Sudden engine idle speed increase! - PeachParts Mercedes-Benz Forum

#1 09-18-2002, 03:15 PM

Hey guys!

I de-greased my '76 123 200D's engine this morning using a commercial car engine degreaser.

Following the spray-on, soak for 10mins, then wash off with high water pressure directions, the engine appeared pretty clean!

Problem is, when I started the car, the idle speed suddenly increased (my model doesn't have a tachometer, but im guessing that it was at least a 300rpm increase!). Im kinda lost as to why this had happened. I then drove the car for about 2hrs in stop-and-go traffic, but still the engine idle speed wont drop to its previous level.

Was it because I sprayed too much water? Or maybe the degreaser or water got into some crevice or somethin? The engine was quite warm (not hot, you could actually 'tolerate the pain' if you would rest your hand on the engine) when I washed it, though it did 'steam'.

Also, I've been wanting to know what you would want to put into the hole with the red cap in the injector pump that says 'oel', and how often?

Sheeesshhh! Hope I didn't damage anything.

Thanks for the helpful advise!

DON

engatwork · #2 09-18-2002, 08:53 PM

I'm wondering if the linkage got moved around and stuck? You want to make sure you lube all the pivot points on the linkage after you clean the engine up.

#3 09-19-2002, 02:07 AM

Will do that... I did notice earlier that even though I let off the accelerator pedal, the engine speed would not go down as it would normally do (but only very slightly).

#4 09-19-2002, 11:23 AM

Thinking the cleaning process must've removed the lubricants on the linkages, I lubricated them again. After removing, greasing, and re-installing them WITHOUT making any adjustment whatsooever, the same problem subsists! The idle speed is still very high (at least 1,500rpm, I reckon).

So I thought the next logical step would have been to adjust the idle speed by adjusting the screw at the air-intake/throttle manifold. Well guess what... the darn idle speed wont go down! This after making sure that the throttle itself is almost close! The screw is almost removed... all to no avail. This car doesn't have any vacuum assisted/power whatever... in fact, it has the old 'pull to start' switch.

Okidoki.... so maybe this problem just coincided with the degreasing. I did experiment with the Injection Pump and I found out that when you pull up the linkage at its side/rear (if you disconnect it from the other linkages), the idle would drop sufficiently, almost to the point of cutting out. Why is that? Could that be it? Rats! My injection pump seems to have a problem!

Could this be because I also popped a quart of 2T Oil on a tankful of diesel (read somewhere here that 2T Oil [for motorcycles, I think] is better than any other oil for fuel because it is meant to burn)?

Lost again...

DON

engatwork · #5 09-19-2002, 02:40 PM

Don, does your car have the little idle adjustment knob adjacent to the steering wheel? Maybe it is "cranked up"?
The 2 stroke oil in the fuel tank should not have caused an increase in idle. I would suggest trying to get an idea of what the idle really is and see if it is within spec.

#6 09-19-2002, 02:54 PM

Ok guys....this is a test for me.

Diesels increase in speed when you add more fuel....injector related....could this be caused by a control valve or vacuum tube being blown off during the cleaning....

I have been spending alot of time with my vacuum lines and linkage....check to see if any lines are hanging down.....

Nathan

#7 09-20-2002, 11:48 AM

Hey guys!

My car doesn't have the idle switch at the dash anymore, or at least the wire that goes from there to the throttle. It broke years ago and i didn't really feel the need to replace it (never had any effect anyways, and I never fiddled with it).

Now the vacuum tubes, I checked but nothing seems a miss. I've been told that it might have been bad fuel, or more like diesel mixed with gasoline! There seems to be considerable knocking when you ease off the accelerator after flooring it. It also appears that the diesel is a bit 'thin', not as 'oily' as you would expect.

What I'll do is I'd use up this tankful then fill it up with diesel from another station. If by then the problem wont disappear, then... obviously something broke!

Thanks again!

mreid · #8 09-21-2002, 01:05 AM

You obviously have a linkage problem. Check carefully all throttle linkages from the IP to the pedal. Maybe even a gob of grease where it should not be.

#9 09-25-2002, 12:07 PM

Just to wrap it all up, I was told after I decided to get professional help that it was the diaphragm. After it was fixed, the idle speed dropped to the normal level, plus I aint seeing smoke even when flooring the engine. However, I think I've lost some acceleration power... but then I guess thats a little sacrifice so as to reduce the diesel smoke to a minimum. After everything, it seems that the true cause of the problem just coincided with my engine cleaning... kinda makes you not tinker with the vehicle for a while.

Thanks again guys!