Car cutting out stepper motor/ rectifier?

[Mustang]

The battery on my car was quite week and the recent cold snap killed it off completely. After jump starting it every time it was left for a few days I finally bit the bullet and bought a new battery. I fitted the battery last Tuesday. Everything seemed fine voltmeter showing 14v with engine running. I've noticed once or twice that the car seemed to 'hesitate' a bit on the cold start. It also seems to be idling lower (I think) than before ~500rpm . Anyway, twice now, the car has stalled when I was slowing down approaching a roundabout. So something is wrong.
My initial thought was stepper motor, but I seem to recall that jump starting can fry the rectifier? Any thoughts?

[Gerry]

Hi mate,
Ive had this issue after removing battery ftom my GPX, battery was out for a few days,
I installed battery and had the same problem youve described, i didnt touch anything.
I drove the car for a few days and problem went away.

[CJ]

Mustang, pull the negative feed with the engine idling and see if it dies, if so its the alternator. Its not beyond the realms of possibility that the stepper has given up the ghost at the same time....

CJ

[paul2508]

happened to me couple months back when i removed the battery and replaced it .when i put the new one in it was running on low revs and cutting out on me.took the stepper out ,cleaned it and all was good. laura mentioned that it happened to her too in a thread i put up. try cleaning the stepper to see if there is any difference

[CJ]

If find that letting the car idle for 10 mins with the a/c intermittently on/off after the power has been disconnected is sometimes required so as the ECU can learn the correct idle speed, been discussed before IIRC.

CJ

[Gerry]

I really dont think this is stepper motor related,
the common factor here in all the cases is that the battery has been disconnected.
I do think the ecu needs time to re-adjust itself after a period where the battery has been disconnected.
In cases where people removed stepper and cleaned it, i think the ecu has re-adjusted itself by then to make people think
that cleaning the stepper has fixed there problem.

But i could be wrong and im open to correction.

[Mustang]

Mustang, pull the negative feed with the engine idling

I did that and the car continued to run ok. Under normal driving the voltmeter is reporting a steady 14v.

The car is ok on cold start as the normal 'high idle' is plenty to keep it running, but once the car has warmed up, it'l cut out if the throttle is not applied. The revs will dip to ~250rpm, and either cut out, or bounce back to ~500rpm, where it seems to idle steadily enough without hunting. I didn't have the time or the light last night to go at the stepper motor.
I guess it looks like a stepper motor issue. Is the rectifier associated with the alternator, if so can I rule that out?

[CJ]

Is the rectifier associated with the alternator, if so can I rule that out?

Yes and Yes. If the problem goes away, its could be the 'learning issue' Normally, stepper issues manifest @ cold start (but not always so in my experience). Let the car idle for 15 mins with the a/c on for 5 minutes in the middle, if no joy, off to Camskill with ya! An auld diagnostic might be worth a try if all else fails...

CJ

[mivecmad27]

i had this prob with an fto recently(not my own fortunately),it wouldnt idle when warm,turned out the vacuum pipe to the map sensor was slightly kinked,fitted it properly and she ran sweet

[optical illusion]

happened to me couple months back when i removed the battery and replaced it .when i put the new one in it was running on low revs and cutting out on me.took the stepper out ,cleaned it and all was good. laura mentioned that it happened to her too in a thread i put up. try cleaning the stepper to see if there is any difference

Yep, same thing happened me the day after I replaced the battery. Cleaned the stepper - good to go!

[Mustang]

If find that letting the car idle for 10 mins with the a/c intermittently on/off after the power has been disconnected is sometimes required so as the ECU can learn the correct idle speed, been discussed before IIRC.

CJ

The car seems to have righted itself, I left it idle for all of about 2 minutes the other day when I got home from work. Seems to be running fine now. Just as well, too cold and wet out to be messing with stepper motor etc.