I have purchased a 2006 Mustang GT Convertible - When I first got it about 8 months ago I found after it was warmed up and put into reverse (Automatic) with foot on the brake the engine occasionally just starts to stumble like it is running on 4 cylinders , At that time it had a code for a crankshaft sensor so I replaced that as well as both Camshaft sensors and coil packs , still did it - then I saw a post on a website that this car has an issue burning up a diode in the alternator which causes it to stumble under electrical load (reverse and brake lights) and throw the phantom code . I replaced the Alternator with a new high output unit along with a new Battery and a new 4 gauge line from the alternator to the battery .... took it out today and still doing the "miss" stumbling but no longer throws a CEL code . Only happens at idle usually when backing but also did it today waiting at a stop sign . I am baffled and looking for any advice or ideas on what to try next ! Side note the car has never stalled and if I throw it in Neutral and rev it up the stumble goes away .


Thank you in advance for any and all help

 

How many miles are on this vehicle and the last time the spark plugs were changed? Could also very well be a dirty MAF sensor, throttle body, or fuel filter.. IIRC these usually don't throw CEL codes that I'm aware of.. Meanwhile, if any of the info provided may apply to your idle/stumbling issues? I would highly suggest checking each one of them.. That being said, welcome aboard.

 

Ditto on the dirty MAF sensor, dirty throttle body and plugs. WHen I had my 2006, she had those symptoms at 85,000 miles. Fresh plugs and a MAF sensor/throttle body cleanup resolved the issue, and she ran smooth as silk until I sold her with 201,000 miles.