IAC revisited

IAC is the idle air control valve. This discussion relates to a 1994, 4 cylinder Camry. Seems operation of this valve is a recurring problem. Best information I could find on the Internet was to spray emission control safe carburetor cleaner in the small square orifice at the front/ bottom of the throttle body to restore operation, or replace the valve. Problem manifests as stumbling low idle when first starting up in the morning, that is, the automatic fast idle for the cold engine doesn't engage. If you put it in gear like that, it dies. For the first couple of years, the carburetor cleaner worked fairly well. Remove one hose clamp, short burst of spray, turn the ignition switch on and off a few times, to try to force the valve to move and all would be well for another few months. Then the "cure" started to fade and the problem would recur within a few days. So I ordered a new idle air control valve and throttle body gasket and consulted the Factory Service Manual. The procedure for throttle body removal included procedures for adjustment of the TPS (throttle position sensor), instructions for cleaning with solvent and compressed air, and procedure for calibrating a vacuum diaphragm which controls the butterfly throttle plate. One of the vacuum ports had been at least partially blocked - now cleared, the .012" setting on the TPS was off, and adjusted per spec., and the idle speed at the vacuum diaphragm with the line removed after reassembly required adjustment. I did all of this. Since the old IAC valve was going in the trash, I disassembled it for examination. There is a bimetallic thermostatic coil on one end of the shaft and a round permanent magnet on the other end. The cylindrical part with the port that moves to progressively open or close had a small groove worn in it as if there had been some contamination or binding. All was well for about six months until the rough idle at cold start returned. Finally, the idea presented that there is no lubrication for that valve. Have been using TriFlow aerosol for the electrically powered antenna after seeing this specialty lubricant in a bicycle shop - for use on chains and cables, to lubricate without attracting dirt.

I sprayed a small amount of TriFlow into the IAC valve on the theorythat perhaps that bimetal thermostatic coil is supposed to rotate theIAC valve when cold, and if it sticks slightly, the spring pressure maybe insufficient to move it. The permanent magnet on the other end mustbe part of the computer controlled step motor that adjusts idle speedcontinuously to maintain the target value.Works great. Idle speed when cold is very "fluid", that is, rises justfor an instant then settles slightly and adjusts downward as the enginewarms, just as it should.So perhaps this is the solution for what appears to be a designweakness in an otherwise superbly engineered vehicle - a way to keepthat valve moving smoothly without gumming up or attracting dirt.We shall see.