Hi' I have 91 EB Falcon Auto that vibrates a lot in Drive at idle, less so in Neutral. The Vibration disappears above 20kph or if I raise the revs a bit when idling in Neutral. Otherwise its normal. Is it on the way out or is there something that can be adjusted?

have to decide if the vibration is engine or transmission sourced
Is the vibration there in neutral at the rpm of 55 mph or better Taking that at 55mph you would be in over drive and the rpm would be around the 2600 mark
hold the rpm steady and see if the vibration is apparent
raise the rpm to see if it comes in
if it does , it is an engine problem and probably a balance shaft timing out
If not then it is a transmission problem and as it would be in over drive and the indications would be a failing bearing in the rear of the transmission of transfer case

Vibration at idle brings to mind a few suspects:

transmission mount(s) broken/missing
transmission internally worn
motor mount(s) broken/missing

(1) transmission internally worn or transmission mount broken/missing - test this by shifting into neutral at the next stop light. If the vibration disappears when you disengage the transmission, then the transmission is the source of the vibration. You'll have to inspect the transmission mounts - if they're ok, then the transmission is internally worn and can no longer smoothly "slip" while idling in drive.
(2) motor mount broken/missing - also test this by shifting into neutral at the next stop light. If the vibration persists, then the transmission is exonerated, and the vibration is coming from (under) the engine. The rubber part of motor mounts commonly crack/break and or pop out and are lost.

A photo of the front motor mount for the 2003 Dodge Neon:

Try to rev the engine while at neutral if you get the same vibration to pinpoint if its from the engine or the drive shafts. If the issue occurs at a certain rev it may likely be the variable valve unit. Check if possible if you can get errors from the computer.

you should have someone put an obd2 scan tool and retrieve any engine codes first
most auto part stores will do this for you
then you can come back and give me the codes and i can help you better
if this was helpful please rate this question thank you

hi barry i have the same problem did you ever fix yours ?

Increased vibration from a vehicle indicates worn out engine supports. This vibration often disappears when revving the engine high, but is very noticeable at low revs.

You can have these inspected and possibly replaced to reduce the vibration cominf from your engine.

Hope this helps.

Check your engine and transmission mounts .

Have you tried checking the exhaust heatshields?

Hi and welcome to FixYa. Please try this:
GO out to the car, and lift up on the hood. Does it raise a bit and rattle? If so;
Open the hood, and look at the perimeter of the front radiator support. You will see 2 small rubber thingys, that look like that they are screwed onto the metal that is holding the radiator. Unscrew them a little, and close the hood. Pull up on the hood and see if the rattle goes away. If not, repeat unscrewing the rubber things until the lift disappears.

A FixYa rating (4 blue diamonds) would be greatly appreciated for my assistance.

Check the motor mounts. They might be worn or loose which can cause vibration felt when the engine is reved up or running at higher rpms than at idle.