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I've been having a problem with my 2009 5.3L Suburban. Under…

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I've been having a problem...
I've been having a problem with my 2009 5.3L Suburban. Under long and heavy braking, I will experience a drop in the RPMs, and the RPMs will bob up and down for a brief period. In worst cases, the RPM's drop so low that power goes out, power steering is lost, and a stall can occur while in the middle of driving. It's happened (car stalls while driving) about a half dozen times over the last several months.The common factors when the car loses power steering and stalls are these:
1) Car is under high power load (AC on full blast, stereo on)
2) While turning
3) While breaking for an extended period of time (3+ seconds)
4) Travelling at speeds of 30 - 50 mphWhat has been changed in the last 3 months:
- New alternator
- New fuel pump
- New throttle body
- New brake booster, master cylinder, brake check valve and grommetThe fuel pump was changed about two months ago and that seemed to help avoid the occurrences of stalling. The car has only stalled once after the fuel pump change. But the general issue of the RPMs dropping and bobbing under heavy braking has not gone away despite changes of all the above items.The dealer came to the conclusion that the brake booster / master cylinder was to blame, and there was a vacuum leak from those parts, but even after changing them, I still witness the rpm drop and fluctuate under heavy breaking and heavy power load.I think I have a vacuum leak, still, but I assumed that replacing the brake parts (booster / master cylinder / brake check valve) would have resolved things. If I have a vacuum leak at say, the intake manifold, would this cause the RPM drop situation I'm experiencing while braking? Separate, but possibly related, is that I have had a light whistling sound when the car is running (vacuum leak?), which can be heard lightly while parked in idle, and most clearly when having the foot on the gas at about 40 - 60mph. The whistle sounds like what I recall the noise of a diesel turbo charged truck sounding like.The brake booster vacuum hose was not changed during the brake booster and master cylinder fix. But when I feel around on the hose, including in the far back behind the engine, I don't feel any obvious slices or rips in the hose that might be the source of the vacuum.I'm a bit stumped but thinking this is still a vacuum leak issue? Thanks!
Submitted: 8 months ago.Category: Chevy
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Answered in 15 hours by:
11/18/2017
Chevy Mechanic: Eric, Automotive Repair Shop Manager replied 8 months ago
Eric
Eric, Automotive Repair Shop Manager
Category: Chevy
Satisfied Customers: 34,939
Experience: 20+ yrs. experience as repair shop manager and technician.
Verified

HI,

I am sorry that you have not been helped yet. I just came online and saw your question

Ok, I need to get the last 8 of the vin number to pull the vacuum diagrams as I agree that this is most likely a vacuum issue.

I also need to know if the check engine light is on

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Customer reply replied 8 months ago
Hi Eric, thanks. Never had a check engine light. Here's the full VIN: 1GNFC16JX9R199162Also, one additional note:. When the car has stalled while driving, it quickly starts up again by putting the vehicle in neutral while moving and re-starting. There's no issue in restarting it.
Chevy Mechanic: Mike, Auto Mechanic replied 8 months ago
Mike
Mike, Auto Mechanic
Category: Chevy
Satisfied Customers: 497
Experience: Lead Tech at Solis Auto Repair
Verified

Hello, my name is***** will be helping you out! I have over thirteen year of experience in the automotive industry for numerous different makes & models. I enjoy doing what I do, it is my life.

Do you have a scan tool to read live data stream?

Were any components you listed replaced PRIOR to the issue occuring?

Are you able to pin point the vacuum sound?

Any other conditions or details you can explain, such as more problems after fueling.

I would like to review the fuel trim long term and short term data.

Have you tried applying butane or another fuel source around suspected vacuum areas, or have you had a smoke machine available?

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