2003 4.3 Auto, Strange Idle Issue

[Spiney Norman]

Is there a link between the transmission being in a drive gear and engine idle speed? Does the trans send a signal to the PCM that raises the idle? My truck is an S10 but this forum gets much more traffic than the S10 room does so I'm posting here. Sorry. Truck has 137k miles, I've kept up on maintenance to include replacing the F.I. spider a couple months ago which fixed a "hard to start" issue. I cant find any vac leaks, TPS and IAC valve are new too. The truck knows when it's in drive or reverse and the idle speed rises to about 1400rpm. Sometimes, when I'm driving, I'll pull it into neutral, the rpm's will sort of cycle, 1000, 1500, 2000, 1500, 1000. Strange.

 

Yes, I've searched here and on the net in general. Everyone says throw a TPS or IAC at it.

 

I bought one of those bluetooth dongles on ebay but to be honest, I dont know much about the diagnostic data it gives me.

 

I'm wondering if it's a transmission or PCM issue and not a fuel system issue at all. Really need a little help, any input would be appreciated.

Edited June 29, 2024 by Spiney Norman

[richard wysong]

Any codes? Is the TPS within range throttles closed? The trans selector switch does indeed transmit to the PCM. Have you tried cleaning the throttle plates? has the throttle stop adjustment been messed with? Try doing an idle relearn if all else checks out

[Spiney Norman]

No codes at all. I cleaned the he!! out of the throttle body when I had it off a couple months ago to replace the fuel injector spider. I have not messed with the throttle stop. That's not to say it hasn't been adjusted. The truck was in rough shape when I bought it. It was cheap for a reason.

 

My TPS shows .39% at idle

 

I thought the "idle relearn" was only for the modern fly-by-wire throttle systems? Mine is old school cable operated.

Edited July 1, 2024 by Spiney Norman

[Spiney Norman]

Well I'm all ears if anyone knows what the proper, closed throttle range is supposed to be?

[richard wysong]

idle relearn applies to anything with an IAC

[Spiney Norman]

The truck seems to idle fine, about 600 rpm in park or neutral. The astronomical idle in gear issue remains.

[Spiney Norman]

I enjoy listening to crickets chirp so I'll ask anyway. The idle re-learn for this is 3 minutes at idle, 1 minute off, 3 on again?

 

Acceptable closed TPS idle range?

 

I assume Wysong knows but he's been very busy lately.

[richard wysong]

Sorry I do not know, I would have to look it up same as you.

[Brent R]

If I'm not mistaken that has a drive by cable throttle body correct? If so I believe the TPS should be at 0 because of the IAC solenoid, I could be wrong but I had a 2005 4.3 with a 5 speed for a while and messed around with it quite often.