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Have a 06 Grand Caravan 3.8L that suddenly quit and would start back up easily enough, but one had to keep foot on the gas to keep it going.
I pulled two codes:
P0123-throttle postion sensor 1 high
P0508-IAC valve sensor circuit low/undercurrentSo far I have removed the IAC and cleaned it with throttle body cleaner, cleaned throttle body out as well with the spray, installed new EGR since it got mangled trying to remove it for cleaning. Removed the TPS connector and with key on, took measurements and I am getting a reference voltage proper ( almost 5 volts). I then back probed the connector once it was plugged back in and again things checked out, the reference lead was varying between .7 and 4.7 volts as I manually moved the throttle plate.
I had switched out the IAC with a used one, from an engine that had been running before being parked, but it made no change. Just to be on safe side I installed new TPS and IAC as well, to rule them completely out.
I’m thinking only thing to tackle now would be to change the fuel pump? Possibly clogged pickup filter?
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Unless you have diagnosed an issue with the fuel pump, I would say hold off on that… You have two known codes with some electronic issue… Fix those first before you look for a fuel delivery issue (and if you are going down this road, it is best to get the fuel pressure tested before you replace a fuel pump)
Has anything been done to the vehicle recently?
May want to inspect the wiring and look for common grounds on that circuit.
I would hook it up to a scanner and observe what the PCM is being told about the TPS position… You may find with the engine running and revving the engine while looking at the scanner when the error is occurring..
-Karl
This problem occurred the other day during big rain storm, so I had thought maybe some kind of damp/wetness had caused it, but it has since dried, so thats out. Just basic maintenance things been done lately to this van, nothing in the electrical side of things. So keep it running and try and record a datastream maybe?
Yes, if possible run the vehicle and observe the TPS readings… You may consider erasing the codes (they will pop up again if the issue keeps occurring) and hook a scan tool up and observe the TPS reading while revving and if possible, while driving… Perhaps there is a dead spot in the TPS or something else… Look for an out of whack reading on the TPS when revving and driving…
Maybe the TPS issue is related to the IAC issue, maybe not.. But as I said earlier, I would inspect the wiring for any issues…
-Karl
Just ran it with the scanner connected and watched the datastream, with TPS info at the top. (had cleared all DTC’s first) TPS voltage stayed at zero as I held my foot on gas pedal to maintain approx 1000 RPM, pretty sure there should have been some sort of reading there. TPS % showed varying amounts as I changed position of throttle, but nothing changed for TPS voltage…
It immediately ran a code P0508
The P0508 code you’re getting is an IAC short to ground or battery voltage code.
Since you both cleaned and replaced the IAC with one you know to be good I’d take a look at the wiring connecting to the IAC.As far as the TPS voltage issue maybe your scanner just can’t interpret that data correctly and is showing 0 volts. The signal voltage seemed correct.
I am using an OTC Genysis with 4.0 on it. I just unplugged the IAC connector to see if any difference…there was none. Thought maybe if it was shorting to ground by disconnecting it, might do something.
Something with the IAC and/or its circuit is suspect… Have you checked the fuses yet? Maybe a blown fuse…
-Karl
[quote=”Black_Blade” post=104822]I just unplugged the IAC connector to see if any difference…there was none.[/quote]
Ok so it’s pretty obvious that the IAC is not working properly than. If the IAC was working properly and you unplugged it you would have noticed a change.I agree with Karl.
“adjusted the idle screw” was the note left for me this morning and it has apparently fixed this problem. I had left a message for an retired mechanic I knew, and he had came in and looked at it last night.
I wasn’t aware there was an idle adjustment screw anywhere…that idle was taken care of by the computer via IAC etc… :unsure:
Glad you found the problem. Thanks for the update. In the future if you can’t see a TPS reading then I would ignore the IAC. The computer gets info from the TPS to activate the IAC. If you have bad TPS readings, you’re IAC will not be able to function properly. In summary, if you have those 2 codes, start with the TPS and solve that first. In this case the TPS was solved with an apparent idle adjustment.
Thanks for the updates and for using the ETCG forum.
Thanks for the reply Eric, great vids and site btw, it was my understanding (still learning) that the idle screw on this model was factory set and really not meant to be tampered with and if you had idle issues, it would be the fault of some component or fault in wiring of the TPS circuit. Would changing the factory preset be just a bandaid fix for this sort of thing?
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