I have a model year 2000 E320 4-Matic sedan with 186,000 miles. The car runs great and recently passed the Illinois emissions test. Under certain conditions the low fuel warning light begins to flash and shortly afterward the check engine light also comes on. This occurs when the weather is warm and the fuel level is below roughly 1/2 tank. The light does not come on when the tank is full above 2/3 tank or when the weather is cold. The light comes on and flashes on warm days when the engine is at idle for several minutes. On a long drive at steady highway speed the light does not come on at all, even down to 1/8 tank and in even warm weather. When the weather is cold the light stays off under all conditions. I have replaced the gas cap but the problem still exists. I have been reading about similar symptoms resulting from a faulty purge valve on the evap canister. I would like to get opinions and recommendations from the forum on how to troubleshoot this problem.