2006 Ford Fusion 4 cylinder. When idling in gear at stop lights, engine keeps revving up and down between 200 RPM and 1500 RPM and on many occasions stalls right out. Happens when engine is well warmed up. Dealer has not solved problem which is annoying/dangerous in city traffic.Dealer has said it may be related to air condition.

the rpm limiter will pull back the rpm to limp mode
select low range 1st gear or if automatic select manual 1st gear That will allow higher rpm at low speed

a number of possible solutions, including a vacuum leak (check hoses, use a spray throttle body cleaner o9n the intakie manifold looking for leaks), or the Idle air controller is dirty or defective, or the throttle position sensor is bad. Do you have a check engine light?

Does it sound like Metal on metal noise? or like a knocking noise?

If it increases with RPM that means you may have a serious issue.

If your comfortable i'd take off one coil pack at a time and see if the knocking stops. If it stops that cylinder might have Rod Knock..

it could be valve lash, or a valve train tick as well. There are several different things sadly.

please say you did not get the engine steam cleaned...as you can cost yourself a LOT of money.hopefully the heat will dry things out, otherwise get the car put on a diagnostics machine.

last one or i will not get up for work tomorrow,its the thrust bearing ,**** plastic fittings used ,when it goes completely ,just renew the whole lot ,if you drop subframe then they are easy to change ,about 2 hrs, but you mush drop the subframe ,its only 4 bolts two either side

jtg

This generally indicates a vaccumn leak, or sticking idle air control valve.

the idle air control solenoid or a vacuum leak on backside of intake the hose that goes to pcv valve.they are both common problems on this car.check for vacuum leak firstthanks for your question....