a sometimes shake condition
 

car in question is an 84 300sd. last week or so i have experienced quite a bit of engine shaking at idle. natural to assume that i must replace the engine mounts. my question - this is an intermittant shake condition. does it sometimes. then other times no shake. this be engine mounts even though the shake is a sometimes affair? thank you.

There is a good chance this is being caused by the rack dampener bolt on the back of your IP. The original bolt used on these cars had a weak spring which wears out over time and can cause a rough, irregular idle. If your records don't indicate you have ever had the upgraded version put in, then get one and put it in. They cost about $40. Procedures for adjustment and installation abound on this forum if you do a search for rack dampener bolt.

Also think about fuel filters, air filter, condition/quality of fuel, valve adjustment, injector clogging etc. Maybe a high speed tuneup is in order. :D
But if your idle is irregular and shaking only sometimes, chances are it is your rack dampener bolt.

The engine mounts are not the cause of the shake. If intermittent, it can be the rack dampener bolt, or it can be an injector that is partially clogged.

However, if the engine mounts are original, they will have a pronounced effect on the shake. With new engine mounts, the amount of the shake is greatly reduced, no matter what the cause.

So, don't dismiss engine mounts out of hand, just because the problem is intermittent. It won't solve the problem, but new ones can lessen the symptoms.

I also have it happen, the hotter it is outside and the hotter the engine is running the worse it is. If its normal temps outside and I am doing normal driving it won't do it at all....I'll just change out my rack damper bolt the next time I find myself at the stealership parts dept....:D I know this is the culprit because when adjusting it with the engine very hot and idling/shaking I can minimize the shake adjusting the bolt but cannot completely get rid of it.

On the topic of the rack dampener bolt, I got an upgraded one, have replaced engine mounts AND engine shocks ($$$) AND engine shock mounts (once again $$$). All this helped, but I still have a steady up and down shake of my engine. My idle is consistent. If I turn the bolt way in, this smooths out to nothing but then of course I have the problem of the engine dipping to super low RPM's after acceleration then letting off pedal.

Is this the natural vibration of a diesel engine? It's not my front shocks, they seem decent enough. It is not an absurd amount of shaking, just a steady movement of the car (83 300cdt) on a vertical plane. My injectors are all good, were replaced about 4 months ago w/ rebuilt bosch, my valves are adjusted, etc, etc. The car runs great. I'm just not sure if it is irregular or not.

hopping
 

a five cylinder does hop up and down. if you arent used to it it seems like it can t be right but it is. if not sure check out a known well running car with an experienced five person.

also the person with the intermittant shake sounds like a fuel problem of some kind. i have noticed that when my car is about to run out of fuel it will shake a little. perhaps you are losing prime. perhaps the prime pump?

Is this at idle?
If you put it in Drive, stopped, with brake on, does it still vibrate?
If you put it in reverse, stopped, with the brake on, does it still vibrate?
If it does not vibrate in one direction, but the other one does, it's a motor mount.

Did u also replace the rear engine mount/ tranny mount ? It does help.