem.

Thank you,

JUN
 

Hi Jun,

that is correct ECU and it does not have over-run shutoff. Over-run shutoff can cause huge rpm variations if you have large vacuum leaks on manifold.

In your case it sounds like AAV causes that problem. Otherwise you should have stabile rpm in idle and not vary from 1200 to 1500 rpm every day. Of course also a leak on manifold and vacuum hoses can cause such a problem. We use smoke tests to verify in workshops.

Hi Dr-DJet,

Thank you for your advice.
I will disconnect electric wire from the AAV and check if the hunting occur.

I also need to do Smoke test but I don't have its tester.. I will think how to do...

AAV for my car is on the picture.

Best Regards,

JUN

Hi Jun,

yes this is the special VW and Porsche 914 AAV. It is known to be troublesome and tends to stick.