Low idle

Tiny
MSMCCORKLE
  • MEMBER
  • 1997 FORD MUSTANG
  • 4.6L
  • V8
  • RWD
  • AUTOMATIC
  • 119,000 MILES
I tried starting my car (GT model) and it would not turn over. I disconnected the positive cable and checked it with a multi-meter and it read 12.8v. I let it sit for a few minutes and tried again and it struggled but started. When it started, it was not as thunderous as usual. (I have straight pipes). When it started up, it felt different so I checked the rpm. I was sitting around 500 rpm. It usually idles around 2000-2500. I have no idea what is going on.
Help!
Mack
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Thursday, April 13th, 2017 AT 1:52 PM

4 Replies

Tiny
STEVE W.
  • EXPERT
500 rpm is a bit low, that engine should idle around 650-700 rpm once warmed up, around 1000 when cold and it drops pretty fast as it warms up.

When was the last time the engine was serviced? The no crank sounds like dirty connections. Go over those and clean them at both ends. A fuel pressure test would be a good thing. If the converters were removed that isn't going to help the engine as it monitors them to determine how to map the fuel and spark.
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Thursday, April 13th, 2017 AT 2:08 PM
Tiny
MSMCCORKLE
  • MEMBER
It was serviced about two months ago just for a check up. I also had the oil changed about the same time. The positive connector was a little dirty and I cleaned it off. How do I go about a fuel pressure test? It ran just fine yesterday and earlier today. Just the last time I started it this afternoon was when it started. Is that usually how something like this happens? Just starts doing it all of a sudden?
Also, thank you for the quick reply.
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Thursday, April 13th, 2017 AT 2:14 PM
Tiny
MSMCCORKLE
  • MEMBER
I just started my car again, and the idle was correct at around 1000. Any reason why this would suddenly start working again like it should?
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Thursday, April 13th, 2017 AT 3:12 PM
Tiny
STEVE W.
  • EXPERT
Loose or dirty wiring connection would be the most likely reason if it "fixed" itself. The issue is finding it when it is an intermittent problem. You mention cleaning the positive connector. If you removed it to clean it, that could have reset the ECM so it now idles correctly. I would clean every connector by opening it, spraying some contact cleaner and re-seating it, look for corrosion or loose pins. Then wait and see if it does it again.

And that is how some issues occur, you turn the key and the battery voltage hits a marginal connection or component and it stops functioning. Other issues are simply caused by wear and time.
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Friday, April 14th, 2017 AT 6:32 AM

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