Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2002 Taurus high idle

Engine code U. 220,000 miles. Out of blue I have a really high idle. I am a retired computer guy and have tried to service my own cars. Idle 1800, after clear 2200.

I have a Bosch 1150. I ran some tests to see if I could tell but no codes had been set. Later it did code P1506, P1504. IAC has not effected idle plugged or unplugged.

I replaced the pcv valve and visually looked at hoses and sprayed looking for leaks. Then I cleaned mass air flow, throttle body with the correct sprays. I reset the codes which was a mistake. Unplugged battery while I cleaned and disconnected.

I took a drive and made recording of four tests, drive test was not complete so I still I have drive code.

I wondered if something could be interfering, tested the charging system on a new Costco battery
Best I can tell the alternator is crapping out and must be effecting IAC. I ordered a alternator. Snow storm coming did not check with load or check the resistance or the voltage on my IAC. Or I did not check the voltage at the alternator or going to the IAC.

Any suggestions, insights, tips? I will pick it up after the storm and I install the alternator


In all honesty, I think the first thing you should do is replace the IAC valve

it’s simple and cheap, and a common failure item.

Be aware . . . if you buy the IAC valve from Ford, you WILL have to buy the gasket separately. They are cheapskates like that. However, if you buy an aftermarket IAC valve, it will come with a new gasket.

I would install that IAC valve before the alternator

If it takes care of all of your problems, you can presumably always return the alternator . . . or at least save it for when you do need it

3.0 liter Vulcan ohv V6, correct?


Start the engine, and let it get up to operating temperature.

While the engine is idling, take the handle of a screwdriver and rap on the IAC valve.

If the engine idle speed changes, replace the IAC valve.


1 Like


I thought U was only on Vulcan 3.0. But correct.

Last week I drove after dark and my lights were very dim. The values on that test show a weak charging system.

The 1504 code refers to a faulty electrical connection which a weak to intermittent current would reflect.

I guess it could be both. The alternator seems to only put out the minimum which may not be enough juice to operate it. Plus it’s an old car so I need a smoker to really be sure no leaks.

Do you not agree the charging system is weak? The running voltage never got to 13.7 but once when the idle was at about 2200.

And thanks for the tip on the gasket.

I will try that. Thanks

That’s seems to be your problem. The plunger/valve might be stuck.

Could be. We got a foot of snow over night. It will be a few days before I can get to it.

THe best way to test your charging system…is with a DVM. Check the voltage at the lug on the back of the alternator while the engine is idling. You should get about 13.5 volts.


High idle rpm usually is either the IAC function (however that is done on your car), or a vacuum leak. There’s always an off-chance it’s the pcv valve, so you were right to replace that part. You could try spraying starter fluid here and there on the engine, if the idle rpm increases in one particular spot you’ve found the location of a vacuum leak. I had a high idle problem on my Corolla one time that was caused by a faulty IAC device in combination with a faulty thermostat. One input to the IAC is the coolant temperature, and if it is colder than it should be the IAC will increase the idle rpm.

I tried to cover all my steps. Thanks. I plan on wacking the iac once I can get to it. Over a foot of snow covers it now. I am fairly curious how all this turns out.

You really need a smoker if you are going to drive old modern cars. Mental note made.

Doesn’t coolant circulate through the IAC valve on your 1992 Corolla . . . ?

He says themostat

Yes it does

Well today besides shoveling a foot of snow off driveway I bought a IAC from AutoZone. Hooked it up and no start … period. Cranks and cranks. Yes it is tight, gasket in place and plugged up

So I put old one back on and it cranks right up and in a minute or so goes to about 2000rpm and stays there. I turn it off fairly quick. If I pat accelerator it just goes higher.

It seems the replacement part is worse than the original … lol … sorry, not making light of the situation, but just more proof that when it snows, it snows bushel baskets. Faulty replacement parts right out of the box is not an uncommon thing reported here. Take it back and try another one is what I’d do. Have you tried cleaning up the original IAC? Sometimes they just get gunked up with engine crud.

On your car the IAC is probably computer controlled. The computer decides how much to open it (speed up the engine) depending on what it thinks is the coolant temperature, which it gets from the coolant temperature sensor. Good idea to take a look at that connector to make sure it hasn’t fallen off or otherwise damaged. CTS’s are rare failure items, but its electrical connector could be problematic.

Another idea, sometimes replacing the IAC requires an initial calibrating procedure of some kind. Usually involves a scan tool. Sometimes just disconnecting the battery will cause the computer to reset, and they’ll do the initialization upon reconnection. The computer has to know at some point what position it is originally in. Maybe that’s why your replacement part didn’t work. Took a quick look at the service data for the v6 3L engine, and don’t see anything about an IAC initialization needed however.

Thanks, I will find that coolant sensor.

Yes I cleaned it. Seemed the right thing to do. I used that special throttle body cleaner.

I am hopefully getting it smoked tomorrow, maybe he will share that sensor location. I suspected that was a crappy part
Maybe I can find a motorcraft.

If the IAC is faulty, the computer would be able to determine that b/c it knows what the engine rpm is, and what it has been programmed to be based on the coolant temperature, alternator load, transmission shifter position, etc. If those didn’t match, it would throw a code. With no codes and high idle rpm seems a pretty good chance the problem is the coolant temp sensor. If that was the problem the computer could think the rpm should be high, b/c it thinks the coolant temperature is -20 degrees, when if fact it isn’t.

I just remembered I have a 2005 Taurus. I am going to switch iac over to the 2002 and see what it does. If it works I will order a motorcraft from Walmart for 67 and be done with that part wish I had thought of that switch earlier, better later than never.

I was unable to find any coolant sensors that work with the 2002 iac. Will keep looking.well their is dash gauge sensor only feeds the dash temp gauge

I am asking Me/santa for a smoker. I have a code reader just not bio directional and that is a fault need one of those two.

I borrowed the iac from my 2005 car and now the 2002 now idles fine.
Thanks to all for you suggestions

Good for you. It remains a puzzle why the faulty one didn’t cause a code to be thrown.

Smoke testers are a good start, but aren’t guaranteed to find unwanted air leaks into the engine. There are devices on cars that purposely allow air leaks into the engine to increase the idle rpm, the power steering pump for example. There’s a pressure sensitive air valve inside the PS pumps that opens whenever the steering wheel is turned. If that valve got stuck open it could cause high idle, but I’m doubting whether a smoke machine would show it. The air source for that valve comes from the air filter ass’y, and maybe some smoke would eventually show up there, don’t know.