'80 300SD Help with a loss of power, accelerator "sticking", engine revs in Park

[WrightSounds]

I recently purchased a 1980 300SD (here's my introduction post: http://forum.w116.org/test-drive/newbie-from-portland-or-saying-hello!/ )
The car was running fairly well but was taking a while to warm up so I replaced the thermostat and it is MUCH better now.
The prior owner kept great records of previous work but while looking through them it seems there hadn't been a valve adjustment in a while
so I took it in for one (also suggested by some forum members) last week.

When I picked it up the car sounded better. Engine sounded smoother although the idle was higher (around 1,000-1,100). It also had better acceleration.
After a couple days the high idle started to seem a little too high. Like when I let off the brake while in drive it jerks a bit unless I slowly let off on the brake.
My driveway slopes up and I no longer have to give it any gas to make it up to the top where before the valve adjustment I did.

So today the family and I took a short, 8 mile trip on the highway. Car ran grrreat. 2 hours later while on the way home I lost power and rpms while going up an incline. I had the gas pedal to the floor (for the first time since buying the car) and the car wouldn't go past 50mph or so. Then when I let off the accelerator it was as if I didn't. I'm pretty sure the car was still accelerating even though my foot was off the gas. I then hit the brake and the revving stopped.

I got off the highway and drove 20-25mph home, keeping the rpm down. When I pulled into my driveway and put the car in Park the RPMs revved as if I was
pushing the accelerator. At that point I just turned the key off and went inside and took some xanax.

Now I'm obviously heading back to the mechanic first thing tomorrow but any ideas? The air filter is brand new. The fuel injection return hoses
and inline fuel filter and hoses were replaced 2 years ago (16,000 miles ago). Could it be the spin-on fuel filter? That was not replaced when the other fuel work was done.
Anything else is beyond my major remedial understanding of cars but hopefully I can answer questions if you guys have them! Is this a result of the valve adjustment?

THANKS!
Matt Wright

[JasonP]

I'm still new at this but I'll throw in an idea. Perhaps your pedal or linkage is sticking? It's worth a look, but probably not the cause of you losing power uphill.

There seems to be an idle adjust on the dashboard - mine is stuck and has not moved since I bought it. But perhaps you could play with that.

[ZCarFan]

I'd check the accelerator linkage thoroughly before starting the engine again.  It sounds like something has gone awry in there that might explain both the lack of power and the uncontrolled engine speed in neutral. 

Sounds like you should replace the filters too based on mileage, but I bet your main issue is the accelerator linkage.

[WrightSounds]

Can I ask how to check the accelerator linkage? (novice  )
It's the same thing as the throttle linkage that I found in the handbook, right? http://handbook.w116.org/Engine/617/30-300.pdf
-Matt

[JasonP]

Yup. Just play with it. If you can, have someone sit in the car and push the gas pedal (with the engine off), and watch how it moves back and forth. Then you can use your hands. See if it is sticky. Axle grease is recommended for all of the ball-and-socket connections.

Not a month after I bought my car, I was driving home at night and the accelerator pedal COMPLETELY stopped working. I was on the highway, and it just went to idle and stayed there. It was dark, it was late, I thought the engine was a gonner. So I just got out and looked at it, and had my friend push on the gas. None of the linkage was moving - then I saw that one of the linkages across the top had come unscrewed. So I screwed it back together and that was that.

[WrightSounds]

Word. Freaky story. Thanks a ton for the explicit instructions (like the with the engine off part). Just last night I was watching the MercedesSource YouTube videos and the last one I watched was about lubing all sorts of things (sunroof, hood latch, seat runners, etc) and one of them was the connections at the linkage. Kent used a little syringe in the video to work it in there nicely. I'll definitely check this out. Thanks again.

[JasonP]

I saw those syringes! I want some too. Hopefully I can find 'em at Walmart or something.

[WrightSounds]

Here are two things I use in my guitar repair biz:
http://www.micromark.com/pipettes-pkg-of-20,8119.html
http://www.stewmac.com/shop/Glues,_adhesives/Supplies:_Applicators,_syringes/Pipettes.html?actn=100101&xst=3&xsr=917&tab=Pictures

I use them mainly to flow super glue into tiny places. Not sure how well they'll work since the hole is rather small. I feel like those syringes that
Kent uses will be in any Rite-Aid, Walgreens, etc. Or Walmart 

[WrightSounds]

You guys are awesome. Definitely the throttle linkage. I popped the hood and saw that the longitudinal regulating shaft (I think that's what it's called) had slipped right out from where it should be. Here's a pic:



I followed the shaft back toward the car and noticed these two bolts were really loose.



