1984 300TD acceleration issues different than others posts
 

Hello. Ok so the car is in park. I step on the gas, the car revs up and then without removing or moving my foot it goes right back down to idle... This happens while I still have my foot on the gas. If I step on it again, it'll rev up but eventually it'll come back down. What could be the problem? This happens while I'm driving too. The car has great pick up when I'm on the freeway though.

Digieditny

Have you checked for excessive play in your throttle linkages?

No. I just got this car on saturday and am completely new to mercedes benz and diesels... Is there a tutorial somewhere I can look at?

digi

have someone step on the throttle while you look at the linkage as it moves. odds are good you will see what is wrong if it's linkage related. likely the bolts that hold the swivel parts to the valve cover are loose.
if everything moves smoothly, and it does not look like things are broken, post back.

I'll do this tomorrow morning and get back. Do I do this with the engine running? Link to what the linkage looks like? I'll do a bit of searching.

digi

With the engine off!

Once the helper "floors" it, grab the linkage under the hood and see if you can move it more in the "go" direction.

Super-standard with a new-to-me '80s diesel MB car is to pop ALL the linkage balls loose, clean them, then lube with a drop of ATF (stone age, yes, but MB spec).

After my helper floored it, I was able to pull it in the go direction about half an inch. Would that need adjustment? If so, what exactly do I adjust?

Digi

There is a bunch of info in the Factory Service Manual about adjusting the throttle.

Available here: http://www.classictechlit.mbusa.com/MB/cstmsearch.asp?MYID=1038&SDID=1297&MDID=1168&ENID=1156&catalog_name=Retail

I recommend getting a copy, cheap too.

it could need the coupling on the pedal replaced, or the swivel on the firewall replaced.
take a picture for us.

K I will take a pic in a few minutes.

Full travel at the go pedal should result in full travel of the arm at the other extreme of the linkage the go lever on the injector pump.

Most common throttle linkage failure is the bushing on the firewall:

http://www.peachparts.com/shopforum/diesel-discussion/235493-throttle-pivot-broken.html?highlight=throttle+pivot

Here are some pictures of the linkage. How does everything look? I haven't adjusted anything. I just installed a new primary fuel filter.

Man I never noticed all the rust till I took these photos. OUCH!

digi

Oh I also wanted to say that after installing the new fuel filter, the car felt peppier but it still didn't hold power. Pushed the pedal and the rpms go up but then eventually back down without moving my foot. The car idles kinda rough. Thought it was gonna shut down on me

digi

Does the engine behave the same way if instead of pushing the accelerator, you grab the linkage near the IP and open it up all the way. If it still behaves the same way, you could probably exclude a linkage problem.

Great Idea! I will go try that right now! brb

No it doesn't. It revs and stays. Does not go back to idle. So linkage problem huh? How do I fix this? Do I just adjust one of the bolt?

Have your helper step on the pedal and signal you when the idle drops, or if there is a change on the linkage when the idle drops as you observe the linkage move around in the engine bay.

Something is probably sprung too tight maybe that's also what's causing the idle to drop. Check the spring on the linkage close to the firewall, near the oil filter housing.

I will do that tomorrow. It's dark now in the east. I will have to look at the linkage and see if there's a change. My helper won't be able to tell me if the rpms drop since I don't have a reading on my dash. Just a non-working clock ha.

digi

Then go by what you hear in the engine bay. How did you determine that the idle drops in the first place? :)

Yeah. I went by what I heard from the engine. I just hope it's visual so it'll make it a lot easier to detect the problem.

Ok I didn't see the linkage move back after my helper held the pedal down... So what else can it be? Would a clogged secondary filter be the problem? I changed the primary yesterday. Also, the car is idling a little roughly at times. Is there anything I can do about that?

I have the whole day today to work on the car. So it'll be quite interactive. Any help would be greatly appreciated!

Yes, swap out the secondary filter. Before you install it, fill it with fuel then screw it on. Check the rubber "O" rings on the banjo bolt for "rubberness". Replace if they are hard.

Do the "O" Rings come with a replacement filter or do I need to buy that separately? Ok, I'll go ahead and install the filter first before messing with anything else.

