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post #1 of 8 (permalink) Old 06-04-2017 Thread Starter
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I have a '97 mustang GT starts and will drive if I keep the rpms up, while idling it'll die, any ideas?
Cleaned the IAC valve and the MAF sensor.
Spark plugs is next on my list of things to do cuz they're over four years old
Also could it be the air filter it has a K&N intake that's black when it should be red, it's old too.

I bought this car mid 2014 drove it a few months and sold it to my brother in law, he's not one for taking care of his cars that's why there's a lack of maintenance.

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post #2 of 8 (permalink) Old 06-04-2017
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Vacuum leak possibly, hole in a line or line disconnected somewhere.

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post #3 of 8 (permalink) Old 06-04-2017 Thread Starter
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I was kinda thinking a vacuum leak as well, where should I start to check that?
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post #4 of 8 (permalink) Old 06-05-2017
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Could also be in the charging system (I had an alternator that was failing on a car years back, that acted like that). I had to keep it in neutral to keep the RPM's up for a day or two (at stop lights), till I got the replacement alternator in.
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post #5 of 8 (permalink) Old 06-05-2017
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Get a can of carb cleaner and start spraying it around hoses and intake gaskets while keep the rpms up. If the engie surges you know where the leak is.

This has vacuum leak written all over it.

Any CELs? Possibly a lean code?

Matthew 26:52-54 / Go Pack Go!

1987 Mustang GT Hatchback - 2V Mod Swap In The Works

1997 Lincoln Town Car, PI Intake/Cams, Sofa-On-Wheels, "Fat Tony" we call it

2001 GT Convertible - D1SC / Geared / Cammed / 440wh 400wt - TOTALED 2/2019
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post #6 of 8 (permalink) Old 06-05-2017
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For low idle concerns there are several "possible" causes.

If this were my car I would start with a review of the battery and charging system.

Do the dash gauge needles do a full sweep at initial key on? If so, for a Ford this proves power was lost and the PCM memory was also lost. Are the PCM readiness tests complete?

Don't cut corners here as this problem could be battery related.

Howto perform charging system voltage drop test:
https://www.stangnet.com/mustang-for...-drop-test.56/

This could be a vacuum leak. But not just any vacuum leak as it's likely to be between the MAF and the IAC. Such that it will make the MAF report low air flow.

Or the IAC itself could be totally ineffective/bad.

This could also be a MAF problem. Or low fuel pressure.

It would help the trouble shooting to know:
  • IAC duty percent
  • MAF air flow
  • RPM's
  • system voltage
  • computed engine load

Here some information on how to get an affordable ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-for...-drop-test.56/

Here's some information on how to trouble shoot IAC/Idle issues:
Ford Mustang Forum - View Single Post - Is your mustang stumbling, dieing at idle or idling rough?

Here's some information on how to trace Parasitic battery Drains.

The Trainer #26: Using Voltage Drop To Find Key-off Battery Drains


The BEST Way TO Perform a Parasitic Draw Test

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.

Last edited by wmburns; 06-06-2017 at 10:12 AM.
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post #7 of 8 (permalink) Old 06-05-2017 Thread Starter
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No check engine lights, used some throttle body cleaner to spray the hose areas and rpms didn't change, tested alternator was a volt meter and it was 12.6 off and 14 running.
Though I am having to disconnect the battery cables in between drives or after an hour the battery will die
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post #8 of 8 (permalink) Old 06-08-2017
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The alternator results are not complete. A simple volt test does not check for bad diodes or weak connections. For best results perform the voltage drop test with all loads on as described in the link. In addition actually have the alternator and tested at your local auto parts stores. There's more information in the links provided.

If you are certain there are no vacuum leaks the next thing to check is fuel pressure. Is the intake vacuum reference line to the fuel pressure regulator connected and leak free? What is the fuel pressure.

It's also possible to have a vacuum leak in a spot that you can not see. The ODB2 scanner can help with that by graphing MAF flow compared to Long term fuel trims (LTFT). A vacuum leak often shows up as high LTFT at idle the decrease as RPM's go up.

A low tech way to trouble shoot is to pull and plug the EVAP line. Does this improve the situation? IF so the the leak is in the EVAP system.

Note, added information on how to track down battery drains. Please review all of the information. Yes it can be very hard to track down. However it could be something simple like a bad ignition switch, radio, or alternator.

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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