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It seems like the idle air controller is just opening and closing at random for no reason even going down the road. It will not idle steady very long, for a minute or two it might idle steady around 800 rpm but a lot of the time it's just moving randomly between 500 rpm and about 1800. some times it will idle down to around 650-750 but not very often and sometimes when it does it just dies when you hit the throttle, doesn't even try to pick up, it just dies. not all that often but does happen.
I don't really think it is the iac, I put on a new one and it didn't make any difference. what should I look at.
new parts:
cap and rotor
plug and wires
pip sensor
temp sensor, for ecm
ecm
ignition switch
I would get an analog volt meter, so you can pull engine codes. There's a thread somewhere on this forum on how to do that.
Then, one likely contributor to a searching idle, is the Throttle Position Sensor. They're best tested using an analog meter, because during the test, you'll be able to see erratic needle movements, if the TPS is faulty.
How are your vacuum lines? On these trucks, it's not that difficult to replace them with 5/32" hose and eliminate any leaks. The Idle Air Control could be trying to compensate for vacuum leaks.
Jumper the green dots and set your volt meter up between battery positive and the blue dot, then count sweeps of the needle, in place of "check engine" light flashes.
You'll need to have an extension for your tester lead to the battery positive, so you can route it over to the battery with enough slack not to get it tangled up in anything during the key on engine running part of the test.
some how I forgot to mention that the tps is new and does test good.
I get codes:
67- Park/neutral circuit fault - pnp
33- egr did not open/respond during test of if memory code, did not open intermittently
44- air system inoperative - air injection
I have found only one vacuum leak and its is from the egr not sealing completely. smog system has been deleted. I'm not to worried about the egr code everything in that system tests good and it still throws a code for it, so I'm just going to ignore it unless it causes bigger problem. but the egr issue has been happening for a while, much longer than that issue.
It doesn't only happen at idle is the strange thing it evens happens going down the road. could the map have anything to do with it?
It seems like the idle air controller is just opening and closing at random for no reason even going down the road. It will not idle steady very long, for a minute or two it might idle steady around 800 rpm but a lot of the time it's just moving randomly between 500 rpm and about 1800. some times it will idle down to around 650-750 but not very often
If you look through threads I've posted, you will find this exact issue, I would just be sitting there, and the IAC would slam open for no reason, it made shifting hard, had to burn the clutch up. It wouldn't idle properly for the life of me.
Test it before you replace it, but I suspect your TPS is cooked. Don't get the cheap one, they fail, and fast (ask me how I know). Don't lose the little spacer that keeps the TPS aligned, that caused issues for me as well.
haven't fixed the egr sealing issue, but it a minor leak and never caused any issues before.
When your truck was doing this did your tps ever test bad?
my tps has had a high idle voltage since i put it on at just a hair over 1 volt but again never has cause much issue.
A TPS can fail in multiple ways, mine was a low signal (code 63) which caused it to behave erratically, it also acted up before displaying a code.
This would cause issues, voltage needs to be ~0.5v-0.9v at idle, over 1v will confuse the computer. Perhaps your TB screw has been messed with in the past? Also make sure the butterflies aren't sticking.
I replaced the tps because, of a code 23- throttle sensor out of range or throttle set too high - tps The tps will not go below a volt at all. I should have adjusted the throttle stop screw before i put a new tps on. when I backed it off a bit the code went away and it idle OK for a while. The idle screw had been run all the way in so the engine would idle with 2 dead cylinders and a couple more that were iffy, of coarse that's been fixed now.
i measured voltage at the tps with the engine running and I never saw the voltage change when it open the iac, but that may not mean very much. It's also not impossible it read wrong for to short a time for the needle to move on my meter.
I replaced the tps because, of a code 23- throttle sensor out of range or throttle set too high - tps The tps will not go below a volt at all. I should have adjusted the throttle stop screw before i put a new tps on. when I backed it off a bit the code went away and it idle OK for a while. The idle screw had been run all the way in so the engine would idle with 2 dead cylinders and a couple more that were iffy, of coarse that's been fixed now.
i measured voltage at the tps with the engine running and I never saw the voltage change when it open the iac, but that may not mean very much. It's also not impossible it read wrong for to short a time for the needle to move on my meter.
Throttle stop screw all the way in? Yeah that would explain it
The TPS won't change voltage because the PCM is looking at that voltage, and determining how much to open the IAC. It needs to be steady in any throttle position.
You should disconnect your battery for a while so the truck can relearn with the throttle in the correct position. (~500 rpm with IAC unplugged)
the stop screw has been back out for a good while now
I was reading the same voltage the pcm sees, it didn't seem to move when the idle messed up but it may have changed for such a short time the needle on my meter never move. I guess the high voltage at idle doesn't help either.
also how is the iac supposed to act just off idle, it's hard to go real slow because it seems to fully open just off idle. this was before it start the random iac behavior.
The problem didn't seem as bad with the old pcm, but there is a reason i replaced it. before it got to bad to drive it had a habbit of not catching it when it returned to idle and i had the screw set a bit low, so it wouldn't idle without the iac. And since they aren't the exact same ecm I guess it is also possible the new one is more sensitive to the tps voltage, or it's just a coincidence.
probably going to order a tps at Napa tomorrow.
Well, I don't believe it is the tps. The new one actually reads the proper voltage. I reset the ecm when I installed the tps, the issue didn't show back up immediately but as the ecm is relearning it's steadily coming back. Which it has done before, last time the ecm was reset it took a bit for the issue to come back completely.
The iac connector came apart a while ago and I don't know for sure the wires ended up on the correct pins, Is there any way someone could find out with color wire goes to which pin.
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