93 Magna exec (think this is same as the Gallant) The revs drop off when stationary only when car is warm.

You need to get yourself a repair manual for your car, you can buy one at any parts store for around $20.00. And it will give you ideas on what to check, I like Haynes the best for manuals. If the timing belt or chain I am not sure what they are in newer cars. The car recently they drop off when the car has reached right temperature.You say the revs drop off when car is stationary.That sounds like a timing chain to me. But yet that manual would give you other ideas to check. It might be the computer, a bad sensor someplace well heck that is the problem it could be anything. So try the timing belt or chain; get that manual and check things out for yourself. Or else take it well pull it to a shop; they will get to the bottom of things for you. I wish I could be more help to you, hope this helps and good luck!


Regards,
VOTIT

If it would be timing chain that jump you would have low rev and no power check for block air filter and clean throttle body with a can of air intake cleaner that stuff dont damaged oxygen sensor and catalytic convertor make sure you clean idle air control (IAC) hope its a fix let me know pierre

Depend on The Year of the Vehicle.
But the common problem is The IAC. Idle Air Control Motor.
The motor is used to ADJUST the IDLE.
But some times come defective.
and other times Just the Idle come Inadjustable. when is there
any VACCUM Leak. Pluged PCV.
Missfiring etc.
Check the Distributor CAP If is Aplicable.
Dist. ROTOR.
WIRES, Spark plug, Fuel filter. Air Filter.
Check the hose from the AIR HOUSING assemble to the throttle Body. for any Cracked or pinched on any place.
Check the TIMING. if is adjustable. Adjust as need.

Ok.. I hope this help to try diagnostic your Vehicle.

GUILL

If it is an automatic trans this can happen because of a faulty throttle position sensor. If it is manual it is just faulty transmission.