Engine Hunting at Idling

Hello

I blocked the AAV by cork according to your advice.
However, the hunting still occurred.

Common symptom when the hunting occurred is the following.
i. Engine start is OK
ii. Until about 1 minute from engine start, engine run is perfect.
iii. After about 1minute, engine speed drop automatically and then the hunting start.
The above is the same with or without AAV connected.

Voltage for ECU is OK. Main relay and fuel pump replay have been replaced with new 2 months ago at Tuev inspection. 

I am going to change air hoses with new one as next attempt.

Why always 1 minute later the hunting happens, that I have no idea.

Do have any other advice ?
 
Thank you,

JUN

Hi,

an engine in cold start runs very rich. Have you measured exhaust gas in idle and adjusted rheostat on ECU?

Hello Dr-DJet,

Firstly, thank you for your advice.

According to your advice, I adjusted the rheostat at cold starting which I have never done before. 
By doing that the hunting at idling has gone !!

After the adjustment, I drove almost 200km under hot weather at over 30 deg.C, No hunting occurred !! (I will adjust it further to get more better condition)

Again thank you so much for your advice. I also appreciate other colleagues who gave me a lot of advice !! 

BTW, at the end of the test driving, I filled Gasoline and then restarted the engine.
At the time Engine start was difficult that it took longer time for cranking .
May be this is caused by Percolation ?
As far as I know, many people say that this is a typical problem on D-Jetronic, is it correct ?

Many thanks,

JUN

Hi Jun,

well my 450 SL starts immediately with warm engine. When you quickly loose fuel pressure as you described it means that who wil have fuel vaporization in fuel lines. Those vaporized bubbles need to be cleaned out before engine can start.

Hello

Once I measured fuel pressure. 
When I turn IG on, it goes up to 2.1 kgf/cm2 and then immediately drop down to 1.3.
As long as IG key on again, the pressure quickly down from 1.3 to 0.7. 
While Engine in running, the pressure keeps 2.1. By turning IG off, the pressure down to 1.3. 

Is this normal ?

BTW, Yesterday, Engine run is perfect at all situation. However, today, Engine run at idling is uneven and Engine make a bit bigger vibration.
I plan to fuel pressure regulator, do you have any advice ?

This uneven running is caused by possibly the above fuel pressure issue ?
Do you have any ideas ?


Many thanks,

JUN

Hi Jun,

for sure you have a fuel leakage and you need to find out where it is. Can be fuel pump, hoses, injectors, pressure regulator, cold start valve.