I've got a 1997 Lincoln Town Car, Cartier Series.
I notice that when idling in the Drive Gear, the car sometimes
surges ahead, occasionally with force a bit stronger than
the force with which I've got the brakes holding it back.
And sometimes, the engine dips really low, almost to the
point where it seems like it's going to stall, which
thankfully it doesn't.
One other pattern: the car only does this when I've got
the heater or A/C on.
What could this be and how might I repair it? I took it to
Midas and they adjusted the idle, which helped but didn't
ultimately solve the problem.