I have read "when replacing" a IAC valve one should disconnect the neg. side of the battery after installing to let the computor re-callibrate the change over for 15 min.

Does anyone know if this is fact or fiction? I have also been told that the computor does a scan every fourth start up for changes and malfunctions and the disconnect is not required.

I see some logic to both , but what is the right thing to do?


THX. cobrah

 

Homer can correct me if I go astray....

You should reset the PCM (disconnect cable). Here is what happens: the engine computer is programmed to supply fuel and spark over a wide variety of conditions (one of them being idle). It has what is called an 'adaptive strategy', which is a fancy way of saying that it can learn. What does it learn you ask? Take for example all of the variables involved; in your case does the old IAC open up just a little more or a little less that the old one? The computer learns these difference from the feedback (all of the inputs) from the various sensors on your motor.

Here is what you should do: disconnect the neg side of the battery cable (about four seconds works for me). Start the engine (after reconnecting the battery cable of course). If after one or two seconds of the engine starting your instrument needles jump to 'full scale' and then back again, your PCM has been successfully reset. Let the engine reach operating temperature than shift from P to R. Hold your foot on the brake for one minute and the PCM will learn the 'in-gear' idle. Next, without removing it from being in gear engage MAX AC and hold for another minute. Your PCM has now learned its idle strategy.

(The same goes for the trans after you drive it around for a bit.)

 

Thank you for the GREAT advise, I knew someone had the answer... some real " sharp " folks here. This site has saved me a lot of time and labor not to mention $$$!

cobrah

 

We've all done it... set the screwdriver or ratchet a little too close to both battery terminals... then accidentally bump it and create the mini fireworks display.

One should always disconnect the battery when working on a computer-controlled engine. If for no other reason than to keep an accidental electrical discharge from frying the computer.

 

Hmmmm, seems to me it wouldn't matter if the cables were connected or not if I set a conductive object near the battery terminals. Agreed that one should disconnect when working; especially when wiring (air bags) or working around the alternator.

Ah, now I'm hijacking the thread.

 

It won't matter to the battery, or to the item shorting across it, but if you have the cables disconnected from the battery you shouldn't affect anything else on the vehicle.

 

Sorry, my post wasn't too clear...

As BroncoBob pointed out, disconnecting the battery cables will keep that sudden surge of electricity (when "shorting" the battery) from traveling through the truck's wiring back to the electronics. I've read more than one report of someone having that happen. It's a lot cheaper & easier to disconnect the battery cables than to replace an ECU.

 

I had a mechanic work on my 5.4 (minor) and I stopped by to see where he was on the job, and how much longer it would be.

I noticed right off the battery was disconnected...he said that was to protect the computor.

I picked up the E.B.4X4 that afternoon and later I noticed my compass was hung up on N position. It worked fine prior to disconnecting the battery.

About 3mths. later... I found out how to reset it! The book does not cover this either.

So if anyone has a hung compass...I can give ya the formula to fix it!

But my point is, disconnecting the battery can lead to other problems.

Da cobrah

 

Cobrah,
I'm interested to know how you reset your compass. Mine is constantly reading NE and I just removed it today and found a red button inside it. I hit this button but it still reads NE.
regards,
clittle1@cfl.rr.com

 

First you will need a larger paper clip, and a lot of room to drive around in a circle.

My compass was hung up like yours for months, and I got a tip from a ford man who was a salesman or machanic. I followed his advice and WALLA!!!!

A vacant parking lot, or baseball field will do.


You should look at the little black box at the base of your mirror, further look for the small reset hole, it has one so don't give up.

Pull one wire from the paper clip outward and use the remainder as a handle.

Now your ready...you can go in a circle clock wise or counter, whatever way your comfortable. push and hold in the reset button described above with the paper clip and continue to circle.

Small configurations will appear in the right hand corner of the display,release the reset, do not stop, continue to circle.

Your compass should began to read the multiable directions as you circle. I had to do it twice but it does work. Don't be in a hurry after you release the reset look at the directional letter. If your making a tight circle then the change will be more frequent.

Best of luck and let me know how ya come out. Oh yea, I was told about the "formula" by (one of our own) at this sight... You can be sure that if it can be fixed... someone here knows how to do it!!!