OK, I have read many of the M103 posts on 'rough idle'. And done many tests or inspected components. Problem: Cold start OK. Idle at 800 rpm. Then engine heats up to 80C. Then I drive, back off accelerator and engine idle drops to 600, and sometimes dies. Like when cornering, or after a high speed (50+ MPH) run, to a stop light. And on a hot day in July, difficulty cranking a hot engine, until the temp drops (or I call AAA, and by the time they arrive it has cooled and will crank. This is my 1989 300E car, w/ only 105K miles.

Have replaced FPR 2 months ago. Plugs, dist cap & rotor 2 months ago (non resist plugs). Checked kick-down micro-switch OK. New O2 sensor 12 years ago (but only 25K miles ago), Checked/cleaned the PCV pipe (thin one.) But the nipple into the fuel pressure reg is cracked. Carb/throttle body cleaner. Also cleaner onto the air flow meter (inside throttle body). Removed & cleaned the IACV, and tested OK. Tested the action of the throttle plate position sensor. OK, and switches just as plate moves a few degrees. Tested air flow meter (low-high-low) as air plate moves.

The only anomolie is the rear 2-wire temp sender to the FPR. The analog code readout blinks 3 times. The thing ohms out at 3,830 on a cold day (9-deg-C). And after running at 259 & 264 ohms at 79C. According to the book/temp curve, the low end is a few percent below-scale. (Book says 290-370 @80c).

This problem is driving me nuts! But I want to win this one, real bad.

Suggestions? Change the temp sender (so close.. but maybe the computer does not like it?) Anything else to check (short of every tube, hose and wire/harness in the engine compartment? What about the fuel evaporator canister & it's temp sender/switch in the left front fender?

__________________
BnObob (for the fallen flag railroad.)
Artic "Snow" White 1989 300E, 124.030
w/ M103 engine, and 106K orig miles.