So this '84 300D with 144k on it has recently developed a very noticeable vibration at 1000 rpm. Both fuel filters are new, tank strainer, and all rubber fuel lines and return lines. Valves are adjusted correctly. New rack limiter bolt. None if the injectors are leaking, and neither is the injection pump. The plastic primer was replaced with a metal Monarch primer. I'm at a loss as to what the cause is and where to begin troubleshooting. The car idles smoothly, and accelerates nicely and has no problems achieving 85 mph on the highway.

Engine ,trans Mounts or anything on the driveshaft including torq. converter..Get it to a mechanic ,while under the car have them show you what theyve found ,then bring up how much time to do the job ,all this to get your estimate. I bought a car that had a noticable vibration coming under the hood ,the seller didnt realize the hood was vibrating on the fender and a simple rubber hood dampner was required to keep the hood from metal to metal contact.

Similar to the above, mine had a bone-rattling vibration that shook the whole car. Turned out to be the @$%& air cleaner (that was the last straw on that dumb thing).

These engines vibrate, so anything loose anywhere on the car will become a manifestation of that.

-Rog

Until you fix the problem. The air cleaner used to break the rubber mounts. Then, in the process of stopping engine leaks, the manifold came off for a new gasket. While thee, I secured the drain tube, installed a new o-ring where the housing goes into the tube and installed new rubber mounts in a way that they are not under constant tension. No more breaking. No engine leaks either. Only cost time & Elring gasket set.

OP, be absolutely certain that your drive shaft flex disks and center bearing with carrier are good. I'd change them unless you KNOW that they are good. It's a great bet that the PO hasn't changed them. I wouldn't drive it until those were checked. You really wouldn't like the result. Use good parts. I think the disks can be Lemforder. The carrier can't.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Actually, I just recently installed new engine mounts, transmission mount, guibos, and the center support bearing, as well as rear axles. But this vibration doesn't occur while driving, only while parked. I've also replaced all three air cleaner isolation mounts, but did just notice the air cleaner shaking wildly at idle, and found one of those mounts was broken. I think that one will get a machine screw and a few nuts.

Be sure the drain tube that the air cleaner fits into is mounted solidly. Be sure the rubber mounts aren't under stress.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Well when the Car is not moving 1000 rpms is too fast for an idle speed. Is that when the Air Conditioning is on or off?

If you are using 1000 rpms for you idles speed why are you doing that?

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84 300D, 82 Volvo 244Gl Diesel

It can be concluded, from actually reading the OP's words, that at idle below 1000, the engine is smooth, and only when engine speed is raised to 1000 does the vibration appear.

I would still like to here from the OP if he or she wants to answer.

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84 300D, 82 Volvo 244Gl Diesel