Smooth idle in Park--hard shake in Reverse
 

When the engine is cold and is started the idle is smooth.
With a foot on the brake and it is then shifted into Reverse or Drive
there is a hard shaking. After the engine warms up the shaking goes away.
The ambient temp is in the low 50's.

What's going on?

Thanks,
Jeff

Many things perhaps or maybe the idle is just set a little low. So when the engine is put under load the idle speed is forced down too far. Contributing to this is when the engine oil is cold there is a lot of aditional drag on the engine to start with.

Then there is the aspect of running on the wvo. When the system is cold it could contribute to the issue. Much thicker viscosity to the fuel for starters. It in my opinion takes quite awhile to clear all the vegatable oil from the system before shutdown on a two tank system.

passenger's side motor mount collapsed possibly?

I've seen the same issues with a bad transmission mount.

fuel filter
 

My son and I replaced the main fuel filter and that seems to have solved the problem.
He now drives this car to school and so I haven't been in it enough
to monitor how it's running. Teaching him to listen closely to strange sounds.
and have an antenna up for strange vibrations.


I still don't understand why it was smooth in Park and then started bucking
when put into gear but we will check all the mounts.

Thanks,
Jeff

When the car is in neutral or part there is less load on the engine because the transmission is just freewheeling. Once you put it in gear the trans puts a load on the engine trying to move the car forward or reverse, and you are actually holding it back with the brakes. The RPM will often drop slightly when you put it in gear as well.

It's kind of like a guy standing relaxed, versus a guy waiting for the starting gun at a race. Neither are moving but the runner's legs are all tensed up waiting to take off while the relaxed guy's legs are holding him up but with no immediate readiness to take off.