[NOT 5.7L] 2001 5.3L low engine idle

[Marky Dissod]

Looking for some help on a low engine idle problem. My 2001 chevy tahoe has a 5.3L engine (NOT a 5.7L, it's not a Mexican Sonora).
My engine idle is around 500-550RpM, and believe it should be around 600-650RpM when idling.
Does anyone know if the computer needs to be reset? or is there a part I need to replace to maintain the 600RpM higher idle?
Don't have any running issues yet, but have issues starting from time to time.

Pcm decides what idle RpM is based on coolant temp, as coolant warms up idle RpM drops.
If I remember correctly, it'll go under 550RpM if coolant is over 212F, which hotter than necessary. GM OE setting to save fuel.
If you want the pcm to actually give a damn about your beliefs you need to get the pcm tuned.

My commanded idle setting never goes under 625RpM (still ain't figured out why my idle can briefly sink to about 225RpM during warmups).
Only time my engine temp ever got over 212F was on a 104F hot summer day stuck in Manhattan stop'n'go.
Both are thanks to getting my pcm tuned, not to mention a considerable list of other improvements.

 

[phil57]

Click on your username in the upper righthand corner of your browser. Click on "Signature" and enter your info in the text box. Click the SAVE button.

View attachment 480015

Thanks, added specs but not sure I have limited slip on diff., Think it would be labeled as G80 but don't se any reference to it in my info.

 

[OR VietVet]

Thanks, added specs but not sure I have limited slip on diff., Think it would be labeled as G80 but don't se any reference to it in my info.

The absolute first time I have seen someone put the RPO code, in their signature, for the A/C and Trailer Package. I love it!!!!

I am a little peeved that you did not include exterior and interior colors though.

 

[phil57]

The absolute first time I have seen someone put the RPO code, in their signature, for the A/C and Trailer Package. I love it!!!!

I am a little peeved that you did not include exterior and interior colors though.

Didn't think that info was that important.
I do have all my existing paper work when ordered new in 2001.
Waiting for cleaner parts to proceed with throttle body and MAF sensor cleaning process. Did watch several videos as you suggested about procedures and ECM/CM relearning process when done. I was wondering if you think the MAF sensor should be replaced due to its 25 yrs old rather than trying to clean it? Due to the wires being so thin on it. Also can I use the MAF sensor cleaner on other ECM elec sensors. Maybe the throttle position sensor and the map sensor?
Not quite sure what the life expectancy of all the sensors throughout the vehicle should be or now long they should last. I don't have any codes currently but due to them being 25 yrs old wondering which ones might be on there last life. Maybe you could let me know what you have experienced, being a certified tech, which common sensors fail and about what K miles to somewhat expect failure.
Thanks again for your help, will let you know what happens after the cleaning, keeping fingers crossed reset learning goes as expected when done.

 

[OR VietVet]

Didn't think that info was that important.
I do have all my existing paper work when ordered new in 2001.
Waiting for cleaner parts to proceed with throttle body and MAF sensor cleaning process. Did watch several videos as you suggested about procedures and ECM/CM relearning process when done. I was wondering if you think the MAF sensor should be replaced due to its 25 yrs old rather than trying to clean it? Due to the wires being so thin on it. Also can I use the MAF sensor cleaner on other ECM elec sensors. Maybe the throttle position sensor and the map sensor?
Not quite sure what the life expectancy of all the sensors throughout the vehicle should be or now long they should last. I don't have any codes currently but due to them being 25 yrs old wondering which ones might be on there last life. Maybe you could let me know what you have experienced, being a certified tech, which common sensors fail and about what K miles to somewhat expect failure.
Thanks again for your help, will let you know what happens after the cleaning, keeping fingers crossed reset learning goes as expected when done.

I was joking about the two RPO codes you posted and the colors. None of them hardly ever come up unless in a specific thread. Unless the MAF cleaner states on the can, that it can be used for other sensors, do not do it. If there is not a cleaner for it, use the sensor till needs to be replaced. Unfortunately, I am a bad example of "waiting till something is bad before replacement". If you look in the Under Construction thread and find mine, you will see that I actually threw money at my 2005 Tahoe Z71 and replaced a plethora of components before they were bad. You would need to be sure that you were/are going to keep your 2001 Tahoe till it dies. I knew I was keeping my Tahoe and a friend has a shop and was willing to allow me to use his lift and also help with the work. You will see where I replaced Sooooo many components that were not bad yet. You have a cable throttle and I have a drive by wire. There would be some differences. I have hydro-boost brakes and you have vacuum boost brakes, I assume.

