03 Explorer 4.6 Super high Idle nothing works so far

[Maxim63]

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

 

[Gmctyphoon]

I would disconnect the pedal and cruise control cables from the throttle body and start the truck. See where it idles then.

 

[Maxim63]

I would disconnect the pedal and cruise control cables from the throttle body and start the truck. See where it idles then.

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.

 

[Donystoy]

My first thought is the TPS but you have already changed that. Hard to believe that the speed stays up with the throttle cables off and the throttle body assumed to be totally closed.

 

[94Eddie]

My first thought is the TPS but you have already changed that. Hard to believe that the speed stays up with the throttle cables off and the throttle body assumed to be totally closed.

If the throttle is closed then the only way a high idle can occur is from a vacuum leak or a malfunctioning valve. Maybe spraying carb cleaner in various locations will give a sign as to where a leak is occurring.

 

[Gmctyphoon]

If the throttle is closed then the only way a high idle can occur is from a vacuum leak or a malfunctioning valve. Maybe spraying carb cleaner in various locations will give a sign as to where a leak is occurring.

I agree, it must be a major vacuum leak. After or before spraying carb cleaner, try disconnecting the brake booster hose from the booster and cap it off. I guess it could be a bad brake booster.

I see absolutely no way that an Ecu can cause this problem on a drive by cable engine. Also I have replaced my temp sensor on a 4.6 because of weird readings. Still had weird readings with new sensor. I’d forget about the temp readings for now.
Remember the 4.6 doesn’t actually have a temp sensor that reads the coolant.

At this point your problem is a bad throttle body (unlikely) or a vac leak.

 

[Maxim63]

I agree, it must be a major vacuum leak. After or before spraying carb cleaner, try disconnecting the brake booster hose from the booster and cap it off. I guess it could be a bad brake booster.

I see absolutely no way that an Ecu can cause this problem on a drive by cable engine. Also I have replaced my temp sensor on a 4.6 because of weird readings. Still had weird readings with new sensor. I’d forget about the temp readings for now.
Remember the 4.6 doesn’t actually have a temp sensor that reads the coolant.

At this point your problem is a bad throttle body (unlikely) or a vac leak.

I will take a closer look at the booster, hard to spray the carb clean when the engine is racing already but I’ll try. Also wouldn’t a smoke test reveal a vacuum leak that bad? I have gotten it smoke tested by 2 different machine and no leaks found.

 

[Gmctyphoon]

What does it do with the iac electrical connector unplugged?

Your right, a bad vac leak would show with a proper vac test.

 

[Maxim63]

So quick update, had a friend come over with his Snap on Scanner and we could not establish communication with the ECU, he tried multiple times. I am sourcing a ECU now and am going to try it and see what happens.

 

[Maxim63]

What does it do with the iac electrical connector unplugged?

Your right, a bad vac leak would show with a proper vac test.

it idles poorly but will stay running for a few minutes with IAC unplugged, same if I disconnect the MAF goes into a sort of limp mode.

 

[Maxim63]

I will take a closer look at the booster, hard to spray the carb clean when the engine is racing already but I’ll try. Also wouldn’t a smoke test reveal a vacuum leak that bad? I have gotten it smoke tested by 2 different machine and no leaks found.

the ECU controls the idle via the IAC depending on what it reads from the 'inputs' such as air temp, coolant temp, throttle position ect. So if the ECU is reading that it is -40 air or coolant it wants to raise the idle via IAC which is post MAF so it lets in more air to the throttle body after the throttle plate so the plate can be completely closed and air is still allowed into the engine in large quantities.

 

[iowa_hick]

I just logged on to ask about a similar, but not as severe issue. Mine idles around 2000 RPM. I replaced the IAC with a motorcraft one, and the problem is still there. If I unplug the IAC, mine drops down to between 600-800 RPM.

 

[Maxim63]

So quick update, replaced the ECU and got it programmed to the vin. No change still idles high so I am at a complete loss i am open to any suggestions at this point I have too much time, money, and sweat invested to just get rid of it (it has crossed my mind) I have a feeling its going to be something simple that Im just not looking at. The problem has not changed since it has started and all the parts that I have thrown at it has had no effect.

 

[94Eddie]

How are you checking for tripped codes? You might need to have it scanned with a high end scanner by a person very knowledgeable in reading codes and real time data outputs to find the problem. I think there is something that a good mechanic can trace to which will solve the problem. The hard part will be finding the right person to do it.

 

[Donystoy]

I agree that this engine requires a proper scan of the codes which a store bought code reader might not be showing. I wonder if there is an issue with the fuel pressure which is causing too much fuel delivery. Try to determine what the pressure is and compare it to what is specked. Just sold my Explorer last week and gave my manual to the new owner. If there is a pressure sensor or flow meter it could be faulty and giving the ECU a false input. As I said no manual or electrical schematics so just guessing at this point.

 

[94Eddie]

I agree that this engine requires a proper scan of the codes which a store bought code reader might not be showing. I wonder if there is an issue with the fuel pressure which is causing too much fuel delivery. Try to determine what the pressure is and compare it to what is specked. Just sold my Explorer last week and gave my manual to the new owner. If there is a pressure sensor or flow meter it could be faulty and giving the ECU a false input. As I said no manual or electrical schematics so just guessing at this point.

I see the really knowledgeable mechanics on YouTube using a high dollar scanner to ferret out tough to diagnose problems. It is impressive how they look at embedded codes but the impressive thing to me is watching them analyze real time data output while the engine is running. There may not be a code tripped but they look at the readouts and find the issue.

 

[Maxim63]

My buddy has been using a autel maxisys and a jbox to read codes data and program.

 

[Gmctyphoon]

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.

 

[john cris]

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

Check throttle linkage in footwell

 

[Gmctyphoon]

Check throttle linkage in footwell

As previously stated he disconnected both cables from the throttle body with no change..