2000 Taurus Engine Surge With AC On - FIXED

[Tim Martin]

Customer brought in this 2000 Taurus SE with a 3.0L (U) engine that the problem is that when the AC compressor cycles, the IAC ramps up engine rpm in a nasty way. There is no trouble codes in the computer, otherwise there is no driveability issues. IAC precent with a hot engine at idle is 39%, engine idling at 750 rpm. When the AC compressor is engaged, the IAC goes to 50% and 1000 rpm. When the vehicle is in gear and you are at a stop sign with your foot on the brake it creates a nasty surge. So far I have not found any vacuum leaks. PCM fuel trim numbers are 1-2% short term and -4 to +6 long term. I am extremely uncertain what direction to turn to. AC works extremely well.

[Jeff @ Able Auto]

I have a lot of problems with ford iac motors. Have you tried resetting the keep alive memory? i had one in some time back, customer had replace iac cause it said so on the internet. Still had a problem. KAM reset took care of it.

[Tim Martin]

Well, I had thought that a reset of keep alive memory was only a temporary fix.

While I am very familiar with the keep alive memory reset, I am trying to understand the whole thing.

[steven kiser]

see if someone has messed with the base setting. It could be a vac leak. The a/c could be pulling down and when cycles off it will rev up. iac could be stuck open.

[jbadenoch]

I've had issues with ford idles as well and in a lot of cases cleaning throttle plate with throttle/intake cleaner fixes the issue in about 80% of the cases. It's quick and easy to try. It's a Ford

[Tim Martin]

Yea, I did already clean the throttle body. Actually, if anything, it made it worse.

[brother bubba]

...

Did cleaning the throttle bore change the iac numbers ??? 39% is a little high. Optimum would be 30%.After a KAM reset the PCM should learn an idle strategy that gives the desired rpm when the compressor cycles on. The other thing is that the compressor normally doesn't tend to cycle off and on, leastwise in this part of the country. They run continuously.

...

[Tim Martin]

So, perhaps I need to be connecting my AC pressure gauges and checking pressures>

I did adjust the throttle position so that the IAC numbers are at 30%. Cleaning the throttle body did not change the numbers.

[steven kiser]

Tim, are you getting any idle change after starting? As a rule the Fords will idle high then curb down. If this isn't happening the IAC may be junk. A lot of times i see issues with these having a reverse surge , basically the idle is stuck high and the a/c pulls it down when it engages. I usually use a high tech tool to test it. I rap on the IAC with a wrench. I replace a fair amount of these for being stuck or slow. A vac leak will cause this as well. You may not be able to hear it so i usually spray carb cleaner around it to see if there is a change. Yes i've had a couple of flare ups before but a blow gun takes care of that. Being an old timer i've had a flamer or two so these little ones don't bother me. Had a carb off of a Buick one day and my boss decided to crank it over. The fuel was shooting right into the intake from the fuel line. Weak wires sparked the flame. the only way to stop it was pinch off the fuel since the intake was sucking in flame it didn't need spark but that's another story. Look for a stuck IAC or a vac leak. Check vac reading, i've seen internal manifold leaks do this as well. Good luck.

[Tim Martin]

Well, this engine starts, the rpms flare up initially and then die down to a nice idle speed. As soon as the AC compressor engages, it will flare up as much as 400 rpm and then die back down as soon as the compressor disengages. So long as the AC is not called for, there is no issues while you are driving or stopping at, say a traffic light or stop sign.

[brianp87]

Either the iac or the the clutch is short cycling. monitor voltage to iac when it happens to see.

[Tim Martin]

The fix for this one was to do a computer keep alive power reset and also a fuel trim reset as well as an idle air control reset. After I did that, the engine idled perfectly and any time an additional load was placed on the system the PCM immediately compensated for it by keeping the idle speed where it should be.

Thanks guys for the help.