Uneven Idling at "D" range, Not at "N"

Hello 

I own VW412 with Automatic (1.7L D-Jet).

After over an hour driving under high outside temperature (Over 30degC), Suddenly idling become poor at Automatic gear with "D". But when I shift to "N", idling back to normal.
Other driving performance is no problem at all even when this problem is happening.

Poor idling : Engine RPM is up and down repeatedly. It is not like a normal hunting. It looks Engine is weak. Not stall but Engine RPM become very low and goes up again-

Every time when this problem happen it is after driving over one hour and Engine oil temperature is around 90degC. ATF quantity is OK as far as I checked according to Owner's manual.

Does anyone give me a tip for solution ?
If you need further information please let me know.


Best Regards,

JUN

BTW, I posted some questions in the past, by your advice I could fix the problems I had before. Thank you.

Hi Jun,

that is a difficult one. D-Jetronic has no idea whether your AT is in D or N. So there is nothing I can suggest as a possible reason why this symptom would happen in D and not in N.

I assume that you have a US 412E from 72 ? They have some relais for rpm, an air valve and a 2 way valve connected. If they leak they can cause troubles like false air and hunting engine.

Dr-DJet,

Thank you for your advice. 

Mine is VW412LE (1973 model) for Japanese market with RHD. 

Ok, I understood that D-Jet has no ideal if the Automatic is at D or N...
This is very good information. This means D-Jet system is not the cause of the problem.

I will need to check if some function which may cause this problem is available on the AT system as you kindly discribed.
It is strange....

Thank you!!

JUN