Very Rough Idle and bumping feeling in gear....help? - PeachParts Mercedes-Benz Forum

pawoSD · #1 04-24-2006, 01:03 PM

Here's the problem, our 1983 300SD has been going downhill lately in how it runs/idles. At idle its very rough, and when put into reverse or drive it actually stutters/makes a bumping feeling at idle, almost like it wants to stall but it never quite does, unless you first start it(cold), then put it in gear, it stalls sometimes. It never used to do this. Its always run rough, but its been getting worse. We suspected injectors so we had them rebuilt at a pro-shop with the bosio nozzles, balanced and pop tested and everything....end result was more power/better acceleration but it still had/has a really rough idle. This roughness is present between 650 and 950 rpm, above that it smooths out. I set the idle around 750-800 and its still rough. I tried setting it as high as 950ish and that made most of the roughness go away in park or in gear...but thats way too high of an idle. My car idles around 650-700 and its silky smooth.

Fuel filters are new, no air in the system, the car can powerfully reach 100+ mph with no problem, the only problem is at idle.

The car does have a (potentially) old timing chain, last valve adjustment was about 12-13k ago, and they said the chain had about 3 deg's of stretch at that point. If it has stretched more since, could that cause the timing to be off?? It nails during this rough idle and makes some black/blue smoke. No smoke at non-idle rpms. Blowby is non-existant, you can loosen the cap and it does not move, and if you take it off there's nothing coming out. Starts up fine at super cold temps. When the engine is hot all you have to do is "bump" the key and its running, don't even have to glow at all. So the engine must be very healthy. We have done a blackstone report on the oil from this engine at over 3700 on the oil (rotella-t) and they said it had significantly below average wear metals, and said it appeared to be an extremely healthy engine, and that the levels of stuff in the oil would have been what you'd see on a car with 1000 less miles on the oil.

We need some suggesstions on why the idle is so bad, and what we should do. We were thinking about just dragging it to the dealer and having them do a valve adjustment + new timing chain/guides and then set the timing perfect. Think that would help? This was done on my car (by the dealer) about 2 years ago, and when I got it back with that having been done it ran wonderfully, the smoothest idle ever.

We just wanted some opinions on what might be the best solution to fix this rough idle problem. It has gotten so bad that he's stopped driving it for the most part. Sitting at lights is like getting a massage in one of those vibration chairs.

Also, the engine appears to not be able to move, its almost like its bolted to the car, should it be in that "tight"? On my car I can rock the engine if I grab it and shove, about 1" back and forth, can't do that on the '83, its in there like a rock so it probably transmits all that much more vibration to the chassis. Turning it off shakes the car pretty hard too, and yet again the engine itself doesn't move independent of the chassis, it moves "with" it, whereas mine rocks by itself and isolates that shaking from the car. Its on the correct motor mounts...maybe they are too hard? Just seems odd that it can't move...

Help?!?

pawoSD · #2 04-24-2006, 01:37 PM

We do know the mounts are less than 3 years old on this car, the previous owner had them replaced not long before we bought it from him.

Mounts still would not explain the nailing/actual noise it makes at idle. Its clackety and knocks. Also what would cause the "stumbling" when its put into gear? Seems odd...... Timing chain and guide is like $160 in parts alone!

Hatterasguy · #3 04-24-2006, 02:53 PM

My SD does this when its cold. I put it in gear soon as she catches and go, or she will stall. But if I sit in gear it will run rough and act like it wants to stall. Warm it runs fine.

Have you checked the Ip timing? Another thing you may want to do is pull the IP and have it bench tested. I bet this is a fuel related problem.

I always thought it was one or two marginal cylinders on my car but maybe not.

#4 04-24-2006, 03:24 PM

Last time mine did that, it turned out to be the rack damper adjustment. It would have an uneven idle and try to stall if it was sitting in gear when cold. Motor mounts may explain the shaking, but not the stalling.

pawoSD · #5 04-24-2006, 04:46 PM

You can hear it though, idling with no load (park or neutral) its steady and happy as ever, but as soon as you put it in drive, it makes a pounding sound and shakes/quivers the entire car, I just set the idle around 900, and it still does it, so we don't know what the issue is. If it was mounts I don't think it'd be that rough/loud....its definatley having an actual problem. I suspected timing too....we're probably just going to send it off to the dealer to be dealt with, they have a great diesel mechanic on staff, he does my valve adjustments in like 40 mins start to finish!

