This c230 has fuel detonation at idle. The egr does its job so the detonation does not continue when leaning on the engine. You guys who wanna say no car detonates at idle are wrong! Its not a bad noise but the engine just ain't runnin sweet. You know its detonation because when you put on the cabin heater and thus get a temperature drop the noise (detonation) stops. Some "experts" say the car is running inside its teperature specs. In traffic this car gets up to 95 - 98 c. The temp sensor has been replaced and the readings between old and new didn't differ that much - so there's reasonable expectation of some accuracy. Is there top cylinder carbon buildup? I've run several cans of top cylinder cleaner through and also did a pretty heavy water injection session. The detonation reduced a good deal after the cleaning but it ain't gone. Is there something substandard in the cooling system? Radiator is hot all over - no sign of clogging. I replaced the electric fan relay (there is no viscous fan on this one). The fan motor has no obvious problem. At highway speed the temp comes down to the thermostat temp of 87 c. If you pull over and listen to it idle the detonation doesn't start up until you let it idle for 5-10 minutes and the temp comes up. The problem seems to have gotten worse with the change from mtbe to ethanol. I've noticed that there's no more 97 octane out there - maybe that would solve the problem. This car was made before ethanol becam a fact of life in fuel. So guys what do I do. My wife and my mechanic say I'm a little nuerotic but I don't care what anybody says - your motor ain't right if its detonating. Maybe some custom radiator would drop the idle temp to 87c. Or should I just forget about it?