Steering wheel shake when A/C or front defroster is turn on

Tiny
MBUB1999
  • MEMBER
  • 2004 FORD FREESTAR
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
A noticeable vibration of steering wheel and increase in RPMs can be felt when A/C or front defroster is turn on at idle. The issue come and go when the car is on drive or idle but less noticeable when in drive. Motor mounts are good. Changed out with new throttle sensor, EGR valve, idle control valves, spark plugs, spark plug wire and coil. The car computer seems to be dry but did not take apart and inspect the inside. The repair shop think it might be the car computer. The repair shop has rule out the A/C compressor. Could it be the car computer or something else?
Monday, September 27th, 2021 AT 8:48 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
Hi,

When the A/C or defroster are turned on, the compressor is engaged. That is placing an added load on the engine. The vehicle has what is called an idle air control valve. This system is designed to increase the idle speed and compensate for the added load.

Pay attention to the engine speed when you turn the AC on and off. Pay attention if the engine speed (idle speed) changes a lot when it is on.

If it drops, try servicing the IAC. Here is a link that explains how it's done.

https://www.2carpros.com/articles/idle-air-control-valve-service

I attached a pic below of the IAC's location. It will be mounted on the throttle body.

Let me know if this helps.

Take care,

Joe

See pic below.
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Monday, September 27th, 2021 AT 8:13 PM
Tiny
MBUB1999
  • MEMBER
  • 2 POSTS
As mentioned in post, the IAC have been replace with new part - no change.
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Wednesday, September 29th, 2021 AT 6:36 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
Hi,

Sorry about that. I missed it. Can you tell me what the engine idle speed is? Also, have you checked for engine vacuum leaks?

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

The attached pic below indicates the manufacturer's idle speed specs. Is that approximately where the vehicle idles?

Pic 2 shows the PCV valve and PCV valve tube. Check closely for leaks in the tube and confirm the valve is good.

Joe
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Wednesday, September 29th, 2021 AT 7:07 PM

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