Sounds like you ave a misfire. Could be as simple as needing a tune-up.
There are a few reasons why a car shakes when idling at a red light. Some reasons could be the ignition coil, motor mounts, or spark plug problems.
The car needs a tune-up, or the motor mount(s) are bad.
You have a tire out of balance. Have all 4 tires balanced and rotated. If it still shakes have the motor mounts inspected.
water in the fuel can cause an idling motor to sputter and/or die.
Rough idling is whenever the vehicle's motor "misses" or does not fire causing an imbalance and a loss of rotation reducing the motor's power and causing excessive shaking.
There could be several reasons why your car is idling hard when the air is on. There could be something restricting air flow to the motor. A mechanic could diagnosis the problem for you.
Could be in need of a basic tune up.
check the engine mounts
I would like to change the blower motor in my 1994 Ford Tempo by myself. Do you have any instructions for me to follow?
A car can shake because of a problem in the transmission although this usually is not the problem. I will assume it shakes while it is idling or just starting out. It can also shake due to broken motor or transmission mount(s), bad u joints, a loose harmonic balancer, an unbalanced driveshaft or problems in the rear differential.
with a motor dolley
Motor is idling rough.