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Occasional stalling at idle...

BretD04GMC

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BretD04GMC Enthusiast

BretD04GMC

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I'm curious if anyone else is/or has experienced this with their GMT-800 series.

I have a 2004 Sierra with the 5.3L. It typically runs very reliably, but on occasions since I've owned it, it will develop a stumble when coming to a stop. This in turn triggers the low oil pressure warning and the truck shuts down and the alarm bell starts going off.

A quick throw into neutral and turning the key, and it will refire and I'm on my way. Still, it's really unnerving, especially in stop-and-go traffic.

This morning it acted up again, and stalled 4 or 5 times on me. I finally ended up just letting the truck roll over to the side of the road to get out of traffic. At that point, I turned the key completely off and removed it from the ignition. Then I let the truck sit for a couple minutes, before I restarted and merged back into traffic. After that, it was fine all the way to work.

 

My thinking is that it's a glitch with the drive-by-wire system, and by completely shutting down the truck the throttle body controller resets itself.

There's no TSB's that I can find related to this, so I'm wondering how common this is?

txab Senior Enthusiast

txab

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Have you cleaned the throttle body?

 

How many miles and what maintenance has been performed?

BretD04GMC Enthusiast

BretD04GMC

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The truck currently has 101,000 miles on it. However, it's done this random stalling since I bought it back in 2005 when it only had 6,500 miles on it.

Last year, while it was at the dealer for some other service, I had them do a throttle body cleaning since it had never been done. Right after getting it back from the dealer, it acted up and stalled on me. I then did a second cleaning on the throttle body myself.

It will go for weeks with no trouble, then all of a sudden one day it will act up. Then the problem goes away and the truck runs fine for weeks again.


In past Google searches, I've come across a random post or two on other forums where people have had a similar issue (truck stumbling/stalling when slowing down or turning a corner – triggering the low oil pressure alarm), but with no real answer or solution.

BretD04GMC Enthusiast

BretD04GMC

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No stored codes. I have a Scan Gauge II mounted above the rear view mirror to monitor coolant temp, trans temp, voltage and mph. It also has the ability to check for codes and clear the ECM.

The truck was just into the dealership for an unrelated problem (hybrid battery system code), and they reported no other codes. I also had them do a radiator flush, since it was due.

As a first step, I'll probably clean the throttle body this weekend and look it over.

 

 

Also, after doing some searching I came across a post on another forum where a GM Tech gave someone this answer:
"I have been fixing these trucks with this idle stumble and a/c inop. since the electronic throttle body came out on the trucks. The throttle body actuator is binding up and causing the unstable idle. I have tried cleaning them and so on with no luck. Replace the throttle body and gasket and take it to the dealer and have them update the pcm to also improve the idle stability."

bossier62guy Senior Enthusiast

bossier62guy

Posted
Posted

Having worked on military aircraft for over 20 years I can tell you that intermittent problems are a pain in the a$$.....It would be better if it just shut down and stayed down. If you do get it fixed please come back and let us know what corrected it. Good luck...

One question though....after 7-8 years why are you so interested in fixing it now? LOL

txab Senior Enthusiast

txab

Posted
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You left out a ton of pertinent information in your op. You have the hybrid engine option on your vehicle which is quite bit different than the others. Your engine shuts off when stopped, then restarts when you want to move again. Does it have this problem when you disable the the auto-stop by running in tow haul? Have you had the dealer look into this?

 

Ever had the fuel pump replaced or tested, since the gmt 800 had a rash of bad pumps

 

I'd still remove the TB and clean it and check it. It's going to be dirty, if it has never been cleaned Might not clear your problem. I had a friend that had the same model and engine/hybrid. He had so much trouble with over the years as soon as warranty was gone he got rid of it

BretD04GMC Enthusiast

BretD04GMC

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You left out a ton of pertinent information in your op. You have the hybrid engine option on your vehicle which is quite bit different than the others. Your engine shuts off when stopped, then restarts when you want to move again. Does it have this problem when you disable the the auto-stop by running in tow haul? Have you had the dealer look into this?

 

Ever had the fuel pump replaced or tested, since the gmt 800 had a rash of bad pumps

 

I'd still remove the TB and clean it and check it. It's going to be dirty, if it has never been cleaned Might not clear your problem. I had a friend that had the same model and engine/hybrid. He had so much trouble with over the years as soon as warranty was gone he got rid of it

 

1) YES – the truck will do this even in tow-haul mode or with the windshield defroster on. Both modes disable the autostart/stop function of the hybrid system.

