240D: temporary idling like a racehorse
 

1979 240D, 179k miles...... Its my parts car, been sitting undriven 6 weeks.

Took it on 70 mile spin yesterday and the idle was high for the first 1/2 of the trip. It idled so high that I had to slip the clutch with my other foot on the brake at red lights to slow it down....... No such high idle situation had ever occurred before it was parked in January.

But then it miraculously calmed down and resumed idling at normal speed for the return trip!

There is no alda, weird vacuum/electric regulating device for fuel/air and no crazy oil separator breathing apparatus on this '79 240D. There's no cruise control and nothing looked sticky with the throttle linkage or idle adjust.

Fuel is ordinary truck stop #2 diesel with about 4 ounces of Diesel Kleen additive used at every fill up. And the vehicle has no maintenance issues re/ filters, valve clearances etc...... What caused this *temporary* high idle situation??

Lube all linkages.
 

Run away diesel, why does it happen?
http://www.peachparts.com/shopforum/showthread.php?p=824840#post824840


Have a great day.

Thanks but it was not a runaway diesel, idling did not go through the roof. Instead it was stabilizing 200-300 rpm's high. Over the first 35 miles it called for some interesting shifting techniques with the 4-spd, thats for sure. And now the problem doesnt exist at all. Am wondering if fuel separation is possible where more flamable stuff drifted to bottom of the tank over 6 weeks of standing still.

Maybe you should double-check all of the linkages and the attachment of the idle adjustment cable. Since the problem went away and hasn't come back my first thought would be that something in the throttle linkage was hung up. You have been around the 240 longer than I have though. Just my .02.

Best guess:
 

Linkage corroded + minor oil leak down through valve stem seals + a micro diesel injector leak = soaking the cylinders for months = elevated idle once started.

Yeah I know what you mean about precomb chambers getting soaked and then the engine taking off into orbit. Have seen this happen from stone cold start with idle adjust turned up - where the engine suddenly takes off if unattended.

Weirdness is the high idle situation lasted so long and then dissapeared...... twig or stick caught under the hood? Heck it could be anything.

Just the hidden power of the 240d trying to emerge???Has someone found it at long last? Next time if it does this just get out and see if you can shut the linkage down farther by pushing on the injector pump arm. . If so just lube up the linkage and check it. The problem went away now so I would not lubricate and check the linkage until after It happened the next time if it does .Providing it is not a safety issue of course. Probably caused by sitting around too long plus linkage not lubricated for a dogs age..That way you know what the cause was for certain. Having some difficulty with the concept of working to keep a 240d down while sitting at a stop light. It sounds like an episode right out of the twilight zone. When you find the mysterious source of this extra power send some of it to me for one of my 240ds. :D

I agree, it sounds like the linkage was sticking for a while, them loosened up after a bit of driving. Did the peddle feel stiff? Try some spray lubricant on the linkage and the idle cable.

Just went back and read your post. If there is a breather line from the vaccum pump to engine intake system have a quick look for evidence that there has been oil in the line. This 240d is one of the older ones it seems and might have that feature. Also noticed you said linkage looked good and that got me thinking as well. Any sign of a lot of oil in the air cleaner box? If you are going to use that engine I would consider keeping a fire extinguisher of the right type on front seat or floor until I found out what was going on. If the base oil was getting up top it would provide a method to smother the engine if it got out of hand. Pretty extreme I know but really sounds like you were dealing with more than 200-300 revs higher than normal idle when this was going on.