Ooof looks like your throttle bushing mount is really rusted! I just had to replace that bushing on my TD....there is a resin ball behind the mount that snugs up aganist the firewall...check to make sure this is still intact and that the mount is actually holding the bushing firm.

I bought a replacement from Phil - it was like $50

I also found out that I could fabricate a temporary one out of a big washer and a couple of flat o-rings (to dampen vibration) for about $3, but I only used that for a few days until I got the actual part in place.

Once I did the replacement, I had to adjust some of the linkages. I started at the one that links the assembly that tops the valve cover to the IP and stop lever. just lengthened them a little bit. Once I did that, I had full throttle with the pedal down.

Much better off the line acceleration.

No, your local autoZoo will have something tho. I bought a box of various sized metric "O" rings, they'll be in there.

Ok great! I'll buy a box of metric "O"s too. I'll be back. Need to drive over to pick up the filter and the "O"s. thx

If there's anything else I need to pick up, let me know. I'll check the thread on the road.

Pick up some injector cleaner, that is what I use to fill up the filter.

Any specific injection cleaner?

^ Not really, just make sure it's rated for diesel.

Ok I got everything. Going to go install. I noticed something weird with the linkages. There's a fair amount of play on it. I pulled on it for about a whole inch before it started to accelerate. I'm going to do a quick video on it so maybe one of you guys can tell me what's up.

digi

Someone mentioned the bracket on the fire wall, when your helper presses down on the throttle pedal, observe that bracket.

if you are pulling on the linkage, there is play built in for the transmission portion of the linkage. it's normal. you have to turn the accelerator rod to get the throttle to turn correctly, or step on the pedal... it's hard to do it by hand under the hood.

Ok both filters are changed now. Pretty simple. Thanks for all your help!

VSTECH. Didn't notice your post until I already shot the vid. Take a look. It's probably normal. Take a look. http://www.youtube.com/watch?v=i8hfjiZfyuk

I also uploaded a video of my radio. When I turn it on, I get loud static on the right speaker. I'm thinking the radio might be kaput!

http://www.youtube.com/watch?v=kkMJ4EmwICc

digi

Yes, they are simple, but doing it a few times will show you a trick or two, as you saw in my video.

You are pulling on the cruise control linkage, shouldn't have that much play in it.

How does the linkage on the cam cover look? Can you tell if anything is missing or broken?

I'll go take a look now. You know, after I changed the filters the car felt good. It still doesn't really move until I pedal it half way though. I didn't feel the rpms go down like they did before. I'm going to go double check now.

I have Cruise control? Where the knob in the car? Ha I didn't know that...

The bolts look fine... Does that white screw look ok?

I want to also mention that this is my first time owning a diesel car. I've read that these cars are slow so maybe there is no issue...

That screw is the Bowden cable (pressure control) adjustment. It depends, do you want each gear to stay longer in gear or not?

Third pic, behind the rusty piece that is behind the rubber block, that is the plastic bushing discussed earlier, make sure it's intact.

The cruise control is activated by the combination switch located just above the blinker stalk. It probably doesn't work.

See all those ball and socket linkages? Remove each one, clean it and lubricate with the spray of your choice.

I feel like the gears shift really good so I don't want to touch that.
Do I just peak behind the rubber block or do I need to remove it?
I'll look for the cruise control.
Ok I'll get some WD40 and clean and lubricate the linkages.

digi

The arrows point to the two bolts that hold it on. The rubber block is part of the bushing, so when you remove those two bolts, the whole thing will come out.

Remove the linkage with the rubber block, pay attention to what hooks up where, pull it and inspect. I think someone has posted a pic of it. That car looks pretty rough under hood.

Part # 123 300 13 40.

Skip the radio - listen to your engine!

Your antenna probably doesn't work and your fader switch is probably dirty and corroded. Those are things to worry about later.

Clean and lube your linkage. WD-40 will help clean, but not be a great lube for those ball/sockets. A dab of multi-purpose grease works fine.

I think there's some info on the diesel giant site (do a search, some good info/pics, but read and use with caution since there are some errors - like any Internet site).

Also look into signing up for the M-B electronic parts catalog EPC Startek, or similar.

Diesel is a whole new world. Ask first, it'll save you hassle.