Whats wrong? (280 SE)
 

My w126 280 se wont idle when its at Normal operating temp (80°c) i also noticed a lot of blue/white smoke coming out of the exhaust.
And in order to keep it going at stop lights i have to rev the engine to about 1500 rpm and sometimes it dies when taking a turn wich can get scary sometimes and when it dies i have to keep the throttle all the way in to start it .
I just replaced the powerplant witha a 2.8L from a w123 with about 300k km on it wich i dont think is old for such a engine since my old engine had a little over 400k km.
what could be wrong? fuel pump, filter, vacum lines, ........

Blue/White smoke means that oil gets into the combustion chamber, I think. That probably means a couple of things...

Worn out piston and sleeve, or gasket? I don't know much I'm sorry.. but definitely it's burning oil..

*I think* - really not sure

As Ice-Benz says it could be burning oil big time, alternatively the symptoms you describe can occur when over filling the engine with oil. You may have overfilled when replacing the engine. Mercs seem particularly sensitive to this. Check your oil level and drain off if necessary.

Im also thinking head gasket.....check your expansion tank for normal coloured water. If the water has turned a chocolate colour then the gasket has gone

Thanks for the replys,
i checked the oil and water both are ok but i had a broken monovalve, so this mornign i replaced it and fiddled withe the little screw on the manifold (the one that sets the idle speed) and the car is smoking but it runs. 7,9,13.

Could a broken monovalve have anything to do with the car not running at idle speed?

Arrrgg, i have the same problem again today but now its also leaking oil like nobodys business and smoking alot.

If this where any other car i would alredy have pushed it off a cliff! but im thinking about puting in a 5.6L M117 engine but for now i would like to keep the M110.