Low idle in 2001 5.3, can it be adjusted?

[FordBoy33]

Any way to adjust the idle on these Vortec 5.3L V8s, or can it only be adjusted in the PCM? Its a 2001 with only 30000 miles.

I get a lower than expected idle (500), that drops even lower when the a/c clicks on. Occasionally after restarting the engine when its already warm, I get a rough idle until I punch the gas a bit. Then its fine....

Thanks!

[GMMerlin]

Originally Posted by FordBoy33

Any way to adjust the idle on these Vortec 5.3L V8s, or can it only be adjusted in the PCM? Its a 2001 with only 30000 miles.

I get a lower than expected idle (500), that drops even lower when the a/c clicks on. Occasionally after restarting the engine when its already warm, I get a rough idle until I punch the gas a bit. Then its fine....

Thanks!

First, clean the throttle bore..this takes care of most low idle complaints on these vehicles.
There is a GM Technical bulletin addressing your concern..I'll post it tommorow when I get to the shop.
DO NOT adjust anything till you read the bulletin

[FordBoy33]

GmMerlin, any thoughts on whether I should try to remove and clean the IAC valve? That's been recommended to me as well, that it might be sticking and therefore unable to respond quickly when the PCM tells it to adjust prior to the a/c kicking on or other load....

Looks like that IAC valve is on the driver's side of the throttlebody, but torx screws are blocked by the alternator. Ugh. Your solution (remove the plastic air intake tubing and clean the throttle bore with carb cleaner?) sounds easy enough....

Would a handheld OBDII scanner (like the Equus 3100) or OBDII software help in situations like these? Would it show any useful information (about IAC or anything else related to idle) when there's not a "check engine" light lit up?

Thanks.

[GMMerlin]

If you have a throttle cable actuated throlle body, the following bulletin applies.
If you have a "drive by wire" TB then just remove the air duct and clean the TB and blade with a quality choke cleaner and a soft tooth brush.
Removing the IAC is not necessary.
The condition is caused by dirt build up on the TB bore and blade


Increased Accelerator Pedal Effort, Idle Instability (Clean Throttle Body and Adjust Blade) #02-06-04-054B - (03/17/2003)
Table 1: TPS Voltage Chart
Increased Accelerator Pedal Effort, Idle Instability (Clean Throttle Body and Adjust Blade)
1999-2002 Chevrolet Silverado

2000-2002 Chevrolet Suburban, Tahoe

2002 Chevrolet Avalanche

1999-2002 GMC Sierra

2000-2002 GMC Yukon, Yukon XL

with 4.8L or 5.3L V8 Engine (VINs V, T, Z -- RPOs LR4, LM7, L59)

This bulletin is being revised to add condition information. Please discard Corporate Bulletin Number 02-06-04-054A (Section 06-Engine).

Condition
Some customers may comment on an idle instability and/or a higher than expected accelerator pedal effort from the idle position.

Cause
Condition may be caused by deposits in the throttle body bore and on the throttle plate.

Correction

Important
This procedure only applies to cable actuated throttle bodies on the models listed above. This procedure should not be performed on electronically controlled throttle bodies or on any vehicle or engine that is not listed above in the Models section.


Verify that the cause for this condition is not a damaged or binding throttle cable.
Remove the air intake duct. Refer to Air Cleaner Duct Replacement.
Inspect the vehicle for installation of a fixed orifice PCV valve, refer to Corporate Bulletin Number 01-06-01-029B for PCV valve identification. Vehicles undergoing this throttle body procedure MUST use a Fixed Orifice PCV Valve, P/N 12572717.
Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure.
Select the correct plug for the size of the air bypass hole in the throttle body being serviced. Use a 1/8-inch (.125") drill bit to determine which plug to use.
Vehicles built before introduction of the Fixed Orifice PCV Valve will have a 3.75 mm (.150") air bypass hole in the throttle plate. The 1/8-inch drill bit is smaller than the air bypass hole in these throttle bodies and can be inserted into the bypass hole. To plug the air bypass hole in these vehicles requires the yellow plug, P/N 12580749.
Vehicles built after introduction of the Fixed Orifice PCV Valve will have a 2.6 mm (.104") air bypass hole in the throttle plate. The 1/8-inch drill bit is larger than the air bypass hole in these throttle bodies and cannot be inserted into the bypass hole. To plug the air bypass hole in these vehicles requires the red plug, P/N 12581011.




