Auto Repair Q&A



Cooling System










Auto Repair Products

IAC Valve Idle Surge Fixes

IAC Valve

Erratic idle and idle surges are often due to problems with the idle speed control valve (aka idle air control valve). An idle speed that is not steady (erratic) or that surges (suddenly increases for short periods) is often varnish deposits on the idle air control (IAC) valve. This is a relatively simple fix.

Cleaning the IAC Without Removal

Disconnect the air intake ducts from the throttle body to gain access to the IAC, if required. Start the engine and throttle the idle RPM to between 1,000 and 1,500. This creates the suction into the IAC that you'll need.

Spray throttle cleaner or engine cleaner into the throat of the throttle body towards the idle air bypass port, which is usually on one side or at the top of the throttle body opening. You want 10-12 seconds of continuous spray of cleaner to get into that area and do its work.

As soon as you're done spraying, shut off the engine. Let the cleaner soak into the passages for three or four minutes.

Restart the engine and do the cleaning process again, with RPM at 1,000-1,500 and with spray entering for 10+ seconds.

Turn off the engine and reattach intake ducts. Restart the engine and hold RPM as close to 2,000 as you can. Do this until the exhaust stops emitting white smoke, usually a minute or two.

Removing the IAC for Cleaning

If the idle surge has not been completely fixed with the above cleaning process, you may need to remove and thoroughly clean, or even replace, the idle air control instead.

Remove whatever is required to gain access to the IAC, usually the ductwork as above. Then remove the IAC by unplugging its control wiring (most IACs have a coupling right at their base) and removing the screws that hold the IAC in place. There are usually two or three and they are usually on the "top" or upward-facing portion of the IAC opposite of where it attaches to the manifold.

Once the IAC unit is off the car, clean its surface that attaches to the vehicle thoroughly, then use engine or throttle cleaner directly into the IAC's ports. do it in five or six-second blasts, then let it soak for three or four minutes and repeat. Three cycles will usually thoroughly coat and break up any varnish and carbon that may be blocking the valve.

Reattach to the vehicle, re-install the ductwork, and start the engine. Run at around 2,000 RPM until white smoke stops emitting from the exhaust; usually two or three minutes.

If this does not solve the idle surge or erratic idle problem, then you may need to replace the IAC instead.