My '82 300SD has developed a weir quirk. It starts fine, has good power, especially with the Dawes boost controller, and normally idles great except when very hot. I don't mean the coolant temperature is hot, it could be a little over 80C like it was this morning, but after the engine has made a good run down the freeway.

Using this morning as en example, she starts and runs fine around town all the way up to operating temp. I get on the freeway and do 80-85 for about 25 miles to work. Getting off the freeway, it's loping badly, temp gauge reads about 82C. If I sit and let it idle for a minute, maybe less it depends on how hard I've been driving it, the idle smooths out to normal. If I just stay around town or avoid high speed (>75mph) freeway runs, it idles fine. It only does this when I've been cruising fast for a while.

I think compression is Ok though I haven't tested it. It started right up in the mountains this weekend at about 10 degrees and 7000 feet and has plenty of power. My dad's 300D lost compression and this car acts nothing like that one.

I never have to add oil between oil changes. Oil rings seem Ok at least.

I get about 21 mpg, 22 at best.

I have no idea when the injectors were last changed/cleaned.

I adjusted the valves about 5K ago. (That help her run much better at the time)

Replaced the fuel filters about 2 months ago.

There are no fuel leaks that I can see.

I tweaked the alda up 1/2 turn initially when I installed the boost controller but backed it off to about 2/3 due to smoke. It didn't seem to help the smoke. This car was never a bad smoker before and I don't know if installing the boost controller made it worse, my girlfriend drives this most of the time.

Anyway, I'm leaning toward a bad injector but have read here about the IP needing some seals or the likes?

Any help diagnosing would be appreciated.

Thanks,

Frank

__________________
'82 300SD