I am at wits end. I have a 91 300 SL. I live in Arizona. It runs perfectly fine all winter, but as the outside temperature heats up, the car exhibits a recurring problem. It has done this since the vehicle was relocated from the Northwest to Arizona in 1998.

The problem appears when outside temperature is > ~ 90 Deg F.

Problem:
When I start it, the engine fires, reves to ~1200 RPM, then dies. This process repeats for one or two times until it finally stumbles and shakes a bit, then settles into a normal idle. The hotter the outside temp, the more start attempts required.

Once it has started and idling, if I turn it off and restart immediately, it starts ok. If I wait a minute, the process is repeated. It doesn't seem to matter whether the engine is hot or cold.

Additionally, while driving, whenever I accelerate from a stop, or in traffic, it stumbles and lags a few seconds, then catches up and begins to accelerate. More than the normal lag I experience because of the V6 and auto trans. I mean the engine noticalby stumbles.

This vehicle has been to two dealerships and two private mercedes mechanics. Non could solve this problem, however all of them conducted diagnostics inside a climate controlled shop. Non were willing to work on the car outside in the heat.

The Fuel pumps, hoses, accumulator and filter have all been replaced. The injectors have all been replaced. Fuel pressure and delivery have been tested at every shop and check out. I have invested ~5K in attempted correction, to no avail.

I am not an expert on Mercedes, but I do understand engines and it seems like it has more to do with the engine computer control. What ever the mechanism, it is either something that mechanically changes withtemperature to appear at higher outside temperatures, or it is a sensor that feeds info to the system for timing and fuel delivery.

Can anyone help shed light on where else to look.

Can anyone tell me where the engine control unit temperature sensor is located.

Is it possible that the firmware programming for the car is for the Northwest and is not calibrated for the Arizona Climate?

Help Please. This problems renders my vehicle useless, 6 months of the year and has zero resale value.

Thank you in advance for any expertise you all might offer.