I'm working on a '91 350SDL that the guy just purchased. It is showing 168k miles and is a beautiful looking/driving car that is clean as a pin. Unfortunately, it has a cold start issue. I just finished changing all 6 glow plugs (two were inoperative). I did not start the car up cold prior to changing out the glow plugs so I can't tell if there was any improvement or not but I'm sure there was some.

The car starts up immediately but after it has started it idles like crap and there is a good bit of smoke during the initial cold start. I pulled the valve cover and the chain is about 1-1/2 degrees off and it is quite obvious that someone has been changing the oil as they should because everything looks clean under the valve cover with absolutely no sludge build up.

After the engine is up to temp everything is fine. Is the rough cold idle an indication that this engine has gone the way of alot of the 350 six cylinders? Will a compression test provide a definitive answer in regards to this engine holding up its' infamous reputation? Anything else to test/check before I break the news to the new owner?

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Jim