Swap the leads and try that, too -- meter will read inverted sometimes with the leads swapped.

If you don't have an EHA, you have a frequency valve, so make sure that's working, too.

A big leak in the evaporative control system will make you run way lean off idle -- I've had this happen before on our old Ford Fairmont, took forever to figure it out, since the main suction line is closed at idle both by the PCV valve and the purge control line. You can suck an amazing amount of air down a 1/4" line.....

Once I plugged all the leaks, I could suddenly set the idle mixture properly and it stopped knocking on the highway.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!