I have a '99 E320/W210 4Matic Wagon that is not starting after getting up to normal operating temperatures. It just had a rad flush, thermostat, pressure test, and temperature settings checks - all is good in those departments. It also had new plugs installed, but not wires or coils.
It starts beautifully when cold, or after a 10-20 minute cooling down period. It runs incredibly well when being driven or at idle until now. Yesterday and today it died while idling in park after lengthy drives (but not in drive at stop signs or light, thankfully). During the rad check-up the other day a check engine code read out "Secondary Air Injection System", but hasn't reappeared.
Additionally, the temperature gauge itself went wonky about four months ago, and behaves very erratically. The needle bounces all over the place and usually ends up as high as it can go before it is stopped by the center/pivot of the gas gauge - even in the first few seconds after not being driven all night, so it's not related to tha actual operating temperature. This was not remedied by replacing the temperature sensor in the cooling system.
MY MB-certified mechanic is scratching his head. Can anyone help?
Try doing a search for Crank Position Sensor... or CPS
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2000 C230K -- Travertine Beige Metallic
2002 ML320 -- Alabaster White
2002 ML320 -- Brilliant Silver - Dad's
1991 300CE -- Blue Black Metallic -- 129,000 miles -- Sold
1981 300SD -- Classic White -- 190,000 miles -- Sold
1977 240D -- Over 300k miles (Wrecked) -- My 1st car
it will tell you if the engine coolant sensor is working,more accurate value than the dash guage.Also run the error codes on the climate control and see if you have failed sensors in relation to coolant temp.Check for stored codes on your obd2 reader(you do have one don't you?) harbor freight tools,$39.00
see if a code is stored,write it down and report back
CPS as above ,is worth checking,first get the codes...
ohlord
"GOT CODES?"
Thanks for all of the great input. We swapped out the CPS yesterday and ran the codes. The only code was the P0410 - Secondary Air Injection Malfunction - so we cleared the code and assessed the voltages coming out of the O2 sensors. Everything reported within range.
The engine is now running fine - cold and hot - and seems more powerful! CEL has not returned, but I understand that it may be tripped after two failures of the Secondary Air Injection System. So far, so good.
Run the climate control diagnostic program 
Linear Mode
