IAC problems....new PCM?
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IAC problems....new PCM?
So here is the story....
I gave my son a 99 1500 with 79k miles a while back, he is a Marine down in San Diego. It was sitting for a bit and the battery died. Battery was replaced, and I am sure the PCM was not reset, as some have said needs to be done. Shortly there after it would not run, just kept dying. A friend told him it was the IAC so they replaced it. Mind you these are not mechanical guys in the least. That was a few months ago. He came home last week and complained that the idle was about 1500 in park but ok in drive. I looked it over and found the new IAC was never plugged in. I plugged it in and idle started to come down and settled about 600 rpm, drove it and all seemed good.
Went to start it later and it would barely start, then die. Bought a new IAC and went to put it in, but thought I would just adjust the older newer one to the position of the new one. Put it back in and it idled about 1500 and then came down and settled about 600 again. but later on it would not start again. The IAC was moving so I assume it is good. Now it seems to not work at all. By adjusting I mean I held the spring and spun the plunger, spin freely so it isn't binding. Tired resetting PCM with battery disconnected and turning on ignition with gas pedal to the floor.
I am getting a P0505 fault, I unplugged the IAC, still get fault after clearing it, cleared it again and I get the fault just turning the ignition on and not even starting it. I checked the harness for continuity and shorts between wires and it all looked good. We had returned the new IAC so I did not try it, but I think faulting without it plugged in eliminates the IAC.
The gas gauge stopped working while I was testing all of this, would read empty on one start, then would read full on the next start. Could be coincidence but who knows.
I just want to make sure it is the PCM before I spend $250.
I gave my son a 99 1500 with 79k miles a while back, he is a Marine down in San Diego. It was sitting for a bit and the battery died. Battery was replaced, and I am sure the PCM was not reset, as some have said needs to be done. Shortly there after it would not run, just kept dying. A friend told him it was the IAC so they replaced it. Mind you these are not mechanical guys in the least. That was a few months ago. He came home last week and complained that the idle was about 1500 in park but ok in drive. I looked it over and found the new IAC was never plugged in. I plugged it in and idle started to come down and settled about 600 rpm, drove it and all seemed good.
Went to start it later and it would barely start, then die. Bought a new IAC and went to put it in, but thought I would just adjust the older newer one to the position of the new one. Put it back in and it idled about 1500 and then came down and settled about 600 again. but later on it would not start again. The IAC was moving so I assume it is good. Now it seems to not work at all. By adjusting I mean I held the spring and spun the plunger, spin freely so it isn't binding. Tired resetting PCM with battery disconnected and turning on ignition with gas pedal to the floor.
I am getting a P0505 fault, I unplugged the IAC, still get fault after clearing it, cleared it again and I get the fault just turning the ignition on and not even starting it. I checked the harness for continuity and shorts between wires and it all looked good. We had returned the new IAC so I did not try it, but I think faulting without it plugged in eliminates the IAC.
The gas gauge stopped working while I was testing all of this, would read empty on one start, then would read full on the next start. Could be coincidence but who knows.
I just want to make sure it is the PCM before I spend $250.
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Joined: Apr 2010
Posts: 87,394
Likes: 4,213
From: Clayton MI
With everything hooked up, disconnect the battery. Turn on the headlights, and leave it for about 30 seconds. Turn the headlights off, hook the battery back up. Turn the ignition to On, (not start) count to ten, THEN start the engine. Don't touch the gas pedal while doing this. That *should* reset the PCM, so it will relearn the zero values for the various sensors. If the 505 code comes back right way, then yeah, you have another problem somewhere.
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With everything hooked up, disconnect the battery. Turn on the headlights, and leave it for about 30 seconds. Turn the headlights off, hook the battery back up. Turn the ignition to On, (not start) count to ten, THEN start the engine. Don't touch the gas pedal while doing this. That *should* reset the PCM, so it will relearn the zero values for the various sensors. If the 505 code comes back right way, then yeah, you have another problem somewhere.
Captain
Joined: Jan 2016
Posts: 593
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From: Shawnee, KS
With everything hooked up, disconnect the battery. Turn on the headlights, and leave it for about 30 seconds. Turn the headlights off, hook the battery back up. Turn the ignition to On, (not start) count to ten, THEN start the engine. Don't touch the gas pedal while doing this. That *should* reset the PCM, so it will relearn the zero values for the various sensors. If the 505 code comes back right way, then yeah, you have another problem somewhere.
1999 Ram 2500
Administrator
Joined: Apr 2010
Posts: 87,394
Likes: 4,213
From: Clayton MI
It's *my* standard procedure. 
Makes sure the PCM forgets everything it ever knew. It then relearns the sensors. Might clear up your code, might not. (it *should*) If the code comes back, we can move on to the next step.
Makes sure the PCM forgets everything it ever knew. It then relearns the sensors. Might clear up your code, might not. (it *should*) If the code comes back, we can move on to the next step.
Administrator
Joined: Apr 2010
Posts: 87,394
Likes: 4,213
From: Clayton MI
