Surging Idle, dies when idling and when stopping - Ford Mustang Forum
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post #1 of 14 (permalink) Old 12-05-2016 Thread Starter
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Surging Idle, dies when idling and when stopping

Hey guys, sounds like I have a common 4.6 problem here. My car ran perfectly a couple weeks ago when I parked it. I went to drive it the other day and the idle was surging between 300-1500, the AFR was down around 10.1-11, and it'd die out after surging for a minute or two. It was also dying when I'd come to a stop with the clutch in or the car out of gear.

I had been having issues with it dying when coming to stops previously, and cleaning the IAC would help for a month or two. So I figured the IAC had finally gone completely bad, so I replaced it. Put in a Motorcraft because it sounds like the generic parts store IACs are junk, and it's still doing it.

It starts fine, high idles at 1500 for a few seconds, drops to 1100 for a few seconds, then drops to normal, then starts surging and the AFR drops. I've checked for vacuum leaks and haven't found one. Any other ideas? I'm thinking TPS possibly

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post #2 of 14 (permalink) Old 12-05-2016 Thread Starter
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Just checked it out a little more. I unhooked the battery and let it sit for a few minutes, hoping it'd reset. Didn't help. I also unhooked the IAC while it was running and it died, telling me that the IAC is working properly.

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post #3 of 14 (permalink) Old 12-05-2016
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Ford had a problem with the bullitts and cobras where they would die coming to a stop intermittently. Their fix was to bend the throttle bracket which contacts the idle screw slightly to allow more air at idle, that may be the solution to your problem. If you have a tuner check your TPS sensor voltage KOEO and it should read around .9-1.1v with the blade closed, then steadily go to 4.5ish volts as you open the throttle. Good luck.

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post #4 of 14 (permalink) Old 12-06-2016 Thread Starter
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That'd be a good guess on the problem, but I'm not sure since I've had the car since May and the idle issue hasn't happened till 5 days ago. And it was after the car sat for 2 weeks. Unfortunately I don't have a handheld tuner to check the TPS either. Is there a way to check it with a multimeter?

I'm just thinking it has something to do with a sensor somewhere since my AFR drops to 10.5ish before it starts surging. It usually hovers around 14.6
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post #5 of 14 (permalink) Old 12-06-2016
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10.5 is pretty damn rich. heck/clean MAF maybe? I know that gets thrown around a lot and usually people try it with little or no results, but besides looking for a vacuum leak (which would more than likely result in the opposite, a lean condition) checking MAF is the first thing I'd do. That sensor is essentially the gatekeeper of your a/f ratio.
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post #6 of 14 (permalink) Old 12-07-2016 Thread Starter
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I'll definitely be cleaning the MAF this weekend. Hopefully it'll help. Any other ideas if it doesn't? I'm just not sure what else would make it run so rich
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post #7 of 14 (permalink) Old 12-08-2016
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Scan for codes?


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post #8 of 14 (permalink) Old 12-08-2016 Thread Starter
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Not yet. Planning on it this weekend as well
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post #9 of 14 (permalink) Old 01-21-2017 Thread Starter
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Alright, I'm completely lost here now. I've scanned for codes, nothing. Unhooked the MAF and it still kept doing it. Unhooked the TPS and still kept doing it. Replaced TPS, still doing it. Even went as far as clocking the MAF, no luck.

When I start the car, my AFR goes to 15.3 during high idle. Over about 20 seconds, the AFR drops down to 10.5-11 and it starts surging. Jumping from 200-1500 a few times and then dies.

I can try to get a scanner that reads the car while it's running. I'm maybe thinking O2 sensors now?

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Surging Idle, dies when idling and when stopping

What does it do when you're cruising down the road? Every time I had a bad O2 it wouldn't ever really run all that bad but it used a lot of gas and it smelled bad. Anytime I've had a vac leak I had to keep the motor revved up so it wouldn't die. Egr?

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post #11 of 14 (permalink) Old 01-21-2017 Thread Starter
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I only drove it on the road the first day I noticed it. Was fine when I kept it cruising, but would die coming to a stop.

Would a vacuum leak cause a rich condition? Also, would a bad EGR throw a code?
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I think a leak would more likely be lean, unless maybe "un-metered" air is getting in so the ecu thinks it's lean so it makes adjustments and ends up rich. An egr should throw a code a bad O2 should throw a code. I've had both bad and neither did though. If you only had a spare O2 sensor... Do you still have rear o2's? If you did I guess you could swap the fronts for the rears. The sensors themselves are the same so both will work as they should in the new locations.


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post #13 of 14 (permalink) Old 01-23-2017 Thread Starter
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Threw a live data scanner on it. Found both upstream O2s weren't working. Ran for codes again, and it had a P0059. Bank 2, sensor 1 heater resistance sensor.

Threw the car up on a hoist, found both upstream O2 sensor wires had been chewed through right at the sensor.
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Quote:
Originally Posted by Screaming04Gt View Post
Threw a live data scanner on it. Found both upstream O2s weren't working. Ran for codes again, and it had a P0059. Bank 2, sensor 1 heater resistance sensor.



Threw the car up on a hoist, found both upstream O2 sensor wires had been chewed through right at the sensor.


Glad you found it. At least you have a lot of new parts now.


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