2004 Silverado 5.3L Vin T Idles low

[DDGLDO]

I am the proud owner of a 2004 Silverado Crew Cab truck with 210276 miles on the clock and no check in light or trouble codes...  truck has been really great since I bought it new.  I now have a problem where I get an extremely rough idle after driving at highway speeds and stopping at a ramp light when exiting.  I am worried because a few times the truck backfired and nearly died on me.  I have replaced the O2 sensors (All of them)at the start of these issues as they were original to the truck. I have also cleaned the throttle body and replaced the spark plugs.  Using my data logger I can see that the throttle is at 4 to 5% at idle in the driveway at 525-560 rpms (fluctuating rapidly).  I have looked for vacuum leaks and found none.  I am thinking that my Throttle Position Sensor may be about to give up the ghost.  What do you guys think based off of the information I have provided here?  If you need more let me know please. 

 

List of new parts installed in order before and after trouble started:

battery (Just before issues started)

O2 sensors (all after issues started)

Plugs (After)

Plug wires inspected, no apparent damage and less than 1 year old

Throttle body removed and cleaned on the bench (After and last thing I have done before this post).

 

 

Thank you in advance!

 

Edited January 24, 2022 by DDGLDO
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[richard wysong]

try doing the idle relearn procedure. when you changed the bat you lost memory. it sometimes has to be done after a throttle clean as well. also try cleaning the idle air control and make sure the pintle moves. did you check with a scan tool or just a code reader?

[richard wysong]

as it all started when you changed the bat make sure any wiring, grounds in that area didn't get damaged

[DDGLDO]

Richard,

Thank you for the reply!  I used my handheld scanner to check for the DTCs.  I did disconnect the battery again, let the truck idle for 5 minutes, turned it off for about a minute and then started it again to idle for another five.  After turning it off for about 20 minutes (Long enough to change my pants and grab my wallet) I took it on a thirty mile drive at highway speeds.  As for the IAC, I don't think my truck has that...   I thought the problem may have been resolved until I was on my way home and noticed it doing it again.  Call me crazy but I think it even did while under acceleration up a hill.  

 

I will go out and take a closer look for anything amiss around the battery and let you know if there is anything going on there.

 

Thanks again!

Edited January 25, 2022 by DDGLDO
Answered question about IAC

[richard wysong]

it has an IAC somewhere in the area of the throttle. thats how the pcm controls idle speed. has a 3 wire connector and 2 screws holding it to the throttle body. the way it works is it screws the pintle in and out to control basicly a vacuum leak that raises and lowers the rpm to the pcm command. they get stuck occasionly and may not set a code. if your scanner does data you should see the counts start high when you start it and slowly decrease. when you take it out to clean it and the passages it sits in you will probably find it fully extended, clean it and then screw/push the pintle in before reinstalling. when you start it the idle should be higher than normal but quickly decrease, if it doesn't its probably NG

[richard wysong]

there was a post a while ago with the same symptoms and cleaning it cured it

[CamGTP]

Trucks with electronic throttle bodies do not have an IAC. The idle it controlled by the blade itself.

 

Off hand I don't know what the throttle percent should be at idle but I thought it should be at 5% or more.

 

A throttle relearn is still a good idea. I'd double check fuel pressure at idle as well. Clean the MAF too.

 

And see what your fuel trims are doing while at idle and driving. Lots of negative trims means it's pulling fuel and positive trims means it's having to add in fuel to make it happy.

[richard wysong]

maybe some1 can take a pic of it and post it to show you

 

 

 

 

[richard wysong]

learn something new everyday. thank you for correcting me. what year did they start electronic throttle control?

[CamGTP]

Depends on what trim you have.

They used it in as early as 2001 in the trucks like the Denali. Some Silverado/Sierra's have it in 2001-2002 as well if they have the advanced traction control system in them but not many had that. They went full time drive by wire in 2003 with the 4.8/5.3/6.0 in all trucks. The 4.3 stayed cable driven for a few years yet and same with the commercial vans like the express.

 

Corvettes have been DBW since 1997.

[richard wysong]

thanks , good to know

[DDGLDO]

2 hours ago, CamGTP said:

Trucks with electronic throttle bodies do not have an IAC. The idle it controlled by the blade itself.

 

Off hand I don't know what the throttle percent should be at idle but I thought it should be at 5% or more.

 

A throttle relearn is still a good idea. I'd double check fuel pressure at idle as well. Clean the MAF too.

 

And see what your fuel trims are doing while at idle and driving. Lots of negative trims means it's pulling fuel and positive trims means it's having to add in fuel to make it happy.

CamGTP,

Thanks for the info!  I will take a look on my way to work tomorrow how the fuel trim looks.  Just at idle both were at 2.  Just redid the throttle relearn tonight.  

 

Thanks again!

[richard wysong]

i have had to do the relearn a couple times for it to take before

[dna9656]

Ya know Richard, I don't understand why it takes repeated tries to get the ECM to relearn. It's a bunch of chips fercryinoutloud!

Edited January 28, 2022 by dna9656

[richard wysong]

ya got me, could be it doesn't see all the data parameters on the first pass? Im not saying everytime it has to be done twice but from experience if it doesn't fix it the first time try it again before moving up the tree