Hello!

I have an 05 Escape 3.0L with 130k miles. I cleared check engine a few hundred miles ago and it has stayed off. I dont know the codes given before then.

The problem:

When A/C is off, engine runs and idles perfectly.

However, if idling and AC is turned on, RPMs drop to almost 0. this makes the engine almost stall, the AC compressor turns itself off, and RPMs go back up to normal idle. Then the AC kicks itself back on and that process repeats itself a few times until eventually RPMs settle around 700 and AC stays on. If I accelerate a little (or drive around) AC stays on and cools fine.

If I leave the AC on and depress the pedal to increase RPMs, the throttle seems to stick around 2000 for a few seconds before starting the process listed above all over.

I have just replaced with IAC with an aftermarket one. The only change is that the throttle is now also sticky when AC is off (with old IAC it was only sticky when A/C on)

I have also cleaned PCV, MAF, and checked for vacuum leaks with carb cleaner. I did not notice an idle change while checking for leaks (AC on and off). I recently had plugs, fuel filter, and air filter changed, and cleaned injectors. Also changed upper manifold gaskets (not sure about lower).

I cant notice any misfires. I have taken it to a few mechanics, including ford dealership where I live in Mexico (car was purchased in US) and the cant find anything.

Any ideas on what could be causing this? Thanks in advance!

Frank

 

dirty/broken EGR?

 

It's possible that the aftermarket IAC isn't functioning properly. They are known to be bad straight out of the box (there was a topic at another Escape forum within the last 6-9 months... new aftermarketIAC was bad).
Here's the topic & a quote: Escape 2.0 Stalling issue when ac is turned on at idle..
If you still have the old IAC, try cleaning it..... reinstall it w a good gasket. Often times cleaning the old one works as a test-check or temporary fix, until a Motorcraft IAC can be installed.

MAF sensor. Only use a MAF sensor spray to clean it & do not touch it.

 

MAF was cleaned with MAF cleaner.

I tried cleaning old AIC before anything else. No change.

Its close to impossible to get Motorcraft Parts here.

 

could this be relaetd to AC?

 

I have now disconnected the battery for 20 mins with brake pedal depressed to reset computer.

throttle body is very clean and no binds

I did notice something interesting. I pulled the AC compressor relay to see if the compressor was causing any difference.. When I turn the AC switch to on (only fan turns on since relay is pulled), the engine RPM's barely drop (100 rpm lower or so instead of 400-500 when the relays is in place) BUT, the RPMs still stick at about 2500 for a few seconds. With AC switch in off position, RPMs drop immediately when accelerator pedal is released.


I also checked the voltages for the TPS, with key on but engine off, they were, GND, 1.00vt, and 5.01vt

since i have 2 IACs I left one mounted on the throttle body while i had the other in my hand with the wire harness attached. Then I switched the IACs to compare. The both behaved the same way. As soon as I turned the ignition on, both valves opened slightly but there was no change when I turned the AC on.

The wire harness that connects to IAC gives a constant 12.4Vt when switch is on with car off, and 14.4 vt when car is on.

i found this on another forum:
KE3 CHECK IAC VALVE RESISTANCE - I got 11.4 ohms for both IAC valves.

--- Is resistance between 6.0 and 13.0 ohms? YES 11.4 for both IAC valves


KE4 CHECK IAC VALVE FOR AN INTERNAL SHORT TO IAC CASE -

Measure the resistance from either IAC valve pin to IAC valve case.

Is resistance greater than 10,000 ohms? YES for both valves.

But I am still having the same issues. Thanks for any help!

 

When you engage the A/C compressor, there is a signal sent to the computer that informs of the expected increase in engine load. The computer reacts to this 'message' by telling the IAC to increase base idle above 700 to compensate.
If the IAC is lazy or slow or over or under responds, you can get the idle jumping up and down as the computer, knowing what is happening by means of the ignition system crank position sensor and who knows what else, tries to compensate by sending differing signals to the IAC. From what I've heard the IAC is a 'duty cycle' thingy. It gets pulsed signal, kind of like a buzzer, to move the 'pintle valve' open or closed. If it is gummy or unresponsive, its performance will lag the command, and the idle will not be stable.
On the other hand, it may be working perfectly, but the load from the A/C compressor is more than expected. If the system were overcharged or the lubricant was diluted, or the bearings were going out, or the pistons losing their coating, the friction from operation could be more than expected, and more than the IAC can compensate for.
A test you can run is to put the transmission in a drive gear, emergency brake on, and wiggle the steering wheel back and forth. There is a switch that closes when the pressure in the power steering system increases. That signals the computer that there will be more load from the pump any microsecond now... Bump the idle to compensate. So, the idle rpm's should bump as the wheel is rocked back and forth just enough to engage the power steering {enough to load the system, not necessarily move the wheels back and forth}. It the rpms do bump, I'd think you have another problem.
There is supposed to be a connection between the HVAC control switch that enables the compressor clutch and the computer. Your machine acts as if the computer is being 'taken by surprise' when the compressor clutch engages, and thus the idle drops, or 'sags', and then tries to compensate with what it 'knows' about your particular engine to get the idle to 'normal' under 'normal' load. When the idle still drops, using normal parameters, it can only do so much to compensate.
I think your control head is not sending a signal to the computer telling that the clutch is engaged.
tom

 

how can I check?

how would that affect the RPMS staying high after I release the gas pedal but ONLY when AC is on?

 

If this:
"I did notice something interesting. I pulled the AC compressor relay to see if the compressor was causing any difference.. When I turn the AC switch to on (only fan turns on since relay is pulled), the engine RPM's barely drop (100 rpm lower or so instead of 400-500 when the relays is in place) BUT, the RPMs still stick at about 2500 for a few seconds. With AC switch in off position, RPMs drop immediately when accelerator pedal is released."

is what you are referring to, I would consider that the emissions control system can do funny things when engines are 'unloaded'. You remove your foot from the pedal, and the engine hangs for a second or two. Is it expecting the inertia of the vehicle {mass} to keep the rpms in check? Is it trying to 'smooth' the deceleration? Is it trying to avoid 'trailer hitching'? Did it do anything to the gear selection in the transmission? I dunno the answers to all those, so figure that you need to do a 'real' test rather than making one up. I do understand the reason you question what it's doing, but don't have a good answer either.
From the description I have winnowed, I'd say the IAC is not responding as quickly as desired. It should bump the idle when the A/C is engaged. It should not overshoot going to low-low rpms, because that means it is NOT responding at all to load increase, nor should it go to 1000 rpms in the other direction for the same reason. Get your hands on a scan tool that can read 'current' stuff, and see what the 'idle %' command is or what it has been doing. With a scan tool, you can check a pile of things that tell you what the computer 'sees', and what it is telling its serfs to do. If it commands 1% IAC and the engine races, you know its bogus. OTOH, if it commands 75% and the engine still wants to stall, or droop its idle, you know something is wrong. You may find that something else is drooling all over your best laid plans, such as an alternator that is dropping voltage or a bad ground that limits current or ... the possibilities are endless. Hope you are retired and have time to chase this one down. Ha. Even in Mexico, the labor costs to find a problem can be expensive if you have to chase for hours.
tom

 

thanks for the great info. I will try to get a better scanner tomorrow.

i checked the voltage on the TPS again but with the car running. I get the same reading with AC on or off, as expected.

at idle, im getting 0.92vt and it progressively moves to a maximum of 1.48 vt at almost wide open.

do those numbers seem normal?