Clean the MAF. Remove the throttle body and clean both sides. If you are careful with the throttle plate and move it sparingly and slowly, during the cleaning process, I would bet there will be no relearn needed. When you have the money and time and the "want to do it", do the oxygen sensors. If you do the TPS, do the connector at same time. Use Genuine GM every chance you get and then AC Delco if have to.

 

[LsHart]

It's a 30 yo vehicle that only you know the condition of and history of, too many variable factors to even offer a guess. I'd start with an evaluation of systems underhood, a code scan and a fuel pressure test for starters.

Carbon build up in intake. Restricting air flow?

 

[LsHart]

No need to replace what isn't broken. Just cleaning the throttle body inside and out makes a big difference. Try this, suck air through a straw for months on end and eventually trash will build up in the straw and make it harder to pull air. Thus, pcm determines to pull fuel back for the lack of air. Clean mass air flow with mass air flow sensor cleaner, clean throttle body. If carbon build up in cylinders, change plugs and fuel filter if u have one . If it's never been tuned. U will not need one. Use a scanner and reset fuel trims. Take 2 of these and call us in the morning!

 

[phil57]

I was joking about the two RPO codes you posted and the colors. None of them hardly ever come up unless in a specific thread. Unless the MAF cleaner states on the can, that it can be used for other sensors, do not do it. If there is not a cleaner for it, use the sensor till needs to be replaced. Unfortunately, I am a bad example of "waiting till something is bad before replacement". If you look in the Under Construction thread and find mine, you will see that I actually threw money at my 2005 Tahoe Z71 and replaced a plethora of components before they were bad. You would need to be sure that you were/are going to keep your 2001 Tahoe till it dies. I knew I was keeping my Tahoe and a friend has a shop and was willing to allow me to use his lift and also help with the work. You will see where I replaced Sooooo many components that were not bad yet. You have a cable throttle and I have a drive by wire. There would be some differences. I have hydro-boost brakes and you have vacuum boost brakes, I assume.

Clean the MAF. Remove the throttle body and clean both sides. If you are careful with the throttle plate and move it sparingly and slowly, during the cleaning process, I would bet there will be no relearn needed. When you have the money and time and the "want to do it", do the oxygen sensors. If you do the TPS, do the connector at same time. Use Genuine GM every chance you get and then AC Delco if have to.

I do plan on keeping it until it dies. Kind of got attached to the Tahoe, now its a quest to see how long it will last.
I do have throttle cable with separate cruse cable connection. Issue I have with disconnection of plastic parts (cruse cable connection) they seem very brittle due to age and heat, so try to be careful not to crack them, starting to try some armor-all on outside of plastic connections to try to revive the plastic a little.
Curious about why you recommend changing the TPS connector?
Also wondering why you recommend Gen. GM or AC Delco vs other OEM parts? Is there something specific about the GM & Delco parts vs the OEM parts by others? Wondering what your thoughts or experience is about the diff..
Will do the O2 sensors this summer.
Do you recommend changing the frt 4WD CV jts/axles? Had to change axle u-jts this yr due to heard squealing noise on rear main axle shaft. One u-jt was frozen. So did both frt & rear axle u-jts. Don't feel any frt vibration yet but figure if other jts were worn the frt CV jts might not be far behind on wear. Changed frt wheel knuckles a couple of yrs ago due to bearings wore out.
Thanks for all the info, will check your "Under Construction thread" when I have time, thanks.

 

[OR VietVet]

I do plan on keeping it until it dies. Kind of got attached to the Tahoe, now its a quest to see how long it will last.
I do have throttle cable with separate cruse cable connection. Issue I have with disconnection of plastic parts (cruse cable connection) they seem very brittle due to age and heat, so try to be careful not to crack them, starting to try some armor-all on outside of plastic connections to try to revive the plastic a little.
Curious about why you recommend changing the TPS connector?
Also wondering why you recommend Gen. GM or AC Delco vs other OEM parts? Is there something specific about the GM & Delco parts vs the OEM parts by others? Wondering what your thoughts or experience is about the diff..
Will do the O2 sensors this summer.
Do you recommend changing the frt 4WD CV jts/axles? Had to change axle u-jts this yr due to heard squealing noise on rear main axle shaft. One u-jt was frozen. So did both frt & rear axle u-jts. Don't feel any frt vibration yet but figure if other jts were worn the frt CV jts might not be far behind on wear. Changed frt wheel knuckles a couple of yrs ago due to bearings wore out.
Thanks for all the info, will check your "Under Construction thread" when I have time, thanks.

