Hello i have a 82 300sd with 318K miles.

Ok the symptoms ive been having are:

1. Rough starts. It starts easily enough but idle is rough and needs a higher rpm to smooth out for 5 sec or so. then the idle will still oscillate between 7-1000. Once it warms to Op temp the idle is fairly smooth.

2. once warm if i just tap the accelerator a tiny bit it will rev up 3K and pause for a second before slowly come back down(more than a normal rev, like my foot wont even be on the pedal and its climbing before a distinct pause and slow down) .

3. It also sometimes Revs up after driving around the block when i shift from Drive to park, revving up to 3k and slowly coming back down. Or its happened when ive idled for a couple minutes and turn it off(about scared me to death thinking it was a run away.) But these two symptoms don't occur together, its one or the other thus far.

I suspect these issues are the injection pump, and i am not looking forward to pulling that in this cold weather.

But please chime in if you've had previous experience or knowledge with these issues. I really need the car on the road again.

bump.

What is your history with the car? How long have you had it? Have you done any service recently? What precipitated these changes?

Have you ever set the linkages? (I doubt that is your only problem, but it is an easy place to begin).

Is this SD new to you? or have you had it for a while?

Rough starts could be Glow Plugs, some may not be working.

Mercedes Diesel Glow Plug Repair

When was the Valve adjustment last done? It does wonders and especially now that cold weather is setting in. If it has not been done for a long while, you may have to do several close together as the carbon wears down and they get out of adjustment.

Mercedes Diesel Valve Adjustment Procedure

The Ball and Sockets on the linkage could be rusty and be in need of lubing, which could be the problem with the RPM issue.

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Definitely check linkage first to make sure all is smooth and nothing is binding and or causing linkage to move. maybe even disconnect the cruise control linkage to make sure somehow some way its not trying to pull the throttle linkage.

Once above is done, I'd then back off the idle adjust nut to the point where the idle is low, but the internal governor in the ip has complete control over the rack. In this condition at idle, the internal governor should have complete control over the idle; idle maybe lower than 700, but that's ok for troubleshooting.

The only way the engine can speed up at this point is either for the rack to move via the internal governor, the foot pedal, or injection of fuel (oil) from an undesired source.

Like already mentioned, history is needed if available.

Problem may still be there, but its a start to id the root cause.

On another note; I once had a car (not a Mercedes) that would try to run away when accelerator was pushed. Turned out to be a motor mount that when torque developed, the engine would roll off the left mount, causing the throttle linkage to pull even further and apply even more throttle. Not sure this can happen to a 123 or 126 with the way the linkage is configured, (I assume a 126 is similar, but not quite sure as I've never owned one) but easy to check. Just crank it up and manually throttle it up using the linkage under the hood and see what the left motor mount is doing. You should see it marginally rise and fall within the limits of the motor mount; no separation.

Hope this helps; let us know what you find.
Mike

Hello Phslion,

As masc243 and charmalu suggested, adjust your valves and then do the throttle linkage, As for the latter, go over every piece very carefully and adjust according to the Service Manual (section 30-300).

One area often overlooked is the Injection Pump (IP) rack damper bolt. You can find this at the bottom of the IP just below the Vacuum Control Valve. IIRC it is a 14mm bolt head with a lock nut. This bolt has a spring loaded pin in it the purpose of which is to act as a sort of shock absorber for the rack in the IP. The bolt allows you to adjust the preload on the spring and the lock nut to fix the position. Needless to say the spring looses tension over time.

I would suggest measuring the bolt head to housing distance, then loosen the lock nut and back out the rack bolt. Check the pin and spring to see what condition they are. Then return the damper to the IP. Adjustment is tricky, with the engine idling you turn it in until the idle stabilises. BUT make very small turns in or out and wait 10 or 15 seconds to see how the idle responds. Rev the engine every once in a while to see what the idle speed is. All these adjustments should be done when the engine is warm.

BTW don't rely on your tach unless you are very certain it is accurate. If your car has spent any time in a hot climate the electrolytic capacitors (electronic components) dry out. Replacements are easy to find and replacing them is not that difficult. To check the accuracy of your tach, do the math to calculate what your engine RPM should be at a given highway speed. Mine was reading 300 RPM to high at 120 kph (75 mph), which lead me to replace them.

I digress. Adjust your valves, inspect the throttle linkage very closely and then adjust the linkage (you must use the MB Service Manual 30-300), then check the Rack Damper bolt.

If you don't have this section of the Service Manual, send me a PM with your e-mail address and I'll send you a PDF copy. The file size exceeds what I'm allowed to attach to these messages.

The URL below is for the Rack Damper Bolt, they are not cheap, you may be able to find it for less money elsewhere.

https://**************.com/store/617-turbo-diesel-rack-damper-bolt-special-o-ring

Hope it helps and good luck with the troubleshooting.

I've owned the car for the last 5 years and my father before me owned it for around 15. for the last two i really have not driven it much, i got married and we had a newer vehicle and functioned well with one car so the 300sd kinda sat for a bit, getting run every 4 months or so.

but over the last winer i started fixing the issues its had. Mainly tired suspension and always a ***** to start in the winter, oil leaks.

I started with the worn rear suspension. New rubber, shocks, flex discs, rotted muffler, and brakes when i was down there.

Next moved to the front. brakes, uca, new turbo rubber to stopped the crazy leaking, new exhaust flex pipe, clutch fan, coolant flush, glow plugs.

It was coming together but still was difficult to start. Oh yea injector nozzles changed before all this started. I decided to pull the pre-chambers due to one leaking and clean them. replace the oil cooler lines and oil filter gasket while i was at it.

my memory is a bit fuzzy when the idle surge started occurring.

but in my efforts to get it o go away ive done multiple valve adjustments, multiple drip timings, and even went over the throttle linkage adjustment specs.

i honestly took a 4 month break because i got so frustrated. my next step was to swap a junk yard injection pump in and see what symptoms change.

but ill do my best to double check your responses and post what i find.