940 Non-Turbo

Still hunting the "idling hunting" issue and I note that when I put my gear in reverse in the morning, idling will go down to below 500rpm causing car to rock. In a few seconds RPM moves back up to about 900 and then then starts to idle hunt, fluctuating between 500 and 900 with intermittent sudden drop in rpm causing car to shudder.

This reverse gear phenomenon happens only when the engine is cold. At other times, car will just idle hunt and never stabilize.

I've tried all sort to things from plugs wires, plugs and including a new distributor set, had the injectors treated with injectors cleaner, throttle cleaned and reset, vacuum checked and hoses changed where necessary and other stuff but nothing seems to be able to rid this idling problem. Fuel consumption has also increased and on average I'm getting something like 17mpg.

What else could be wrong, MAF (changed mine 2 years ago)? Diagnostic code reads 1-1-1.

I do notice however that when I insert a half inch water hose as stethoscope in between the 2nd and 3rd intake I could hear some kind of air sound similar like hissing but not as sharp a sound as a real hissing (leak). Is this normal?

All hoses from the breather box to the flame trap checked and there was no leak.

What else to check? Please help.

Thanks for all the inputs.

Laozong