Genuine GM is the OEM parts. AC Delco is a step down but still quality and is a substitute for the Genuine GM. You can even go to a dealer and they will hand you AC Delco parts bags/boxes/containers. AC Delco is same in a lot of cases. There are no other OEM parts suppliers. Also, GM does not make all their parts they sell. A lot of the GM or ACD parts are made by other manufacturers and just stamped and boxed with GM on them. I have preferences for other substitute parts: Delphi and NGK are good for me.
GM does recommend replacing the TPS connector, when you do the TPS. I don't argue with the GENERAL.
When you do the O2's, do them all at once. Do not mix and do not do 1 or 2 at a time.
You said you changed axle u-jts and I think you meant driveshafts u-joints. I would have done them all, too. Timken is a good hub bearing assbly if Gen GM and AC Delco are not available.
You don't need to do the front cv axles as long as they are not making noise and the boots are intact. When you see my Build Thread, you will see that I did those axles, just because.

 

[strutaeng]

I paid a little attention the to the tachometer on my 99 Silverado yesterday...looks like in P.

Have you hooked up a scanner that has live data? That will show what the actual rpm is. I don't think the cluster has super high resolution TBH. Maybe the needle on the tach was removed to replace a burnt bulb and reinstalled a tiny bit off? You are not the original owner, right?

I'm still not convinced you have a problem? You'd may have a CEL light on if you had a problem with idle RPM?

I believe on these engines you could alter the idle RPM via that screw on the throttle body? I can't remember now. Or increase the RPM on the tune.

 

[Fless]

AC Delco offers several tiers of parts, so buyer beware:

AC Delco Parts Tiers

 

[Marky Dissod]

Genuine GM is the OEM parts. ACDelco is a step down, but still quality, and is a substitute for the Genuine GM.

If your vehicle is over 10+ years old, there is no longer such a thing as 'genuine GM' OE parts, even if 'genuine GM' or 'ACDelco' are still better bets.

 

[OR VietVet]

If your vehicle is over 10+ years old, there is no longer such a thing as 'genuine GM' OE parts, even if 'genuine GM' or 'ACDelco' are still better bets.

I have had member @915_Tahoe, look and find Genuine GM NOS parts. May not be listed but can be out there. Can even find on ebay.

 

[houstontaylor]

On my 2003 Tahoe I had problems with low and slightly rough idle. My experience is that it can be from the fuel system or a vacuum leak. It might help to have a scan tool with live data to check on that and there are videos online to tell how to interpret fuel trims. One thing is the starting difficulty. That sounds like the fuel system is losing pressure when the engine is shut off, hence your running the fuel pump before cranking helps to pressure it back up. It can be losing fuel pressure past the fuel pump check valve, a fuel injector, or the fuel pressure regulator. As part of my investigation I also found that the original MAP sensor rubber seal was worn out and leaking vacuum. Also, I found that I had vacuum leaks around some of the fuel injectors since I had replaced them but didn't lubricate the o-rings before inserting and damage occurred. Found that out with a smoke test with the intake duct blocked just past the MAF sensor. The check valve on my new fuel pump was leaking and so the system lost pressure when the engine was shut off. Had to replace it again. Additionally, I also had problems with the fuel guage from a bad electrical connector on the old style fuel pump (2x2 square connectors on two different pumps that were bad - use the new flat 1x4 connector redesigned pump type if you replace the pump, although it appears you have lots of pressure). It sounds like your vehicle has lots to teach you like mine did (does). Haha.

 

[Marky Dissod]

If your vehicle is over 10+ years old, there is no longer such a thing as 'genuine GM' OE parts, even if 'genuine GM' or 'ACDelco' are still better bets.

I have had member @915_Tahoe, look and find Genuine GM NOS parts. May not be listed but can be out there. Can even find on ebay.

To clarify:
Even GM will not typically provide quite the same GM OE standard after 10+ years.
It's great that NOS can be found now and again, but when GM sources run out of those ...

