stumbling at idle 2003 4.8....TPS sensor problems?

[JeRM82]

I have a friend who just bought a 120K mile 2003 silverado with a 4.8 in it. It has a problem when it's idling where it almost dies when you put the trans into reverse, and it you hold the brake and BARLEY toutch the gas pedal enough to get a response....it stumbles down to 400rpm, and JUST about dies....but comes back to idle....my friend says that it HAS dies on him like that before....but we are still trying to figure out EXACTLY the same conditions other than what I just said....I used my Predator and scanned the Throttle Position at idle, and its at 15% while at IDLE......and "arbritrary (I think) throttle position" is at the same, or just as high at 14.xxx% at idle.....Is that a BAD Electronic Throttle control or Throttle position sensor?
I scanned my 07 5.3 truck and at idle and durring the same put into reverse conditions my truck sits at only 5%, and bumps up to 6% or so when I put it into reverse, or tap the gas like I was doing with his truck....BOTH of our trucks idle at around 500rpms or so....his almost dies and doesnt seem to be compensating for the load put onto the motor by putting the truck into reverse.....
It SEEMS like its a TPS sensor or that electronic throttle control because the truck at IDLE sits at 15% Throttle position......its like THREE times as high as mine is...and it STILL idles at 500 rpm's......anyone ever run into this before? I am going to do the idle reset from the sticky above this thread and clean out the Idle Control Valve thing...ha ha....but while I was doing that I thought I would get some input from you guys and what you all think about this.....

We JUST put new plugs and wires on the truck because they needed to be changed, we did it just to replace them and get the truck running on some fresh spark, and the plugs were pretty old....didn't change the almost stalling situation....LOL....

[RedHeartbeat]

could be a bad MAP or dirty MAF. Usually a vacuum leak you'd have a low TPS reading and idling high so I'd rule that one out. Start out by cleaning the MAF with some spray cleaner made specifically for MAF sensors, especially if his truck has a K&N or similar oil-type aircleaner.

[JeRM82]

hmmm....could it be the ACTUAL electronic throttle control going bad? I've never had to mess with a truck that had didnt have a cable for a throttle body.....we're going to clean out that Idle control valve today....I just gotta find it...The truck MIGHT have had a K&N on it....I honestly don't know and I dont think he does either....the truck has the stock stuff on it with a paper filter....I'll grab some of that MAF cleaner on the way over there....
The thing that was making me thinkg about the throttle control or that throttle position sensor is the fact that the truck has that 15% reading at idle and my truck sits at only 5%.....his truck is an 03 with a 4.8.....and mine is an 07 with a 5.3 in it.....I was gonna see if someone who has an electronic throttle bodied 4.8 truck could just check thier throttle position percentage durring idle and what it jumps to when the truck gets put into reverse.....just as a reference.......are those numbers NORMAL? His reads THREE times what mine does at idle....but the trucks BOTH idle at the SAME RPM.....kinda wacky to me....but maybe its an apples to oranges comparison because my truck is a 5.3 and an 07....even though mine is a classic....

Can I actually take a look at that MAP sensor with the predetor hand held? I've never had to troubleshoot one of those....any tips? The truck idles by itself just fine...its just when it has an actual LOAD on it like when it put into reverse or when you BARELY toutch the gas pedal enough to get it to read that it stumbles like that....and comes back to an idle...

[RedHeartbeat]

The IAC is a function of the throttle blade. The PCM will hold the blades open to where it needs to get the correct AFR at idle. Turn the engine off and look at the blade, it should be closed completely. If not, get some throttle body cleaner and clean it up. You may have to take it off to get it really clean.

[Madd Maxx]

Yup - give the throttle body a good cleaning. It's a common problem.

[JeRM82]

So can I clean it with just regular old brake clean or do I need to use the MAF cleaner? I just don't wanna jack up that electronic throttle control....never had to mess with it....and it LOOKS expensive....ha ha...know what I mean?

[RedHeartbeat]

use throttle body cleaner. They sell that stuff ready to spray. You may have to scrub it a little if it's too caked up.

[JeRM82]

Well...this thing is getting pretty damn wacky...ha ha...looks like a SHADY dealership sold my friend the truck...pulled the cover on the fuse box and found a wire just JAMMED under one of the fuses for some reason..it seems to have been pulling power for the radio, pulled the wire out...radio goes dead....and then the check engine light comes on after 5minutes of driving...circuits a and b for the tps are bad and there is no communication to the computer from the tps....JEEZE..WHAT A MESS...Thank you guys for all of your help! Haven't replaced the sensor yet...but when we do I'll post up more info...

[keniff]

my phone will double post for me lol
anyway how long has he owned the truck? he should take it back to the dealer under the lemon law..im not too sure of it but i know id be extre ely mad if i bought a poo truck.

[Madd Maxx]

It's doubtful the dealer is even aware of the issue. Most dealers do little more than steam-clean the engine, vacuum the interior, and put that nasty black stuff on the tires before putting a used vehicle on the lot.