After tightening the bolts I slid the regulating shaft back through the holder. I realized that something had to be holding it in place when I saw the indentation at the end of the shaft:



So I checked the service manual in the Library and found a diagram that, sure enough, showed a c-clip lock washer over the end of the shaft. Lucky for me I have a wide array of sizes of lock washers that I use for my guitar repair biz so I measured the diameter of the regulating shaft and found a lock washer. Then I cut a small section out so I could snap it over the regulating shaft. It worked perfect the first time!



I took it for a drive around the neighborhood and then on the freeway for a couple of exits. It ran great. The gas pedal is way more responsive. The idle is not as high either. Maybe since all this linkage was loose it was messing with the idle?

My last, and most important question, is should the mechanic come across this potential linkage problem while he was doing the valve adjustment?

THANKS!!!
Matt

[ponton]

He definitely did since you have to take that stuff off to get the valve cover off. Glad to hear you got it fixed.

Ian

[JasonP]

The great thing about these cars is that they are understandable. I hardly knew anything about cars when I got mine, but after the requisite major work done at a local shop (ball joint, tie-rod, flex-plate, new belts), I started to force myself to learn it. It really isn't hard, it just takes time. And it makes sense. These cars are like steampunk, 19th century contraptions that work on vacuum, electricity, mechanics. All very Newtonian. And nothing is really hidden. It's all there to see.

And the online help, like this place, is phenomenal. I think people here who do it for fun are better than 90% of the mechanics out there who do it for a living. For one thing, Mercedes doesn't really train their staff anymore on these old cars. And for the shops that do work on them, they also work on VW, BMW, Porsche etc., so they don't really have the intimate knowledge of just one model, just one engine, or the care, that we do.

I don't know if you plan on working on it yourself, but learning it will be of great help. You kind of have to keep on eye on things when you take it to the shop. Things like this happen a lot. Don't mean to scare ya, but it's true.

Glad you got it fixed. To tell you the truth, my longitudinal regulating shaft is held in place by a plastic zip tie. I just remembered that about a year ago my pedal would stick and I had to tap it to release the throttle, so I put a tie rod around all that stuff at the end to keep it inserted. Do you know the specific size of that c-clip? I should stop by the hardware store and pick one up. 

P.S. That red "Stop" button on the linkage is to shut off the engine when the key doesn't.  It's never happened to me, but it has happened here on this forum.

[WrightSounds]

These cars are like steampunk, 19th century contraptions that work on vacuum, electricity, mechanics. All very Newtonian. And nothing is really hidden. It's all there to see.

Well said JasonP! I was showing my wife what had happened and what I did to correct the linkage... she said it reminded her of a Rube Goldberg machine. Pretty much!
I'm very excited about all the learning that's been going on and, yes, this forum is awesome.

Do you know the specific size of that c-clip?

I measured the diameter at the end of the longitudinal shaft with digital calipers and it measured .3 inches. The lock washer I used (with the little teeth on the inside, not outer perimeter) had an INSIDE DIAMETER of .25 inches from one little tooth across to another little tooth. I then cut a little piece, say from 5 o'clock to 7 o'clock, so I could snap it over the shaft. I think I lucked out because the thickness of the washer I used (.025") was a perfect fit for the little rut that the original clip snapped into. Here's a link to a picture of a lock washer that shows the 3 dimensions: http://www.americanfastener.com/images/techspec/345a.gif

So if the end of the longitudinal shaft looks anything like mine, get a lock washer with a dimension "A" of .25" and a dimension C of .025" and it should work.

P.S. That red "Stop" button on the linkage is to shut off the engine when the key doesn't.  It's never happened to me, but it has happened here on this forum.

That's the other thing that happened the day before the linkage prob. My wife took the car to the grocery store and called me 5 minutes later saying the heat wasn't working. Hmmm. Then she called 5 minutes later telling the car wouldn't turn off. Hmmmmmmm. I borrowed the neighbor's car and drove up there to find one of the plastic hoses had slipped out of the rubber connector piece. I plugged in back in and the car turned off. "That grey straw makes the heat work AND the car turn off?! What IS this car" said my wife. 

Needless to say it's been an interesting weekend and one which my wife wonders why we didn't buy a Toyota 

[Tony66_au]

Because buying a Toyota is akin to artistic suicide and you'd be buying beige Cardigans and shopping at LL Bean within hours of your first soulless Drive.

[ZCarFan]

seems you have discovered quite a few of the model's charms in a short period of ownership.  Don't despair however as in context of the car's age, none of these events is unusual.  The linkage problem was not the car's fault and now you know how important vacuum line maintenance is

It's amazing how much better it runs after the valve adjustment, isn't it? 

[Tony66_au]

Sounds like you are well on your way to being a W116 Enthusiast!

10/10 so far