I figured out how to start the new thread. sorry about putting it on this one. The code P0505 (Idle Air Control System) Like I put in that other post, The idle is running between say 800 and 1200. Its noticeable to me, but not others. It runs really smooth though. Im gonna change the crank position sensor ( I was thinking thats what you meant by CPS, but you could have been referring to the cam position sensor. I need to figure this out and get it fixed because I want to say when they plug in during inspection, it will still give them that code if I havent put 500 miles on it after getting the light to go off. All suggestions are much appreciated

 

"failing crank position sensor" is what I was talking about in the previous line, so CPS is Crank Position Sensor.

CPS (Crank Position Sensor) deals with timing... the cam position sensor (which I believe is called the Distributor Pickup Coil) just says what cylinder.

As the CPS ages, it becomes less accurate, so therefore the timing is less accurate... it could be running more or less advance than it thinks it is... this is the contributor to the symptoms noted earlier... as it deteriorates further, the random misses become more common.

 

Another member had issues with intermittent/weak spark on just a couple cylinders. The PCM would still fire the coil, but, the spark wasn't what it should be. Replacing his CPS solved the issue.

Quite frankly, I was surprised that the sensor could have that kind of failure mode. Considering that the crank sensor is just telling the PCM that some cylinder or other as approaching firing position, I always figgered it to be an 'all or nothing' type of affair, which evidently, isn't really the case.

 

My theory is; as the sensor ages, the active sense zone gets wider, so the trigger point can fall in a bigger window of degrees... when the PCM sees the CPS it is under the impression that the crank is at x° of rotation, it adds/subtracts based on the other engine sensor parameters and says fire now... if x° was rally x+° (or x-°), the whole calculation is off and you don't get spark when you wanted.

Unlike other deteriorating/failing sensors that will cause a situation that some other sensor will ultimately see as something being wrong, and the PCM will try to correct for, the PCM is oblivious to a CPS error.