Well I got my Evolution 1 back together this weekend. New injectors, airflow meter all new rubber etc etc.

At first with the EHA connector and the harness from the airflow meter pot connected she wouldn't barely hold an idle and the idle would jump from 500rpm to 1500 rpm - exactly the same as before. Raarrgghhhh......

Except of course the airflow meter pot _was doing it's stuff correctly. I was a little stumped, as when I removed the idle speed regulator she would hold a warm idle no problem. Began to think it might be the regulator after all but it just didn't ring true. Decided to RTFM and pulled out my Bosch FI manual by Charles Probst.

Seems that the factory does not set the air flow meter's zero position and basic position. Maybe because they can't as both positions have to be checked and set with fuel pressure. Zero position of the sensor plate is at the top of the machined vertical cylinder. The plate side furthermost from the fuel distributor. The airflow meter plate must be at the very top of this tiny cylinder. The cylinder is only 2-3mm in total height. My plate was about 3mm above the zero position. I dropped the sensor plate height by driving in the guide pin adjuster a mm or so, this put the plate in the correct place.

For basic position I depressed the plate until I felt the resistance increase, ie when I was moving the control plunger in the fuel distributor. It was way off, no gap between zero and basic. I adjusted this by leaning out the lambda adjustment down to basic position which is the bottom of the "cylinder" I mentioned above. All of these tests were done after I had run the car for 30 seconds, switched off, ignition on to keep pressure in the system. At the bottom of the cylinder, the max allowable distance between basic position and zero position is 2mm. At 2mm she was too lean to start. I richened it up approx. 0.5mm, ie 1.5mm zero-basic and she started smoothly. A bit of further tweaking by watching the EHA current and duty cycle and I now have her running at 45-55%... VERY HAPPY. It seems I have finally exorcised her demons. All digits crossed!

Just thought I'd report back here my findings and result. Whats really weird is the original air flow meter I removed was not correctly set for zero position, and it exhibited the same weird up/down idle! The potentiometer was still toast of course, but it seems that the zero position was causing all the idle strangeness.. Be interested if anyone else can corroborate this!

Cheers,
Neil
87 190 E
89 190 Sport Evolution (Factory)