rpm going up and down when engine is cold

Hi Everyone

My MB Coupe 107 (023) chassis has M 116 3,5 L V8 engine equipped D-Jetronic.
Lately I have been experiencing 'hunting' of the engine.
When the engine is cold the rpm goes up and down until temperature goes over 80 degrees celcius.
To avoid hunting I have to keep my foot on the gas pedal.
When the car goes downhill the hunting fades below a certain speed.
What could be causing the problem and what is the remedy

Hi Juan,

that sounds like a hanging AAV (auxiliary air valve). Have a look at jetronic.org/en/d-jetronic/aav . You will also find a video there showing the "hunting". It is due to a slowly moving AAV that keeps open for too long. Then rpm goes up until ECU activates over-run shutofff in idle. We call it sawing as rpm is then like a saw tooth.

Hi Volker,

The AAV was uninstalled and cleaned with Brake Cleaner and re-installed. When I started the engine next day engine was not hunting anymore. I will try again this week.
There is another issue I want to raise. The gas pedal is a mechanical set of springs and other metal pieces. Is there a manual to set it to the factory settings?

brgds
juan

Hi Juan,

well you are lucky if brake cleaner really helped. Normally it cannot reach out to the areas where piston hangs and also not compensate weaker expansion element.

You find complete 107 SL Workshop manual above in menu.