1990 300TE, same problem. Change the coolant temp sensor and make sure the proper spark plugs are installed, many idiots will put Platinum plugs in, wrong....but the coolant temp sensor is very important ($35). these 2 items completely solved my very same problem, the Bosch Copper Pluses are around $3 each so the whole thing could be less than $50 out the door. Also, make sure the hoses are all OK.....