I have a 1986 Subaru hatchback with a 1.8L it runs good but idles rough. Whole car shakes. Changed plugs. Did a compression test. 125 on cylinder 1. 130 on cylinder 3. 140 on cylinder 2 and 150 on cylinder 4. Can anyone help me out? Could it be a motor mount?

I sounds like a one cylinder isn't firing.

 

It could be a lot of things, dist cap and/or rotor button, a vacuum leak, a bad plug wire, needs valve adjustment ect.

 

What I would do is start the motor and then pull the spark plug wires off of the distributor cap one at a time.

 

*Use some rubber insulated pliers so you don't get a shock*

 

Pull one wire off and see what happens, replace it and then repeat on each cylinder

 

If you pull a plug wire off and the idle gets even rougher you know that cylinder is firing correctly, if you pull a plug wire off and it doesn't get rougher/stays about the same that is the cylinder that isn't firing.

 

I suspect you are going to find one that isn't firing.

 

Then I would swap two plug wires( make sure you keep them in correct firing order) , if the dead cylinder is now on the cylinder you swapped the wire you know its that plug wire.

 

If this works at least you know which cylinder isn't firing.

 

Most likely a bad plug or plug wire on that cylinder, but still could be dist cap/rotor, vacuum leak near that cylinder, or need a valve adjustment on that cylinder.

 

Hope this helps

Edited April 11, 201511 yr by junk250

Thanks man! Appreciate the help