2008 MKX Idle Issue

[Cyclonebill]

A couple of years ago, I replaced the brake booster on our 2007 MKX. At the same time I replaced coils and plugs. I removed the intake to facilitate an easier install of all elements. I purchased the coil/plug kit from Tasca and received new intake gaskets which I installed when putting everything back together. The car has 200,000 plus miles on it, but ran fine prior to booster failure. Now I can start the car and let it warm up. When it reaches a temperature that would initiate the cooling fan, it starts a rough idle. Sounds like, chug, chug, chug, chug...Starting vehicle is normal, initially idles up, then settles down to the 6-700 rpm range and idles smoothly, then as the temp reaches that critical point it begins to get rough, lowers to the 4-500 range and may actually die. If I restart, it's in the "chugging" mode and every so often I will have to tap the accelerator to keep it from dying. Since this happened, I have replaced the MAS, the purge valve and the PCV valve. We would like to sell the car, and outside of this issue, it's a pretty nice car. Any suggestions or similar experiences?

[1004ron]

I would start by reading the stored error codes using Forscan or other device that's know to have the capabilities with Ford.

 

After that I'd use the scanner monitor the O2 sensors paying particular attention to when the engine is warmed and the A/F ratio switches from Open Loop to Closed Loop.

[DILLARD000]

5 hours ago, Cyclonebill said:

...couple of years ago, I replaced the brake booster on our 2007 MKX...replaced coils and plugs

...removed the intake to facilitate an easier install...coil/plug kit from Tasca...new intake gaskets

...200,000 plus miles...ran fine prior to booster failure. Now I can start the car and let it warm up

...reaches a temperature that would initiate the cooling fan, it starts a rough idle...chug, chug

...Starting vehicle is normal...idles up...settles down to the 6-700 rpm...idles smoothly

...as the temp reaches that critical point it begins to get rough, lowers to the 4-500 range and may actually die

...If I restart, it's in the "chugging" mode...have to tap the accelerator to keep it from dying

...Since...replaced the MAS, the purge valve and the PCV valve

...would like to sell...outside of this issue, it's a pretty nice car

Starting the Engine cold, do the RadiatorFans switch on when you switch the AC on?

If they do NOT, then the FanControlModule\FCM on the upper left corner of the RadiatorShroud has likely failed.

In my 2008 V6~3.5L~DOHC Edge, a couple of years ago had the FCM intermittently short out the control signal wire from the PCM,

when this happened, the engine would sometimes momentarily dip in RPMs+Power then come back up,

other times it would completely stall+die & need to be restarted, then it would run normally untill randomly it would die again.

No TroubleCodes were set, so it took me several months to figure out cause.

If you do replace FCM, be sure to get OEM Ford part, aftermarket FCMs, though cheaper, are notorious failure items ( I learned this the hard way).