Issues with vehicle stalling intermittantly while slowing or stoping.

Tiny
REDREDKROVY
  • MEMBER
  • 2008 CHEVROLET IMPALA
  • 3.5L
  • V6
  • 2WD
  • AUTOMATIC
  • 201,000 MILES
My daughter has a 2008 Chevy Impala LS with the 3.5 flex engine. When she comes to a stop at a red light or stop sign it will stall and quit. This is an intermittent issue that seems to happen once the engine warms up. Starts happening after driving the car for around 2-3 miles. There doesn't seem to be any issues accelerating or when giving the vehicle gas. Only when stopping or slowing down.

Sometimes we can restart it with little to no issues and sometimes it takes 20-30 minutes to get it to start again. It is cranking and the voltage reads ~ 14 volts when running so I don't believe it's the battery or alternator causing the issue.

I put a fuel pressure gauge on it and I'm getting around 58 psi with the key on but engine off and it stays around 57-60 psi with the engine running. Never drops below 57 psi even when it dies so I don't believe it's the fuel pump.

I've gone out and bought an xTool D7W to try and pin down what's going on. I did get a "System Too Rich Bank 1" DTC while the car was sitting in the driveway idling.

I have replaced the air filter. I recorded some data while the car was sitting in the driveway with the xTool. Thought that the HO2S 1 wildly swinging between like 25mV to 800mV was an issue but after doing some more research that is normal.

I was going to drive it and record at the same time until it dies again. XTool allow me to pick up to 8 fields to record. Which should focus on? What else can I test or do to try and figure this out?
Saturday, June 28th, 2025 AT 7:18 AM

7 Replies

Tiny
REDREDKROVY
  • MEMBER
  • 6 POSTS
Started it, backed out of the driveway, put in drive, started up the road which has a moderate incline, floored it, let off the gas about 150 yards to 200 yards away, once RPMs dropped it shut off within a second or two. Pictures below has a red line at the spot where I let off the gas pedal.
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Saturday, June 28th, 2025 AT 10:16 AM
Tiny
REDREDKROVY
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  • 6 POSTS
Next picture is with the red line where it stalled and shut off.
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Saturday, June 28th, 2025 AT 10:17 AM
Tiny
REDREDKROVY
  • MEMBER
  • 6 POSTS
This is the HO2S sensors and short and long fuel trim at the point where I let off the gas pedal.
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Saturday, June 28th, 2025 AT 10:20 AM
Tiny
REDREDKROVY
  • MEMBER
  • 6 POSTS
This is the HO2S sensors and short and long fuel trim at the point where it stalled and shut off.
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Saturday, June 28th, 2025 AT 10:21 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 52,266 POSTS
Okay, thanks for the graphs, it looks like you may have a vacuum leak or a dirty throttle body. Let's use this video to test for leaks.

https://www.youtube.com/watch?v=LRKWV4Are5c&t

Next please go over this guide to help service the throttle bore with instructions below to help you as well.

https://www.2carpros.com/articles/throttle-actuator-service

Please read the guide before you begin. Check out the images (below). Let us know how it goes.
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Saturday, June 28th, 2025 AT 1:16 PM
Tiny
REDREDKROVY
  • MEMBER
  • 6 POSTS
Update time and I'm pretty sure the engine locked up. After the last event I couldn't get the engine to crank. I thought it was a bad battery so I went ahead and purchased a new one. Tried again this morning. I could hear the starter solenoid click but the engine didn't crank at all. I put the new battery on a charger and tried again about 10-20 minutes later. The engine cranked very slowly once or twice and then just stopped. Put the battery back on the charger for a bit. Tried again, solenoid clicked but the engine didn't crank. Thought maybe I need more juice so I pulled my Audi Q7 which is diesel up beside it and put jumper cables on it. Let it charge for like 30 minutes. Tried again, I can hear the solenoid but the engine doesn't crank.

It seems kind of odd that the starter would go out at the same exact time this is happening so I decided to pull the serpentine belt off and try to start it, in case I had a pulley or something locked up. I can turn the pulley's, alternator, and water pump by hand with no issue. Still, just a click with no crank.

So I decided to try and turn the crank by hand. Below is a video of me doing that. I have the vehicle in neutral. I can't get it to budge and I'm scared to put too much force behind it and snap the bolt off.

What do you think? Do I need to put more force behind it? Did I break a rod or something? I would have expected some very loud noises when it stalled and died if I had. I'm not for sure at this point.

When trying to start the engine today with the new battery and even after charging it, looking at the scanner the voltage was dropping to 6 volts. Makes me think the starter is getting juice but it's in a bind physically which if the engine is locked up would make sense but maybe I'm wrong.

Do I need to pull the starter off and get it tested or should I just tow this thing to a cliff and push it off?
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Monday, June 30th, 2025 AT 10:45 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 52,266 POSTS
Yep, that does not look good, I would check the engine oil, then remove the drive belt and spark plugs and try to rotate the engine again. Thanks for the video, it helps. Let me know what you find.
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Monday, June 30th, 2025 AT 11:27 AM

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