Hello,

Apologies if this has already been addressed elsewhere. I haven't been able to find much. Long time forum user, first time poster. Thank you to everyone who keeps these up. They're hugely useful.

My issue is as follows:

Recently bought a 1979 300CD. I've owned a number of Mercedes Diesels and this one is in pretty rough shape. Basically original everything except glow plug setup and hoses used for (possibly) running WVO from a tank in the trunk. (Was given story by P/O about how it was not a WVO tank...)

Work done: replaced fluids, filers, oil, replaced hand primer pump. Diesel Purge, oiled linkage.

The car smokes quite a bit on startup, then seems to idle well for about 5 minutes, and then usually starteds surging or fluctuating. the surging is usually consistent. up for a few seconds and then back down again. sometimes after i drive it around for a while it stops doing this. generally it seems to get better after the car has been driven on the highway, although sometimes it does not and will still do it when very hot. One of the injectors also nails intermittently, but this seems not to be directly correlated with the idle issue. I.e., often the injector will stop knocking and the idle will continue to do strange things. Also, sometimes at idle it will be idling consistently (not rapidly fluctuating), but will have apparently increased so that when i shift it from park to drive the transmission clunks into gear because it is idling too high.

Wondering if this is a compression issue, or if there is some vacuum issue or fuel issue that could cause these symptoms, or all of them combined. Sorry if this is too vague, just hoping to find some direction before i start spending money trying to randomly troubleshoot.

Thank you for any help in advance.

- Eric