I admit that I'm a complete novice. Got my '89 300e because I like driving it and looking at it. Ran and idled great but after new radiator installation (preceeded by some overheating) idles very low and vibrates - just a coincidence? Isn't there a simple fix, like turning a screw or something. I bought one of those CD owners' manuals which is just about useless. Appreciate any advice.