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Mustang Problem Diagnosis Got a problem you can't fix? Post here and one of our members will answer as soon as possible.
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Old 07-28-2018, 04:05 PM   #1
quickcurrent
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2000 Mustang revs up in idle from 700 to 1100 in Gear

This 2000 Mustang V6 acts up really strangely when in gear on idle. It does not do this when in Park or Neutral, only when in gear and the accelerator is not in use. It will suddenly rev up from the normal 700 up to 1000, sometimes 1100 rpm.

The air filter is fairly clean.


I have cleaned the Mass Air Flow sensor with brake cleaner.


I have cleaned the Inflow Air Temperature sensor with brake cleaner.


I have taken the Idle Air Control Valve off, cleaned it first with brake cleaner and Q-tips, then later took it off again and dipped it in gasoline for half an hour, then used more Q-tips to clean it better, and finally used some more brake cleaner, so it's quite clean now. I tested it by plugging it in and turning the key to ON and I could see the switch move slightly.


I have also cleaned the throttle flapper with brake cleaner, and it works smoothly.

I have sprayed a soapy solution over vacuum hoses with no apparent leaks there.


The air intake tube moves slightly when the idle goes up (letting in extra air)

I get no trouble codes at all with my OBDII tool.

Any ideas what else could be causing this?
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Old 07-30-2018, 07:58 PM   #2
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Re: 2000 Mustang revs up in idle from 700 to 1100 in Gear

I see a fair number of members have read this but no one seems to have any ideas.

For the benefit of anyone that may be having the same issue, I'll post what I have done to correct this issue.

I have lost count of the number of times I have taken the air intake stuff apart and put it back together, cleaning this part and then that part each time. Some I have cleaned more than once, as it seems difficult to get all the gunk out with any one try. Last night I did a fairly thorough cleaning of the whole thing, air tube, sensors, switch, and throttle body. After all that cleaning, it still was idling a little high every few seconds on the driveway, but not as high as before. Today I took it for a 60 mile drive, both highway and city streets, without any sign of the idle problem. All seems good for now.

It's hard to tell what was causing the idle issue, but the lesson I have learned is that if you come across the same problem, just clean, clean, clean everything and anything that affects the air flow on its way to mixing with the gasoline. After years of dirt and carbon accumulation, that contamination starts to take its toll.

Good luck.
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Old 08-20-2018, 01:31 PM   #3
quickcurrent
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Re: 2000 Mustang revs up in idle from 700 to 1100 in Gear

Another update on this issue, if anyone is having the same problem.

The car's idle was OK for a couple of weeks, then it started doing it again every 10 seconds without fail. :-( It also started running quite rough!



So many sites list this problem as being caused by a variety of things, but none that I can remember listed the cause that was doing this on my car, so I will explain what I have done.


The air passage and associated sensors were all clean, all functioning normally. The gas passages were also OK; I had used a significant amount of fuel injector cleaner, so I knew the injectors were clean.


So I started thinking that the third part of the starting/running of the engine must be at fault. I took off the ignition coil pack, cleaned it thoroughly to inspect for hairline cracks or bigger ones, without any success there. The coil was visually good. So I tested the coils for continuity; all coils checked out OK. At this point, I decided to order a set of spark plug wires since I did not want to take those off, test them, and put them back, as they are somewhat of a b*tch to take off and put back on, on account of tight spaces/clips/plastic tubes. That turned out to be a great decision. The wires had over 100,000 miles on them, so I thought they should probably be replaced anyways. After spending half a day doing that job, the car runs fine - no more idle issues, no more rough engine running. I put on NGK silicone wires. The rubber OEM ones had seen better days. I didn't bother looking for any faults on them as I was panning to ditch them anyways; in fact I had to cut the three going to the passenger side of the engine because they were sandwiched between the engine and the firewall so tight there was no other way of getting them out. I routed the replacements a bit higher so they are easier to get at. These wires are not easy to replace individually as they are in sets of three with all the clips and all. So it's a good idea to make a sketch of where they plug in before taking them off. If anyone is doing theirs and gets the wiring connections messed up, let me know and I can help (made a diagram for my own future reference). Model years of the new edge style, other than 2000, may have the coil pack rotated 180 degrees adding to the confusion if you plan to use the YouTube videos. :-(
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