My 89 300E (127K) has recently lost its "choke" when cold. Starts right up and immediately the idle drops to 400 rpm +/- and is very rough. If I hold the accelerator to 1500 rpm for 30 seconds while it warms, it will idle and drive just fine.

I'd like to check my coolant temp sensor but cannot find the resistant specs in my UK version Haynes manual. Can someone please post the specs? I'm assuming this sensor is the culprit and I believe it's the green two lead sensor closest to the firewall on the cyl head. Pls correct me if I'm wrong. FYI....OVP, wires, plugs, dist, rotor, fuel filter, coil, etc., have all been replaced recently.

I also believe there's another sensor (ignition?) located nearby but I've heard that if it fails the car just simply won't run. If you believe that this one is worth testing, please post the specs also (if you have them)....is it the next two prong sensor moving toward the front of the engnie (there's a small one prong sensor in between them)?

Many thanks.

Hi Mike
I recently posted a thread about this.
I had similar symptoms and found a bad connection on the sensor.
If your 300e's sensor is the same as my E200, and I think it is,
then it should be 325 Ohms @ 80degrees C
1200 Ohms @ 40C, and
6k Ohms@0C.
Mine went totally open circuit, infinity Ohms, led the ECU to think the coolant water was minus God-knows-what, and went to full rich. As soon as the lambda probe caught up, its sorted things out.
So it started fine from cold, but hot starting was really difficult.


Hope this helps

Good luck
Barry
E200 1994 108k miles

Also look for 3.0K at 15C. That would be a normal cool weather running value

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator