03 Explorer 4.6 Super high Idle nothing works so far

[Maxim63]

So you say that if you unplug the iac then the idle is not 2500 to 3000 rpm?

If that’s a yes, then obviously it’s something related to the iac. You changed the iac many times so that’s not it. You changed ecu so that’s not it. But there’s wires going to the iac. If some of them are shorted out on each other that could make the iac open al the way. Also I’d be interested to see what a real code scanner reads the rpm at. It’s possible that the ecu thinks the idle is actually at 800-900 rpm. But it’s really at 3000 rpm. A snap on or similar scanner will read rpm from the computer, not the tac on the dash. I believe this is unlikely but I guess it’s possible. If it’s the case then it sounds like the crank sensor might be bad. But again I think this would be shocking if it were actually the case. Just something easy to check which a scanner.

If it was at my shop I would do a pin out test on all the wires on the iac and make sure non are shorted out first.

All of this assuming that the idle goes down with the iac unplugged.

I can check continuity between the wires from the connector at the ecu to the connector at the iac, that is if there is a direct connection, because I don’t have a BOB to do a full blown pin-out. I peeled back the loom down to where it meets the bulk of the harness from the iac connector to make sure no breaks or frayed wires, all good. I wasn’t too thrilled about right where the wires go into the connector they looked bent so I might just snip off the connector and solder in new one for peace of mind.

 

[94Eddie]

Another thing to check is the throttle plate to make sure it is completely closing at idle while the vehicle is running.

 

[Gmctyphoon]

I can check continuity between the wires from the connector at the ecu to the connector at the iac, that is if there is a direct connection, because I don’t have a BOB to do a full blown pin-out. I peeled back the loom down to where it meets the bulk of the harness from the iac connector to make sure no breaks or frayed wires, all good. I wasn’t too thrilled about right where the wires go into the connector they looked bent so I might just snip off the connector and solder in new one for peace of mind.

Do not cut wires and add new plugs till it’s diagnosed. Your just doing more work and creating more problems if so.

 

[Gmctyphoon]

So you never re-answered, it idles down when when you unplug the iac?

 

[Maxim63]

So you never re-answered, it idles down when when you unplug the iac?

Yes the idle drop, idles erratically but does drop significantly almost to normal

 

[Gmctyphoon]

Find the issue with the iac circuit or pay someone to and problem solved

 

[Gmctyphoon]

 

[Gmctyphoon]

So I meant to post those hours ago but I got busy, sorry.

I also just looked at the wiring for the first time just now. The violet/white wire gets ignition power from fuse 39 under the hood, not the PCM. But the white/light blue wire is a negative variable trigger from the ecu.

I would unplug the Ecu plugs and unplug the iac plug. Then test the white/light blue wire at the iac plug and see what it reads. If should rear nothing. If it reads 12 volts negative then you have a problem. Use a meter to test. Report back.

 

[Gmctyphoon]

So how’d you make out?

 

[Davies0202]

I tried what you said, no change. I replaced the aftermarket IAC with a Motorcraft one still no change, tried a ford MAF still no change. Im starting to look at the ECM as the culprit, my temp inputs are all over the map each time I hook up the code reader so im thinking the ecu isnt processing the inputs properly and causing the issues.

This isn’t related to the high idle issue but my code reader couldn’t read codes either and it was just a fuse under the dash that can go bad with some phone chargers in the cig outlet that’s what blew mine atleast

 

[MakinJeepsWeep!]

Have you cleaned the TB? along with maff and air temp sensor. Also even the o2s can effect idle, they can get bad before they show bad with a code.

 

[Maxim63]

So I had it towed to Ford after months of frustration. They had it for 3 weeks and determined it is a wiring harness issue even though they cannot pinpoint the exact area or wire that is damaged. Since a replacement harness is no longer available through Ford the remedy they gave to me was either sourcing a used one or removing the harness and opening it up to find the issue. So it’s being towed back to my house today and I plan on removing the harness and working on it. I’ll take pics if and when I do find the issue.

 

[Gmctyphoon]

2 months ago I said it was a wire harness problem. And listed diagrams and how to diagnose it...

When there is “A Wire Harness” problem the dealer will only remove and replace. A good independent shop will find and fix the problem, without replacing the harness. You only have an issue with one or two wires. No need to remove the harness, that will just cause many more issues..

Call around, find a shop confident in this line of work and have them diag a fix it.

 

[ataw10]

My 03 Explorer 4.6 is idling super high 2800-3000 rpm upon start up and does not come down, I can not even put it into gear because it’s reving so high. So far I have put a new intake manifold, iac, tps, maf, egr valve, egr pressure sensor, 4 o2 sensors, cylinder head temp sensor, pcv, all vacuum hoses , removed cleaned and lubed throttle body, smoke test (no leaks), did a battery rest All and still no change, the issue came out of no where it was running like a champ and one day I parked and when I restarted it was idling high and i barley made it home. No DTC’s I’m all out of ideas any chance you guys can point me in the right direction

im doubtful the computer would make it idle that high , theres got to be a darn leak somewhere but maybe try this 1st for the hell of it disconnect both battary wires tape them together with them both having contact leave it for a hour or over night, might reset pcm an fix issue

 

[MakinJeepsWeep!]

Okay i guess i missed where You need to start running wires like he says here. I think thats your ticket.

2 months ago I said it was a wire harness problem. And listed diagrams and how to diagnose it...

When there is “A Wire Harness” problem the dealer will only remove and replace. A good independent shop will find and fix the problem, without replacing the harness. You only have an issue with one or two wires. No need to remove the harness, that will just cause many more issues..

Call around, find a shop confident in this line of work and have them diag a fix it.

 

[Maxim63]

Problem Solved, heres the update and eventually the fix, tried running wires no change tried replacing the main engine and transmission harness and you guessed it no change still idles high. I began really studying the wiring diagrams and went sensor by sensor to all those affected and found the culprit after months of searching it turns out the cause of all my issues was a defective Ford DPFE sensor (previously diagnosed and replaced) that was internally shorted and caused all the other sensors to read high inputs so my high idle was actually caused because my temp sensor (on the same circuit) was reading -40 because the DPFE sensor intercepted and sent a erroneous signal to the ECU. So if there is anyone else out there with a 4.6 and you have a high idle and people keep telling you its the IAC (even though you have replaced it with a Ford one twice), do yourself a favor and take a ohm reading to your DPFE it just might be the cause. Thank you to all the input from this awesome forum it was all good info, especially GMCTYPHOON for the wiring diagram.

​

hopefully this helps someone else out there.

 

[94Eddie]

Thanks for reporting back with the fix! It will help a lot of people as time passes.

 

[MakinJeepsWeep!]

Glad to hear it and great info! I have that on my 01 b3000 if it gets funky I'll check that thing out!

 

[mountaineer2004]

Wow, great troubleshooting skills!
Glad you tracked down the problem, and posted the answer for others.