97 3.0 V6

only when a climate control function is used that requires the compressor to be on. the idle goes up to 2,000 rpms and stays there.

so with my ac running its like having a cruise control and impossible to drive. i have replaced the iac valve with no result. also i bought a hanes book and have been unable to find anything. scanned obd and it showed no faults whatsoever.

 

Is there something in the A/C circuit that calls for an increase in idle speed? On my Ranger (manual) A/C I don't hear the idle pick up with the A/C on.

Also, with my Sable (ATC) I don't see an increase in RPM's on the tach with it turned on.

 

on any vehicle when u run the a/c it puts a load on the engine which could kill it at idle, from what i gather the iac is told by a number of things when and how to regulate the idle, even the power steering plays a role in it.

if you dont see a rise in the rpms on the tach when you turn your a/c on, its because it has been perfectly compensated for. idle speed 600 rpms. idle speed with a/c drops to 400 rpms. therefore computer instantly increases rpm by 200 and you dont notice anything.

so mine is somehow getting too much of a signal, that is my guess.

what i need to know is what exactly communicates with the pcm or iac when i flick that switch. is it the a/c cycling switch, low pressure switch, maybe some other sensor that is going haywire? its ice cold, and the reading with my freon gauge shows normal.

 

I'd maybe suspect an acting out IAC.

 

Not sure if this will help or not. According to my 2000 wiring manual, inside the Battery Junction box there is a WOT - A/C clutch control relay. Maybe it's starting to go bad and your IAC is holding the RPM's to 2000.

There is also an A/C clutch field coil that has this note, (With voltage applied, energizes compressor clutch. Sends signal to PCM to adjust transmission EPC pressure to compensate for increase in engine load).

 

i went ahead and replaced the iac with a brand new one from napa today and the problem still exists. although now the engine idles a bit high at all times. with the screw backed all the way out on the throttle linkage the base idle i would approximate is 800-1000 rpms. with the iac disconnected and the screw backed all the way out the engine speed drops very low but does not die.

 

OK, I'm not clear on whats happened & when. Right now I'm thinking maybe you have more than one problem.

SO, was there a problem with idle speed Without the AC on, with the first new replacement IAC????

Did you do the IAC idle speed disconnect test before you bought the first replacement IAC, or just after you bought this last new one????

The computer controls the on/off duty cycle on the IAC operating voltage, to control how long it's open, to bleed air past the throttle plate & thus control idle speed.

If there is a vacuum leak, or a sticking throttle linkage or throttle plate, or the IAC acts out, that'll upset idle speed.

On your initial post, about it only acting up when you turned the AC on, made me think it might be the IAC, but I suppose it could be a vacuum leak in the in cabin Heater/AC control panel, so maybe find it's under hood vacuum line & disconnect & plug it & see what happens.

On the new IAC high idle at all times, did you get & use the gasket that comes with some new IAC's, or did you just leave the origional "O" ring seal in place???? Are you certain the present new IAC sealing surface is clean, no nicks, or seal/gasket damage????

Did you pull the battery B- cable, to wipe the computers memory & turn off All electrical loads & go through the computers cold & warm idle relearn proceedure, so the computer could relearn it's cold & warm idle strategy with the new IAC?????

 

paw paw. 2 weeks ago i bought a new one from autozone, and slapped it in. thinking the new one could be bad as well i took it back to the store, and then this week i went to napa instead, and bought one there and it still didnt fix the problem. and so now um.... haha like a jackass i may have to return it. terrible way to try and troubleshoot i know, i aint gonna go crazy replacing anything else. but from all the research ive done online, and reading books, that is what everything was pointing to.

who knows if anything in the a/c is to blame, but wierd it only happens with it on. regaurdless, besides the power steering pump pressure switch, or cold engine high idle function, i have no idea what else to take a look at, or even how to check it. hanes books are garbage. nobody else including a mechanic in my family that lives too far away, has any idea what it could be.

yes i have done that test a few different times and disconnected the battery terminals for a half hour as well.
problem only occurs with a climate control function that requires a/c. car is fine otherwise. problem happens when its cold out, raining, or winter as well, but not as bad, rpms are high but not screaming. the pcv valve is in good shape, and i squirted all vacuum connections with a spray bottle as well as listen for leaks. yes i scraped off old gasket and used new.

 

OK, after you disconnect the battery, to wipe the computers memory, do you wait until the engine has completely cooled down & then turn off All electrical loads, including turning the heater/ac control to Off, before beginning the computer cold & warm idle relearn strategy routene????

 

If you've done the proper cold & warm idle relearn routene, , so your certan the computer has the proper base idle strategy, then move to disconnect & plug the under hood heater/ac control vacuum line, then turn the AC on & post what happens.

 

Not to take away from Danger's problem, but how do you perform the proper cold & warm idle relearn routine? I am watching this thread with interest.
Thanks,

 

Cold & Warm Base idle relearn routine:

Let the engine completely cool down, turn off All electrical loads & wipe the computers memory by disconnecting the B- cable for at least 15 min, if it's hasn't already been done, or open a door, turn a light switch on, or push the cigar lighter in, to provide some resistive load to discharge the KAM memory faster.

Then turn off All electrical loads so you won't make a spark or cause an electrical surge & reconnect the B- battery cable.
Start the engine cold, let it idle down some, then slowly shift into each gear, including Reverse, long enough to feel each gear engage, ending in "N" or "P" & without touching, moving or turning anything on, let the engine fully warm up, then slowly shift into All gears again.

This will enable the computer to properly relearn its cold & warm idle strategy after a KAM memory wipe.

Ford also has a rather extensive "drive cycle" routine here Ford Motor OBD-II Driving Cycle | Car OBD Diagnostics, ECU Chip Tuning & Auto Repair Support but I've never had any driveablity problems if I perform the cold & warm idle relearn, so never have done it, or needed to use it if first doing the idle relearn routene.

One might have to do it if your trying to reset all the IM monitors, to pass an emissions test shortly after a memory wipe, or are having adverse driveability problems.

What we need to know or establish in this case is if the computer has learned the proper base no load idle strategy. If it's relearned it with the AC on, it might want to over rev the engine when the AC is turned on.

If the base idle is ok, then I was looking to try & isolate a vacuum leak in the heater/ac control panel or actuator, by having him disconnect & plug it's engine vacuum source.

If that solves the idle over rev when the AC compressor turns on, then the problem is likely somewhere in the cabin around the heater/ac control panel, or it's vacuum line connection to the blend door, or maybe it's vacuum actuator.

So that's kinda the method to my madness!!!! lol

 

Thanks PawPaw

 

thanks paw paw. i will go ahead and look into that. but will that allow the blower fan to run while to doors to the duct are shut?

what i realized is i need to learn every single component that orders a idle increase, how much the increase is, what the level of the signal it sends should be, be it voltage etc. by investing the money on a better book, and until all of these parameters are met i will be stuck sweating it out!

....then take a systematic approach to solving the problem, starting with the easiest, working towards the hardest.

 

paw paw. i have completely ruled out vacuum leaks as a possibility.
with the iac valve disconnected, and the intake holes plugged, if i turn the a/c on the problem does not happen. so the only possibilty at this point is the ecm which controls iac operation, which is not likely because ecm's rarely go bad. the other possibility is one of the many sensors that contribute a signal to idle control, and when the a/c is turned on, something goes haywire and sends the idle through the roof. the problem does not happen with the a/c off, so can i rule out those sensors and overlook them?