Problems at idle to 1k rpm, what next? - Mustang Evolution

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Old 05-24-2016, 10:44 PM   #1
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Problems at idle to 1k rpm, what next?

I'm running out of ideas here. 2002 gt and an auto. at start up rpm surges up and down pretty severely. Driving around 1k rpm and the engine bucks, feel like the tranny isn't helping any. Over 1kish rpm and it runs smooth. No codes being thrown. And its erratic, sometimes it runs just fine at 1k. It did runbadly more often if i turned on the headlights, so seemed like that was a factor.


What I've done so far:

I've replaced lines that might have a vacum leak, no real change.

Replaced pcv valves, no real change.

Cleaned and then replaced maf, no real change.

Cleaned then replaced egr, no real change.

Cleaned then replaced iac with regular parts place, big change. Stalled like crazy. Replaced with new motorcraft, so far no stalling but back to the original issues.

After doing all that it seems that the headlight has less to no affect, it might be slightly better but its not fixed obviously.

Ideas?
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Old 05-25-2016, 11:41 AM   #2
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The charging system may possibly be weak, causing driveability problems. You should have the battery/alternator tested.
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Old 05-25-2016, 02:56 PM   #3
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I agree alternator check would be good. A failing one can cause a ton of issues.

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---------- Post added at 02:56 PM ---------- Previous post was at 02:56 PM ----------

How about the TPS?

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Old 05-25-2016, 02:57 PM   #4
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When my IAC was bad or not right (part store brand non Motorcraft) when i would turn on the lights, windows etc, it would make the idle dip too and would rev up and then go a little erratic.

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Old 05-26-2016, 12:58 PM   #5
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Battery is less than a year old, but I'll get the charging system tested. Voltage is good, but it might be weak in the amps area I guess. If it's bad it will be a few weeks before I can swap it, all my tools are on the wrong side of the country right now.

I haven't touched the tps yet. If I swap it I'll have run the gamut of the common issues I guess.

On the upside I've put a few miles on since the motorcraft iac went on and no stalling yet. I was making every turn with a dead engine with the parts store brand, my starter was getting quite the workout.

Is there a vacuum line running the the tranny on these cars? My older rides all used vacuum to control the shifts, not sure if these are computer only or not. No jack here, so I can only get to stuff from the top until I get back to my gear.

I've got an intercooled SC sitting in my garage right now, waiting to get my day to day issue solved before I start the install on it. That's driving me a little batty
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Old 05-26-2016, 02:20 PM   #6
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I have a manual transmission, but I don't think that the electronic shift transmissions use a vacuum solenoid any longer... I know that the E4OD transmission in my 24 year old truck doesn't use any vacuum.

Also, whenever you change anything electrical, like sensors or the IAC valve, you should disconnect the negative battery cable for fifteen minutes or so. That will allow the PCM to erase it's memory, and it will relearn the the new idle trim much faster than if you leave the battery connected, and let the computer relearn it over many drive cycles.

The symptom of the idle being affected by the headlights, creating a load on the charging system, is what makes me suspect that your charging system may not be working properly.
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Old 05-27-2016, 10:13 PM   #7
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May be on to something here. I fired up torque and set a voltage gauge. The dash gauge showed normal but torque was reporting mid-high 13, fairly erratic. Voltage wise, very low "normal" at best. So into the garage and grabbed my meter to check across the battery. It was a smidge higher but still not the 14+ i wanted to see.

So on with everything. Voltage gets seriously erratic. dropping into the 12s and not rebounding at all. Easing the throttle up and stumble stumble. Still no cel, dash gauge is steady normal, awesome. Raise the rpm enough and voltage is back in the 13 range. Apparently that's enough.



So. Decided to get a new alt, stop by harbor freight to grab a few tools and swap it. Fire it up and torqud reports 14+. Turn on everything, quick dip and recovers. Perfect. Time for a test drive.

1/2 block away, battery light and 12ish volts reporting. profanity ensues. Back to the house. Meter across the battery then alt case and stud, 12ish volts on both.

It's been a long day and I'm wiped out, so that's how she sits. Either the alt went belly up immediately or ive got a wiring problem.
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Old 05-27-2016, 10:48 PM   #8
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Check the pigtail with an ohm meter with the key in the off position one wire should have voltage the other one 0 amps with key in the on position both wires will have amperage if not then the issue is in the pigtail i peeled back the harness and had frayed wires replaced the pigtail and all is good on my car

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Old 05-27-2016, 11:37 PM   #9
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Pigtail was my thought as well, alt isnt getting energized. Ill troubleshoot tomorrow and hopefully will come to the end of this little path.
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Old 05-28-2016, 01:25 AM   #10
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Yeah was my issue came down to the pigtail lol

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Old 05-29-2016, 12:20 AM   #11
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Aaaaand brand new alt is dead. I spent some time today making sure i had voltage where it needs to be and 0 from the alt. Put the old back in and back to low/crappy voltage but it was working. In with the new, 0. I did that a couple times, same result each time.

Thank goodness the alternator is such an easy job on this car or else I'd be really grumpy. Parts place had to order a replacement in, hopefully tomorrow I'm 100% fixed.
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Old 05-29-2016, 02:25 AM   #12
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I'm not really surprised.
On a couple of occasions, I have gone through several rebuilt alternators before finding one that worked.
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Old 05-29-2016, 09:15 AM   #13
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Whats the best alternator brand to go with when it needs to be replaced?

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Old 05-29-2016, 12:25 PM   #14
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I just went with a lifetime warranty one from Orielly┬┤s

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Old 05-30-2016, 01:15 AM   #15
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New alt went in this morning, so far no issues. I'm holding judgement for a couple days on the original problems.

I believe the first alt was boxed car craft or similar, this one was tough something or other. Both reman from advanvced auto, this one was done in Mexico according to the sticker.
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Old 05-30-2016, 03:37 PM   #16
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advance normally carries driveworks as the 1 year warrany, made in china crap. carquest and toughone are the better ones carried in store. they offer reman as well as new. otherwise something like a denso or bosch unit can be ordered.
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Old 05-31-2016, 11:20 AM   #17
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Well, I've got a couple days of it running correctly so far. Still holding judgement but so far so good.
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