change page: < back next > home

Question I have an 88 Chevy Astro with the 4.3L engine. The idle is too high. After checking for vacuum leaks I checked the idle air control valve. The computer is sending 12 volts down two of the four wires at the connector, which changes polarity in an attempt to drive the plunger in and out. Upon removing the IAC valve I used a sensor tester and a small 12 volt battery to see if it would work. The plunger will not move in or out so I assumed it was bad. I tested the new one to make sure I had the test procedure correct. It does not move either. My parts house lent me another one as they agreed it was being tested correctly. It doesn't operate using this test method. I am aware that the other two wires are for sending the position signal to the computor when at 40 mph or above the speed sensor causes the plungers to travel to the extended closed position so it can reset the 0 position. When I test the original and replacement units there is continuity from pins A to B and for C to D. What am I doing wrong? What is the correct way to bench test this IAC valve? Also what would be the next item most likely to have failed? Since the voltage signal changes back and forth I assumed the computor and everything was working OK. I am also working on a 90 Toyota Camry with the 4 cylinder 2000 cc 16 valve engine. The customer has it in to other shops before with the same problem. When it is cold and there is moisture/dew in the air the car will runs rough and die at idle until it has run for 5 to 10 minutes. At speed it is OK. There is no moisture in the distributor cap no loose connection or corroded ones that we can find. It does not act up when cold, only when there is moisture. Thanks for any advice you can send my way. Sincrely, Ken

Reply The correct way to test your IAC valve is with an IAC testing tool which will properly switch voltage to the valve. You may want to ensure that your testing tool is not defective. The voltage from the computer must be tested with a special noid light which correctly tests the change in polarity. Often, a binding IAC valve can ruin a vehicle computer by drawing too much current. Correctly test the IAC valve and computer, replace components as needed, and be sure to check minimum air rate. Incorrect air rate adjustment and/or vacuum leaks can cause premature IAC valve failure. On your Camry, I would suggest inspecting everything in the secondary ignition system including distributor cap and rotor, spark plug wires, plugs, and ignition coil. Checking these items with an oscilloscope and a spray bottle filled with water should turn up the problem. Angelo Silverado Auto Service