G'day Folks,

I'm back pulling out my hair trying to get my M102 to behave properly.

The problem is this:-

The air flow potentiometer has been changed. I have been helped out by someone who sent me a bit of information out of CIS saying that with the engine off - ignition on you should have between 0.2 and 0.5 volts.

Simple enough eh?

Other information on the interweb says you need to have 0.7 volts (all DC readings!) when the engine is at idle (about 750 rpm) =>

SG-Motorsports Air Flow Meter Potentiometer Replacement

OK - also simple enough - well it is a pain in the arse but it can be done.



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Trouble in paradise (1)

If I adjust the potentiometer with the engine idling (as most people seem to do) then all is OK until the engine temperature gets about 60 degrees C when the switch over valve for the timing kicks in and things get even worse when the engine temperature gets to "normal operating" of 80 degrees C =>

I get a 80% duty cycle error code on my multimeter (which in Mercedes speak means 20% error code - typical eh?) which corresponds to a WOT sensor problem (==20% error code). Now I've had that sensor in bits and checked it over so many times (with and with out dodgy leads) - I am sure there's nothing wrong with it.

So I don't believe this error code in terms of a problem with the sensor or the wiring.

On a warm engine >80 degrees C - Idle is high => 1200 rpm as though the air idle control valve is disconnected - but I this is due to the error code

Adjusting mixture screw has little effect (until you turn so far that you starve or flood engine)

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Trouble in paradise (2)

If I ignore the "on the fly" setting it at idle advice in the link above and follow the CIS instructions I get a different kettle of fish.

Ignition on - engine not running - set air idle potentiometer to 0.2 volts (or the other end of the range at 0.5 volts) and I get about 2 volts showing with the engine running at idle.

Engine runs at a good idle for all temperature ranges. 750 rpm - a bit jumpy

The duty cycle is at about 50%

BUT

It is like the computer is stuck in warm up phase so it thinks the engine is colder than 60 degrees. The duty cycle always seems to be at 50% during warm up.

Adjusting mixture screw has little effect (until you turn so far that you starve or flood engine)

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So questions


1) Should I believe the error code with the air idle potentiometer set at 0.7 V with the engine at a cold idle?

2) Should I believe the CIS instructions and carry on looking for reasons for why the ECU seems to be stuck in warm up phase?

3) Was the last generation KE CIS system so different from the slightly earlier KE systems?


If anyone can help - that would be great - I'm running out of hair to pull out on the top of my head - I don't want to start yanking out stuff "downstairs" too!

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!