Finally got the hard shifting worked out - so I'm moving on to the odd rhythmic engine surging at idle on my '87 300TDT.

Engine runs great - no issues - lots of power - no smoke out the back of any kind. BUT - at idle the engine has a VERY rhythmic slight RPM surge every sec or so. If you're in the car - you wouldn't notice it - it's only when you have the hood open will you notice this constant - every 1 to 1.5 sec surge in RPM.

The surge is so slight the tach hardly shows any movement - so I'm guessing a change of maybe 100 RPM's up and back down every sec or so. This surging is always there - cold or hot.

Where do I start to being tracking this down?

-John

First I would make sure there are no air bubbles entering the injection pump. You can do this by removing the return line from the injection pump.Submerge it in a container with a little fluid in it and look for bubbles.

My second guess is that it may be the govenor in the injection pump. A good soaking of the pump on the car might or might not help.

I assume you have fairly normal fuel pressure in the base of the injection pump. Unstable idles have been reported with very low fuel pressure but I can remember no cases of hunting from low fuel pressure. Usually the idle is just a little rougher and noisy.

On the back of the IP is a round pod that is vertical. On it is a 2 prong plug. Maybe you knocked it loose fixing your trans? If not pop the plug off. If the RPM changes then put it back on and adust the ELR trim knob on the firewall next to the battery. It is round and has 1-7 or something like that on it. Pull knob and rotate. The more you pull, the more you compensate.

If it doesn't change when you pull the plug then you have any number of other problems. Get on benzworld and check the fsm in the diy thread under 124. There is a complete test procedure but ignore the part about relays as that is for >87MY.

Check your timing and have your injectors poptested either way.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Apparently the elr can cause loping according to a recent post titled changed head on 603. Loping and hunting are not quite interchangable terms but one could be confused with the other quite easily.

ELR controls idle quality. Elektrische Leerlauf Regulierung.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42