Have same prob. 190e 1987 2.3 tried all recomended solutions.. still the same prob. Called Ken at The Benz Store in Atlanta 1 800 631 4170 He said he was puzzled for a while with these problems and finally found the problem....The reostat which is in the heater section . (requires a dash removal) was the culpret.it is an adjustable unit, but after replacing it, things got back to normal.....He sells nationwide and is helpful in a lot of Repair Problems.........Ask for a catalog........He sells alot or reman. items it saves some bucks sometimes.... Pete