 

[phil57]

Genuine GM is the OEM parts. AC Delco is a step down but still quality and is a substitute for the Genuine GM. You can even go to a dealer and they will hand you AC Delco parts bags/boxes/containers. AC Delco is same in a lot of cases. There are no other OEM parts suppliers. Also, GM does not make all their parts they sell. A lot of the GM or ACD parts are made by other manufacturers and just stamped and boxed with GM on them. I have preferences for other substitute parts: Delphi and NGK are good for me.
GM does recommend replacing the TPS connector, when you do the TPS. I don't argue with the GENERAL.
When you do the O2's, do them all at once. Do not mix and do not do 1 or 2 at a time.
You said you changed axle u-jts and I think you meant driveshafts u-joints. I would have done them all, too. Timken is a good hub bearing assbly if Gen GM and AC Delco are not available.
You don't need to do the front cv axles as long as they are not making noise and the boots are intact. When you see my Build Thread, you will see that I did those axles, just because.

Finished cleaning off throttle body and MAF sensor yesterday and idle is still at 550 RPM's. I believe it should be around 600 or 650 RPM's. Haven't run it with A/C on yet to see if it idles up for the added load due to giving it some time for everything to calibrate again (a couple of trips with 1/2 hr run time) and see if any codes show up. There is an adjustment screw on the bottom of the pedal/cruse cables connection point at the throttle body assembly. Should the screw be adjusted to idle at 625 rpm's after some calibration time?

 

[Fless]

I may have missed it, but how does the idle value compare when using a scan tool to read it?

 

[Marky Dissod]

Finished cleaning off throttle body and MAF sensor yesterday and idle is still at 550RpM. I believe it should be around 600 to 650RpM.
Haven't run it with A/C on yet to see if it idles up for the added load due to giving it some time for everything to calibrate again (a couple of trips with 1/2 hr run time)
and see if any codes show up.
There is an adjustment screw on the bottom of the pedal/cruse cables connection point at the throttle body assembly.
Should the screw be adjusted to idle at 625RpM after some calibration time?

If adjusting the idle set screw does NOT achieve the desired affect, you'll have to resort to having your pcm tuned.
Prior to having my pcm tuned it idled @ about 500-550RpM, depending on coolant temp.
It idled a bit higher at startup, of course, but as it warmed up the idle went down gradually.

Once I had my pcm tuned - on top of several other benefits, some immediately obvious, some apparent over time, some occasionally appreciated -
my warm'd up idle never goes under 625RpM.

 

[phil57]

I may have missed it, but how does the idle value compare when using a scan tool to read it?

Engine RPMs read 550 on scan tool with engine temp 195 after warm up. Engine idles higher at cold start (seems normal for cold start) and comes down to the 550. Starting issues seem to have gone away, seems like no more none starts when key turned so far. I have no engine codes on scanner either. The intake side of the throttle assembly had a black carbon film on it. Some on the throttle flapper edges and hole (on engine side) but not any on the intake side between throttle body and MAF sensor. Looked like the intake chamber on engine has a slight carbon residue build up on it also. Is there any additive I can use to try to clean or eliminate it?

 

[phil57]

I paid a little attention the to the tachometer on my 99 Silverado yesterday...looks like in P.

Have you hooked up a scanner that has live data? That will show what the actual rpm is. I don't think the cluster has super high resolution TBH. Maybe the needle on the tach was removed to replace a burnt bulb and reinstalled a tiny bit off? You are not the original owner, right?

I'm still not convinced you have a problem? You'd may have a CEL light on if you had a problem with idle RPM?

I believe on these engines you could alter the idle RPM via that screw on the throttle body? I can't remember now. Or increase the RPM on the tune.
View attachment 480201

Thanks for the input. Did use scan tool with live data and RPM's at 550 w/temp at 195. I'm thinking I'll try the adjusting screw to see if I can hold the 625 RPM's with running temp and no cold start issues down the road. Otherwise I'll see if the PCM can be programed to hold the 625 idle in the future. Thinking after 25 yrs of having the throttle resting plate hit the adjusting screw could have warn to the lower idle position vs the PCM being off. Seems the no start issues went away once I cleaned the throttle body and MAF sensor. So could be the low idle is a non issue. Only time will tell now. Don't have any stalling issues or rough idling issues and no codes on scannner.