It does it cold or warm, the sound/feel is almost the same.

Also, the vibration/banging sound/feeling is a lot less in reverse than in drive....any idea why?

The engine has always run "harsher" than mine does, from day one, even after the new bosio injectors....I bet its a timing problem too. We'll see....

Hatterasguy · #6 04-24-2006, 05:33 PM

Dealer at $100 an hour? Man you have money.

I bet they charge you $1k to change the timing chain.

If I had to have the dealer work on my car I'd just lease a new 325, it would be cheaper.

pawoSD · #7 04-24-2006, 06:04 PM

Quote:

Originally Posted by Hatterasguy

Dealer at $100 an hour? Man you have money.

I bet they charge you $1k to change the timing chain.

If I had to have the dealer work on my car I'd just lease a new 325, it would be cheaper.

Thats just it, we don't have any $$

But we want to get it fixed and we don't know what the prob is. I can do mounts and such, but IP/chain things, no thanks.

Our dealer is reasonable, a valve adjustment is about $85-90 and gets done in under an hour + free cookies & coffee

My car hasn't been there in ages, the '83 has been the "having issues" vehicle.....

Could the thumping be a tranny issue? I am changing the pan/filter/gasket/fluid to synthetic this week on it, if there's no change I could do the tranny and engine mounts, then what if there's no change after that? What else would it be?

pawoSD · #8 04-24-2006, 06:13 PM

Some more info....

Last Tranny fluid change on the car was exactly 15,000 miles ago

Last Valve adjustment was one year or about 13,000 miles ago

Chain has "1% stretch" (or one degree) according to the MB diesel tech that last did the valve adjustment at the dealer

Tranny mount: Probably original

Engine mounts: Three or more years old

Injectors: Just had bosio nozzles put in and full balance/pop testing procedure

Fuel tank always has a vacuum in it, goes "whoosh" when opened, however, running with the cap off the tank changes nothing.

Filters are brand new, engine makes good power as high as 5k rpm!

Some smoke at idle. (not a lot)

From this....what would it most likely be? I'll see if tranny fluid changes anything, and then I could do the mounts. Those would be alternatives before a dealer visit, but it needs a valve adjustment anyways, and he could probably tell us specifically whats the issue.

tram · #9 04-24-2006, 06:30 PM

Quote:

Originally Posted by pawoSD

You can hear it though, idling with no load (park or neutral) its steady and happy as ever, but as soon as you put it in drive, it makes a pounding sound and shakes/quivers the entire car, I just set the idle around 900, and it still does it, so we don't know what the issue is. If it was mounts I don't think it'd be that rough/loud....its definatley having an actual problem. I suspected timing too....we're probably just going to send it off to the dealer to be dealt with, they have a great diesel mechanic on staff, he does my valve adjustments in like 40 mins start to finish!

It does it cold or warm, the sound/feel is almost the same.

Also, the vibration/banging sound/feeling is a lot less in reverse than in drive....any idea why?

The engine has always run "harsher" than mine does, from day one, even after the new bosio injectors....I bet its a timing problem too. We'll see....

The issue that I bolded for you right there DOES sound like a defective motor mount. It loads the defective mount and transfers all the vibration/ noise right into the cabin.
I forget which motor mount is loaded in D rather than R, but the driver's side mount can perish from a diesel leak, and the passenger side can go south if the turbo or anything else drips oil on it.
The fact that you can't "shake" the engine tells me that the rubber in the mounts is gone, and the heavy engine is sitting metal to metal. You can't "bounce" metal.

That would be where I would start, then look at valve adjustment. Basic stuff first.

pawoSD · #10 04-24-2006, 07:50 PM

I've been thinking the same thing, I recommended to him that we begin with changing both engine mounts + the tranny mount to see if it makes it go away, if it does then problem solved, if not...then on to a valve adjustment.

It still seems like the engine is "skipping" or "loping" when its in drive though, there's a rhythmic pulse in the idle when its in gear (drive) thats not there at all in idle....oh well, I'll do the mounts then see how it is. All the mounts can be replaced for 2/3 the cost of a single hour of Dealer time, so thats the best route to go for now.

Hatterasguy · #11 04-24-2006, 09:59 PM

I'd also borrow/rent the RIV tool and see what the IP timing is. Checking the crank to cam timing is easy as well.

Can you use the RIV tool on the 617 or do you have to use that horrible drip method?