I have an 89 300sel that had/has overheating issues though I cannot get the gauge to rise above 82. The idle runs at 700 rpm then surges anywhere from 1000 to 1800rpm all on its own Oil gauge drops as rpm does. Car runs fine on road but will die occasionly upon deceleration and slowing for a sharp turn. I have read and read but seem to not be able to come up with an answer. My aux fan does not seem to be working also....

Can I run this car for test purposes without a thermostat?

Thanks
Warren

If you have heating issues the water temp sensor will not give the ECU correct information to correct the idle. Although your idling figures suggest that this is something other vthan the sensor.

Get you heating issues sorted out first. Then go from there.

I have a leak in my cooling system ( plastic neck broken off from radiator). The idle and fuel consumption is all over the place. But the idle is not as bad as yours.

Thanks for the response...I just don't get it, We ran that car for an hour, with cardboard in front of radiator, everything on, and it went to 84 C and no further. then the little plastic holder on top of the radiator( goes to expansion tank) popped up, spraying out. Still surging but erratic. I did get some condensation from tailpipe for the first time.......
Warren