99 Taurus SE Acceleration problem w/AC running

[masmiley]

96000 miles. Today coming home from work had to break and then engine started losing power and RPMs jumping from 0 to 1000. AC stopped blowing cold air. I turned off AC and got off freeway. I was able to drive the next mile or two home with no problems with acceleration as long as I didn't try to turn on the AC. Any ideas?

[Millermagic]

I have a similar problem, just less so. WHen I use my AC I do notice a power loss.

Did you always use the AC? Seems like the compressor is like sticky.

[shorod]

Could be a sign of a faulty Idle Air Control (IAC)/Idle Speed Control (ISC) system or vacuum line that's bad. The IAC is supposed to open up some when the A/C or defroster are on, or if the steering wheel is turned to lock (as well as when the ambient temperature and engine temperature are cold). The A/C, defrost, and power steering all put a large load on the engine so the IAC throttles up to make up for the load at idle. If the IAC system is not working properly, you could experience an engine that wants to die at idle. However, since the engine speed is fluctuating, that might be indicating that the IAC servo IS working. I'd suggest checking the throttle plate and intake manifold for carbon build up. If the plate has a lot of carbon on the back side of it, you may have restricted IAC passages, etc. Clean the carbon and see what happens.

Also inspect all the vacuum hoses to be sure none are dry rotted, cracked, or broken. Replace any that are.

And for good measure, put a bottle of fuel injector cleaner in the fuel tank (well, not the bottle, just the contents). If it's been a while since you've had the car tuned up, you may want to think about replacing the fuel filter, air filter, check the spark plugs and wires. Based on the mileage, you're definitely due if it hasn't been done recently.

-Rod

[masmiley]

Plug wires were replaced at 60,000 miles and air filter less than 2,000 miles ago. I change the air filter at each oil change but am due for plugs.

I drove it over to the mechanics tonight and it performed well as long as the AC was not on...turn that sucker on and the best way to describe it is like someone sticking a broom stick in a turning wheel...like it locks up the entire engine; turn off the AC and voila! No problems.

I first thought I had a gear slipping but I think it's more than that. It is definitely related to the AC. I tried switching on the AC when I was in the driveway with it idleing and it definitely degraded the engine sound.

I know that these cars transmissions seem to start to have problems around this mileage. The torque converter was replaced in this one by Ford warranty at 56,000 miles.

[masmiley]

It's hot here in south Texas so the AC has been used quite a bit.

[corning_d3]

Maybe the compressor is on the verge of locking up. Did the A/C make noise before this happened?

[masmiley]

I don't recall whether it made a noise or not...I know it stopped blowing cold air, but when I turned it off and then in a few minutes tried it again it was blowing cold air.

I wasn't aware that the AC compressor could cause the engine to do this. It's never occurred on any other auto I've had (Chevy, Mazda, Pontiac).

[shorod]

The A/C compressor will load the engine when it engages. The compressor is driven off of the serpentine belt. However, it shouldn't nearly cause it to die.

One experiment you may want to try would be to unplug the A/C compressor clutch, then start the engine and turn the A/C on. Does the engine idle speed increase? If so, your IAC is likely working fine.

Just out of curiousity, monitor the battery voltage with the A/C off and again with it on. When you turn on the A/C, you are loading the electrical system as well. The compressor clutch remains engaged by electricity, the blower motor runs off electricity, and the cooling ran for the radiator/condensor uses a lot of electricity. If you have a weak battery (diminished capacity) this extra load on the charging system could cause the alternator to load the engine (slightly) and could cause enough of a dip in the system voltage to momentarily cause the computer to go goofy.

-Rod