 

2) NO – I never had the dealer look into it. My thinking being that it happens so randomly, that most likely they won't be able to recreate the condition. Which means they'll say bring it back if it gets worse or if you get a hard failure.

 

3) NO – never had any issues with the fuel pump.

 

4) The throttle body has been cleaned by the dealer in the past – about a year ago. It stalled within days of getting it back from them. I checked it over for any loose clamps on the air intake and also cleaned the throttle body again while it was on the truck. The problem cleared up and it ran fine for a while.

 

Overall, my truck has been pretty reliable. This is the only nuisance item. Other people have reported the same problem with their non-hybrid GM trucks. Most responses on other sites range from "try cleaning the TB" to "the fuel pump might be bad" with no real answer as to the source of the problem. Mainly just people throwing parts and money at the problem hoping for a fix.

 

I'm leaning toward thinking it's a bug in the actuator on the throttle body. Just like the junk instrument clusters GM put in the 800 series with the low quality stepper motors that go bad.

txab Senior Enthusiast

txab

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One thing I'd check is the wiring at the TB. Check the wiring where it goes into the back of the plug. I know a friend that was having a similar problem and we discovered one of the wires had pulled out of the back of the plug slightly, making intermittent contact. Once this was repaired, no more complaints.

 

Reason I wondered if your problem occurred when locked out, I know at one time several of those vehicles needed to have the ECM re-flashed with updated programming

waumo1 Enthusiast

waumo1

Posted
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This is probably irrelevant information for you but it is free. The only vehicle I ever had that stalled sometimes when decelerating to a stop was a 94 Buick with the 5.7L LT1 engine. It was the EGR valve. What finally clued me to it was the fact that sometimes from a stop under very light acceleration it would stumble a little. This got me to thinking lean condition then to EGR which was the problem. I disassembled the EGR and it was carboned up. I had to do that about every 20K on the car.

BretD04GMC Enthusiast

BretD04GMC

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One thing I'd check is the wiring at the TB. Check the wiring where it goes into the back of the plug. I know a friend that was having a similar problem and we discovered one of the wires had pulled out of the back of the plug slightly, making intermittent contact. Once this was repaired, no more complaints.

 

Reason I wondered if your problem occurred when locked out, I know at one time several of those vehicles needed to have the ECM re-flashed with updated programming

That's a good suggestion on the wiring. I'll check the connection.

 

I remember reading not long after I bought the truck that GM had issued a software update. I'd have to check my records to see if that was ever done. I do know there is a TSB to change the oil pressure alarm reaction time on the hybrid autostart function from 2 seconds to 12 seconds. The reason being that on a hybrid restart, there's no RPM flare and the oil pressure takes a hair longer to build up. This can potentially trigger the low oil psi alarm.

 

My problem is definitely due to the idle stumbling when slowing down. When it happens, the RPM will dip below 500 and cause the oil psi to drop low enough to trigger the fail-safe.

txab Senior Enthusiast

txab

Posted
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Might look at this youtube video. He's getting "Reduced Engine Power" code. It'll give you an idea of what you're looking for

 

 

 

BretD04GMC Enthusiast

BretD04GMC

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Might look at this youtube video. He's getting "Reduced Engine Power" code. It'll give you an idea of what you're looking for

The link didn't show up in your reply.

BretD04GMC Enthusiast

BretD04GMC

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Current update:

The truck ran fine today to and from work. However, while running some errands on the way home the truck stalled while pulling into a shopping center driveway. This time the "Battery Not Charging" message appeared on the DIC.

Putting it in neutral right away and trying to start the truck didn't work. It wouldn't turn over. I then put it in Park, turned off the ignition and tried again. The truck fired up and I was rolling. Then, while rolling into a parking space it stalled again and the Low Oil Pressure Alarm went off. I did my errand and it drove home fine from there.

So, tonight I do a search for the "Battery Not Charging" message and I found this:
http://www.gm-trucks.com/forums/topic/150665-aftermarket-devices-plugged-into-data-link-connector/?hl=%2Bbattery+%2Bnot+%2Bcharging

I'm now wondering if it isn't my Scan Gauge II that's the culprit of my intermittent stalling issue.

txab Senior Enthusiast

txab

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Have you had it place prior to your stalling problems? Disconnect and drive. Hopefully this is your problem and it will be solved

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