Occasionally, the engine idle will start to fluctuate, sometimes to the point that the engine swings from very low RPM's to much higher RPM's, then low again, ultimately stalling. Although several things can cause this, most often, it is the result of a malfunctioning IAC. The IAC allows air to bypass the throttle plate. The air passages and the armature (or valve) within the IAC can and do become contaminated with debris and particulate causing erratic operation, or failure to work at all.
Often, the "from the book" method of correction is to replace the IAC, but in most instances, a simple cleaning ~may~ return the IAC to fully operational status. I have done this many times over the years with great success.
You will need a screwdriver and a can of ordinary carburetor cleaner. I ~have~ used WD-40 in the past with somewhat satisfactory results.
It is necessary to remove the fresh air intake tube to gain access to the IAC's inlet port. It is not necessary to remove the IAC from the throttle body. The electrical connector must remain connected.
Start by loosening the clamp at the throttle body....
Grasping the tube with your hands, move the tube up and down while pulling it away from the throttle body until it is free.
Repeat the process at the air filter box and set the fresh air tube aside.
Looking into the throttle body, you will find the throttle plate closed and a "port" on the froward facing interior of the throttle body.
This is the intake port for the IAC. The discharge port is on the other side of the throttle plate. Manifold vacuum draws air through the IAC, past the closed throttle plate.
Install the straw provided with the carburetor cleaner into the nozzle of the can and insert the straw into the intake port of the IAC within the throttle body.
Spray a one second spray of carburetor cleaner into the port and remove the straw from the port.
Start the engine. It will start hard and stumble, then begin to run smoothly as the carburetor cleaner is burned off.
Gently change the engine speed using your finger on the end of the throttle linkage, slowly working the engine speed up and down, allowing it to come to momentary idle during each cycle.
It takes very little movement to accelerate the engine. You can view the throttle plate opening and closing while doing this.
You should repeat the process several times to assure that the cleaner has washed the particulate through the IAC. After initial treatment, you can also spray small amounts of carburetor cleaner into the port ~while~ the engine is running, but it will be necessary to operate the throttle as shown above during this process, as the engine will want to stall. I prefer this method as the IAC operates during this process, helping to dislodge particulate. SMALL doses of carburetor cleaner must be applied with this method as the engine will easily stall.
Once done, re-install the fresh air tube and check for stable idle.
If this does not correct the idle issue, then a replacement IAC must be installed or the idle issue must be located elsewhere.
I use this process as preventative maintenance whenever possible, practical or I am experiencing an erratic idle issue.
Art