Insert the appropriate plug (1) into the air bypass hole in the throttle plate. Insert the "tail" end of the plug through the throttle plate air bypass hole.



Open the throttle plate to allow access to the tail end of the plug. Pull the tail section to securely position the plug into the air bypass hole and trim excess material (1) from plug.
Turn ignition key to the on position, with engine off.
Use the Tech 2 Scan tool to read initial TPS voltage.

Important
TPS voltage cannot exceed .69 V. If the vehicle has an initial TPS voltage greater than .61 V, replace the Throttle Body Assembly. This part is currently on parts restriction. Contact the General Motors Powertrain Quality Center at 866-654-7654 for assistance.


Using the Tech 2 Scan tool and a T15 driver to rotate the Minimum Air Rate screw, increase TPS voltage by .08 Volts (Refer to TPS Voltage Chart below).
Turn ignition key to the off position. Verify that the accelerator pedal moves freely - Depress the accelerator pedal to the floor and release.
Install the air intake duct. Refer to Air Cleaner Duct Replacement.
Start engine.
Using the Tech 2 scan tool, monitor TPS voltage and verify the TPS voltage is no greater than 0.69V.
Road Test Vehicle.

Important
If an increased accelerator pedal effort condition still exists after performing this bulletin, throttle body replacement may be required. Please contact the General Motors Powertrain Quality Center at 866-654-7654 for assistance, as the throttle body is currently on a parts restriction program.


TPS Voltage Chart Initial TPS Voltage
TPS Voltage After .08 Volt Increase

0.45 V
0.53 V

0.47 V
0.55 V

0.49 V
0.57 V

0.51V
0.59 V

0.53 V
0.61 V

0.55 V
0.63 V

0.57 V
0.65 V

0.59 V
0.67 V

0.61 V
0.69 V


If initial TPS voltage is greater than .61 V Replace Throttle Body Assembly

Parts Information
Part Number
Description
Qty

12580749
Plug, Throttle Plate - Yellow
1

12581011
Plug, Throttle Plate - Red
1


Parts are currently available from GMSPO.

[FordBoy33]

Originally Posted by GmMerlin

If you have a "drive by wire" TB then just remove the air duct and clean the TB and blade with a quality choke cleaner and a soft tooth brush.
Removing the IAC is not necessary.
The condition is caused by dirt build up on the TB bore and blade

Right he is, folks.

I finally had the chance to clean the throttle body this weekend, and the problem with the idle dropping is gone.

Thanks GmMerlin!

[EZRAMACE]

I Too Had A Problem... Every Time I Turned On The A/c Unit. The Idle Would Fluctuate And So Would The Voltage Meter. At First I Thought It Might Be The Spark Plugs, Wires Or Fuel Filter. I Changed Them All And The Problem Was Still There. After Reading The Info Posted Up About Cleaning The Throttle BORE & Blade.... I Decided To Try It... Let Me Tell You The 5.3 Vortec Is Running Smooth With No Idle Fluctuations... Thanks A Bunch ...
Ezramace.

[big pete]

i just bought a 02 tahoe with 28k miles and it seems to have the idle problem that everyone here speaks of. i tried cleaning the throttle body bore from the outside and it didnt help.

[EZRAMACE]

Originally Posted by big pete

i just bought a 02 tahoe with 28k miles and it seems to have the idle problem that everyone here speaks of. i tried cleaning the throttle body bore from the outside and it didnt help.

Im not sure what you mean by cleaning it from the outside, but you need to remove the air duct.....
I'm no mechanic, but I did exactly what this site said to do and it worked! Let me tell you, I had very low idle. At sharp/slow turns, (like in a parking spaces) it would turn off, It was embarrasing at times. So I took that air duct off (held with a large clamp) and sprayed some carb/choke cleaner into the throttle bore (hole about 4" in circumference) and gently rubbed it with a soft toothbrush. That blade was shut so I placed the carb/choke cap under it to hold it open. Then I sprayed some more, cleaned it with the brush again. I even used a soft cloth and rubbed in there, and gently behind the blade. That was all it needed. It seems like a big GIANT problem but you'll be amazed at how easy it was to fix. The throttle was up and it ran or runs like a champ!!!
Good luck!!!

[TexasF355F1]

The engine is suppose to idle at right around 500. Mine does, and so does everyone elses Silvy I know.