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Ford Taurus 2003

I’m having trouble with my Taurus 2003 and the mechanic is struggling to find anything wrong;
When idling, if I turn on the A/C on the car will start to shudder intermittently. It feels kinda like an engine misfire…
The mechanic replaced the spark plugs and the trouble seemed to disappear but was back again after a number of weeks. When I took the car back the oil-seal was leaking so I got those replaced. It may possibly have been better for a few days [It’s a bit difficult to gauge as the problem is somewhat intermittent] but then the problem was back.

Does anyone have any ideas/experienced anything like this?


The problem might be with Idle Air Control valve.

The IAC valve controls the engine idle speed under all conditions.

For example, when the AC is turned on, the load the compressor imposes on the engine may cause the engine to run rough or even stall. The IAC valve raises the idle slightly to prevent this from happening.

One way to check for a bad IAC valve is, when the AC is on, and the engine runs rough, take the handle of a screwdriver and rap on the IAC valve. The idle picks up or the engine stalls, replace the IAC valve.


Clean the throttle body and the IAC

If that doesn’t resolve the problem, replace the IAC

Thanks, I’ll give that a try as it sounds like it could be it as the problem definitely seems to be related to the load on the engine as the harder the a/c is working the more likely it is to run rough.

I tried tapping of the IAC valve and it didn’t seem to make a difference. Though seeing as the problems you described sounded right, I replaced the IAC valve and no change at all unfortunately…

Any other ideas?


“The mechanic replaced the spark plugs and the trouble seemed to disappear but was back again after a number of weeks.”

Next, I’d try spark plug wires (if not coil-over-plugs), then coils.

Try cleaning the Maf with sensor safe cleaner. Are there any codes? You can get them read free at Autozone or Advance.

Thanks for the responses,
Unfortunately the spark plug wires and coils were replaced as well.
I’ll try cleaning the MAF sensor and see if that works. The engine is showing no codes at all.

New plugs, wires, coils will almost always cure miss. Did u have flashing CEL when the motor was stumbling?

No flashing CEL either!

I cleaned the MAG and the throttle body this weekend and no change either :/.

So to sum up so far what’s been tried;

  • Replaced Spark plugs, spark plug cables, ignitions coils
  • Tried new IAC
  • Cleaned MAG and throttle body
  • Replaced the air filter while I was at it

All of which didn’t fix the problem. There’s no CEL and no engine codes. That said the problem is definitely still there, if I turn on the a/c while idling the car starts to sporadically run rough.

Any other thoughts would be appreciated, as this really seems to be a obscure problem!

Tell your mechanic to monitor the engine for misfires when the engine is idling with the A/C on using the cylinder contribution test found in the menu of his scan tool. A good examination of all the scan data for the fuel and ignition systems will tell you if the problem is related to engine operation or perhaps the A/C system.

I would also want a set of A/C gauges hooked up to the system while this is happening.

OK, try 2 bottles (double dose) of Techron fuel system cleaner in a full tank, or a “fuel injection service” at your garage if you want to go that route. Then there’s the EGR valve…

Good news!; I did the double dose of Techron fuel system cleaner suggested by insightful and it seems to be running fine! I’ve driven the whole tank with the cleaner and filled up with gas again today and so far haven’t seen the issue anymore! I’ll keep an eye on it over the next few weeks to check it’s not just coincidence, but I’m optimistically considering it fixed!
I’d tried some type of fuel system cleaner before but perhaps it needed an extra kick!
Thanks so much insightful, tester, db4690, knfenimore, Cavell, asemaster for your time and patience, I really appreciate it! :slight_smile:

I had the same issue for months. I replaced IAC, cleaned throttle body, changed plugs and wires, replaced coil pack. Problem did not go away. Fuel pump died months later. I hoped a new fuel pump might solve the problem but issue was still present after pump was replaced. I broke down and took it to a shop. It turned out to be the pcv valve and hose causing the issue. Shop charged me $36 to replace these and problem was solved. No more shuttering or stalling at stop lights when AC on. Check the easy stuff. Could be the pcv valve.