2005 GT - idle surge - in cycles when AC on and occasionally when AC off but motor cold, also bucks when cold.

[dan diego]

My mustang has been a little cold blooded since I got it several years ago. When cold, it would buck a little no matter how gentle I tried to be with the clutch. Eventually I got a P0193 Fuel Rail Pressure sensor error. With the error, I noticed no additional symptoms. I cheaped out and installed the bosch replacement fuel pressure sensor. It cleared the code but I starting getting cycles of surging idle. At the time, I do not believe I was using the AC (but not certain). I returned the pressure sensor believing it to be defective but the next bosch replacement was only somewhat better. I am planning to buy the motorcraft replacement fuel pressure sensor ( 3x the cost of the cheap bosch) but thought I would take a chance on the forum to see if anyone had similar experience with a different satisfactory solution. My only mod is a cold air intake filter. At the moment, the idle surge cycles any time I turn on the AC and then other times when AC is off but motor is cold (but far less predictable than simply turning on AC).

Cheers!
Dan

 

[dan diego]

My 05 mustang GT idle surges in about 3 times when I turn on the AC or driving w/ AC on and I come to a stop.I have properly charge (~45psi) ac system. I have had the same symptoms with several different fuel pressure sensors. Any thoughts or advice?

 

[dan diego]

I solved my problem with some recommendations that I got elsewhere. I cleaned the throttle body plate with carburetor cleaner and the MAF sensor with alcohol and q-tips and viola! No more surge. Also, no more hard starts (bucking) when starting out in first gear.