This happened once last year and tonight again; while driving a sustained highway speed (70 or so mph), the engine feels like it is lugging on deceleration. The tachometer however stays at around 1500 rpm. Once the car slows down, the tach remains at 1500, idling too high, and then the revs start pulsating up and down between 1000 and 2000 rpm. I turned the car off, let it sit for about 30 seconds, restarted it, and the problem went away. This happened last year with a different idle air control valve. I thought that the replacement idle air control valve was defective and that putting the original back in solved the problem, but tonight the same symptoms occurred with the original. I also cleaned the throttle body last year after the problem occurred and the idle control valve seat. Should I do this again?
HI Larry, I’ll do that, and a clean out too. Neither the check engine or transmission light came on during this episode. Ironically it happened in the same spot on the same road as last year (NJ Turnpike, heading south).
Try pulling and clean out the WHITE GUNK out of that rubber hose on middle left of the valve cover. Apparently that might be where the PVC SHOULD BE BUT NOT!!!??? USE A SMALLER FLEXABLE (aquarium hose) and blow the funk into the oil pan!!! Let us know if that help!?
I had a similar drivability issue - but on coast-down when the RPM reached 1000 the ‘black box’ would blip the throttle and the RPM would increase to 1500, drop down, blip up, etc. Upon braking to a stop the idle may be at 650 (good) or it may dip to 500 or settle at 850 (bad). This all developed after I had replaced the idle air control valve, cleaned the seat, cleaned the throttle body, cleaned (flushed out) the throttle position sensor (TPS), and checked the TPS setting (no adjustment required). For once I remembered to check the simple things first, and found the throttle plate gap was less than the .002 (two thousandths) spec. I adjusted the throttle plate to a loose .002, re-adjusted the idle air control valve, and drivability seems to be back to normal. During the initial test drive the idle speed at stop did not want to come down to 650, but stayed around 750 whilst in drive, and around 950 (rather than 800) in park. I let the ol’ girl sleep on it and that seems to have restored some normalcy as during my drive this morning there was still no RPM fluctuation on coast-down and the idle speed has settled out at 650 while stopped in drive.