Ok, ongoing mixture issues with my 1987 300E, no cat

Haviing continual problems trying to get the mixture right, the car is running rich as judged by the general exhaust note and the fact it's using a lot more petrol than before. I used to get 20 mpg, which by my calculations is about 7km/litre or about 400km per tankful. Right now I'm getting nearer to 200km per tank.

Another problem I'm having is the mixture seems to adjust itself. Twice now it has gone incredibly rich after running under load. By load I mean with 3 or 4 people in the car, travelling uphill or with golf clubs in the back for more than 20km. The car seems to run fine but when I stop, its sounding really rich at idle and has no power up to 2000 rpm. I solve this by whipping out my 3mm allen key and adjusting the lambda tower screw a 1/4 turn counter clockwise.

I also have an idle problem, sometimes it idles fine at around 800-900rpm, sometimes it drops down to a lumpy 500rpm. Checking the voltage at the ICV, i find that the voltage drops from 6v to 0v when the symptoms occur, I've checked the OPV and traced this to the ECU. I can cause the voltage to drop by rapping the ECU casing, knocking it again brings it back. I've just resoldered some of the connections inside the ECU and so far this particular problem seems to have gone away. I presume this means a new ECU, unless anyone has any other suggestions.

Now, as part of my efforts to resolve the mixture issue, I rigged up a harness to monitor EHA current, and my readings are these:

KOEO +20ma
Deceleration goes to -60ma
Starting (warm engine) +60ma dropping to +3.5ma
Idle (warm engine) +3.5ma
Steady throttle 0ma
Accelerating - anywhere from -5 to -10ma depending on load, dropping back to 0ma

Based on what I've read in other posts, most of the readings are OK, with the exception of idle and accelerating. I'd expect the idle reading to be around 0ma, and I'd expect the acceleration figures to be + instead of -

So, my questions:

How can I adjust the mixture to get EHA current back down to 0 at idle (or -2ma as recommended by stevebfl)? Adjusting the lambda tower seems to have no effect on the current reading.

I've read that there should be around 3mm clearance between the air flap and the fuel plunger. On my engine there seems to be around 1mm or less. Is this likely to be part of the problem?

I've recently adjusted the EHA screw as I've replaced a failing fuel pump and I deduce that fuel pressure is up. I have no way of checking fuel pressure without taking the car to the dealership as noone else on the island has the gauges. Is there any electronic feedback that will help with adjustment?

What's going on with the acceleration readings? My understanding is that a negative current at the EHA means less fuel, is this right?

Why would the mixture adjust itself? Do I need to replace the lambda tower because its not holding its setting or is it likely to be something else?

Sorry for the lengthy post but I hope to get some guidance here. Getting fed up spending my weekends tweaking the fuel injection system.

cheers

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1987 300e manual 250,000 km (sold)