I have an automatic 2006 Mustang GT Premium Convertible, it just hit 80,000 miles this week and it has nothing performance done to it.

I just changed my alternator for the second time in a year. Except now after changing my car is dying on me when I come to a stop or am driving low speeds like 5-7 MPH. If I'm just idling with my foot on the brake the idle is low around 600 rpm. If in neutral or park it'll go back up to the 750 or so it should be at.

Going to work in the morning as I come to a light the rpms will just drop, car shuts off no warning and the battery light and i THINK the check engine light come on. Turn ignition off, turn back on and pretty much no problem unless it happens again.

I thought this was only happening in the mornings when the car was cold but I was just driving around for a half hour and I was driving really slow through a packed parking lot and it happened five times in a row in 2 minutes.

There is no CEL, I had advance auto check my alternator and battery they said both check out no problems.

I don't even know what to check now but my car can't keep dying on me. Did I damage a sensor or something? What can I check, what info do you need to help diagnose it?

Thank you!

 

i would try disconnecting the battery for a half hour or so, and then reconnect it and see if that fixes it. otherwise if the alternator passes you may have a throttle body issue, pull the air inlet off and clean the throttle body and retest. good luck

 

And always clean the battery connectors with a terminal brush.Even if you can't see it, they get a thin film of corrosion that should be cleaned off each time a connector is removed. The battery post should be cleaned as well, even on a new battery.

 

Oh I forgot the car will sometimes lurch forward quite hard like I gave the throttle a quick stab. This happens as I'm coming to the complete stop.

 

The throttle body looked clean, no real gunk - maybe a small film residue of oil. I looked into the intake manifold and saw some oil in there.

How would I clean the TB? Pull it off spray it down? Can I leave it on?

Could maybe a sensor be messed up? It sometimes hunts for idle a few seconds after getting turned on in the morning.

Thanks for all your help fellas, this is just getting dangerous now and I dont have another car.

 

some throttle body cleaner in a spray can works well, if that doesnt fix the issue, you may have a bad TB sometimes they dont set codes and can be a bit hard to diagnose

 

would there be a way to test to voltage like on any other sensor?

 

there are actually 2 sensors in the TB plus the circuits that run the motor, there is a way, but the wiring is likely not the issue. and if the fault is intermittent, testing will be tricky as it may not show bad when you are looking. generally if the wiring was at fault it will do 2 things, short to power or ground, or go open. if any of the circuits do this the pcm will pick up on it and set a code. since you have no codes there is a high probability that the wiring is good.

 

An idle of 600 rpm when the car is warmed up, in gear, and you have your foot on the brake is normal. So is 750 rpm in Park or Neutral when the car is warmed up. As to the problem areas, I can't help you.