Shakes when idling - 2002 Chrysler PT Cruiser

Look for a vacuum leak.

A shake usually means a cylinder miss.
Is the check engine light on ?

What about new spark plugs and wires?

my 2000 camry also shakes when idling. Looks like the radiator fan is culprit, but havent had time to change out yet. looks like old blades on fan broke off making it unbalanced when spinning to cool off causing excessive shaking. When driving its cool enough where that particular fan motor does not need to spin, therefore no shaking. possible solution is replace the fan that is wobbling.

Check engine and transmission mounts.

old engine mounts can cause that problem, even if they look ok sometimes

your idle is set too low to fix this there should be a screw on the throtle control if you need help call me at 352-742-0878 or email at [email protected]

Shakes how? While stopping? Or solely while idle, Engine light on?

If if shakes while stopping you need to check you're wheel hubs and or Suspension ,

Shakes at a light, You may have a bad fuel Injector, Check you're psi in you're fuel pump, A TPS would cause low idle or sometimes high idle, With low idle and a bad motor mount it would shake,

I know theres a few things I'm missing but,.. I have a major Headache atm so I'll get back to you with some more, when i can think better. :)

Suggestion only! If you had no shake before the tranny work,then retracing the steps backwards is a good way to find the new problem.
Go back to the tranny shop and complain #2 go to another tranny shop and get a professional to look at their work.

This can be your Idle control valve, when you turn the air on it puts the engine under load and your computer will increase the idle automatically to prevent the engine from cutting out.
When you are standing still and the car is shaking, by touching the accelerator very softly does the shaking stop? If so check the idle control valve.
I hope this will help.
Regards
Sam