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Can a stuck tranny valve cause my throttle sticking???

This is a discussion on Can a stuck tranny valve cause my throttle sticking??? within the General Help forums, part of the LSx Technical Help Section category; In depth q here. Have a 2012 tahoe 4wd 6L80 that was experiencing harsh shifts and even that lunging forward ...

  1. #1
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    '12 Tahoe 5.3L 6L80 4wd

    Tranny issue cause my throttle sticking? Replaced everything

    In depth q here. Have a 2012 tahoe 4wd 6L80 that was experiencing harsh shifts and even that lunging forward sensation when going slow where it felt like my car was being hit from behind. I drive for uber so this wasn't acceptable. To fix the transmission shifts, I went ahead and added half a bottle of seafoam trans tune (which boasts that it isn't a leak stopper, just will free up valves?), and within 5 min of adding it, shifting got much better. Unfortunately, about 20 min later, the throttle began sticking horribly. Its most noticeable in low gears like first and second, and when you take ur foot off the accelerator, it stays at the same rpm and continues to move forward with the same velocity for about 3 seconds(Also i will add if you get going a good speed and shift the car into neutral and let it coast to a stop, the throttle jumps from 550 to 1000 every few seconds until the car comes to a stop. Also if you rev it in park or neutral, it takes longer than normal for the idle to return to 550). As per the instructions of seafoam, I changed the atm fluid within a 100 miles of adding it, so I had the fluid completely flushed and even dropped the pan and changed the filter. It didn't do anything to mitigate the throttle sticking. The harsh shifts have subsided, but they have been replaced by this throttle sticking, which is just as dangerous. To rule EVERYTHING out, I changed the throttle body (which was BLACK-i'm guessing previous owner had an over oiled K&N), so I changed the entire throttle body(throttle by wire, inlcudes TPS sensor), changed the MAF sensor and even changed the accelerator pedal. Nothing has an affect. So logic would indicate that something changed when I added the seafoam and possibly something was stuck in 1 transmission valve to cause the harsh shifts, moved through the valve body and is now sticking in another valve that's causing the throttle to stick. Is this even physically possible? Can a clogged or leaking transmission valve cause the throttle to want to maintain its current RPM? I've never gotten any engine codes related to this situation, just a o2 sensor a while back that the dealer fixed. Has anyone ever heard of this and have any ideas for a remedy? Is the only thing I can do is have the tranny dropped and valve body opened? Does anyone familiar with the 6L80e have any intuition what valve I should start by looking at or ever heard of this happening?? Thanks for the help. I'm not very mechanically inclined, only can do basic stuff, and certainly cant drop a tranny or work on the valve body myself. Would def have to pay someone do it.
    Last edited by TahoeTruk; 02-10-2016 at 07:51 PM.

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    sounds like quite possibly a vacuum leak or something along those lines. Easy enough to check. Spray a little carb cleaner around the vacuum lines while the truck is idling and see if the idle goes up paying close attention to the pcv hose. Any codes being thrown at all? To answer you're question...no...I don't think the tranny is to blame here. Short of a converter staying locked I don't see how it could cause your issues and a locked converter would have different symptoms. It really sounds to me like the truck is getting some unmetered air because that'll effect your idle, running airflow, and shift patterns.
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    '12 Tahoe 5.3L 6L80 4wd

    Yeah I agree it does sound like the symptoms vacuum leak however I really don't hear any hissing sound but I'm still going to investigate that. I'm going to buy a vacuum gauge and hook it up to the brake booster hose. Is that what you recommended and seeing if it holds the proper pressure? What sort of play in the pressure would be indicative of a leak. Never done this before. No engine codes

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    I've always just sprayed a little carb cleaner around the vacuum lines. I know on the fbody the pcv line likes to crack in the back of the bend where it turns to go into the intake. You won't necessarily hear it hissing.

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    to address another issue in your post.....the oil in your throttle body is probably from the pcv system. You can add a catch can to the pcv system to correct that.

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    Would also guess a vacuum leak.
    It's on jackstands.

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    '12 Tahoe 5.3L 6L80 4wd

    So I listened real close today and I actually heard a slight hissing sound coming from behind the intake manifold against the firewall. Maybe one of the hoses back there. I sprayed a bunch of carb cleaner around that area but obviously couldn't get behind the manifold and couldn't elicit a change in idle. I bought a vacuum gauge and will try tomorrow and see what the reading is. @orion Also, regarding the PCV valve. On the V8 it's a PCV "orifice" and apparently there's two hoses. One coming from air intake going to r valve cover. And then anothe coming out of left valve cover and wrapping behind intake manifold against the fire wall I guess? I'm not sure? I can't figure out which nose it is coming out of left valve cover.
    Last edited by TahoeTruk; 02-11-2016 at 10:37 AM.

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    '12 Tahoe 5.3L 6L80 4wd

    So I listened real close today and I actually heard a slight hissing sound coming from behind the intake manifold against the firewall. Maybe one of the hoses back there. I sprayed a bunch of carb cleaner around that area but obviously couldn't get behind the manifold and couldn't elicit a change in idle. I bought a vacuum gauge and will try tomorrow and see what the reading is. @Orion Also, regarding the PCV valve. On the V8 it's a PCV "orifice" and apparently there's two hoses. One coming from air intake going to r valve cover. And then anothe coming out of left valve cover and wrapping behind intake manifold against the fire wall I guess? I'm not sure? I can't figure out which nose it is coming out of left valve cover.

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    '12 Tahoe 5.3L 6L80 4wd

    So I listened real close today and I actually heard a slight hissing sound coming from behind the intake manifold against the firewall. Maybe one of the hoses back there. I sprayed a bunch of carb cleaner around that area but obviously couldn't get behind the manifold and couldn't elicit a change in idle. I bought a vacuum gauge and will try tomorrow and see what the reading is. @ Orion Also, regarding the PCV valve. On the V8 it's a PCV "orifice" and apparently there's two hoses. One coming from air intake going to r valve cover. And then anothe coming out of left valve cover and wrapping behind intake manifold against the fire wall I guess? I'm not sure? I can't figure out which nose it is coming out of left valve cover.

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    check your a/c vents inside the car and see if they're working properly. There's a small vacuum line that branches off behind the intake that controls the vent operation. Common for those to break also. Yeah...that pcv system pulls from the valve covers via the intake. The valve sits on top of the passenger side valve cover. There's a metal grounding bracket attached to the passenger fuel rail.

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    '12 Tahoe 5.3L 6L80 4wd

    @Orion, I noticed the passenger side air vents are slightly weaker than the driver side vents. Do you think this could relate to anything with the AC vacuum or do you think you if there was a prob it would apply to all four vents?

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    it wouldn't switch from like defrost to the vents or vents to floor....wouldn't really effect balance between vents. If vents are that noticeable it could either be something in the vents or a mouse has chewed a hole in one of the vents or something.

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    '12 Tahoe 5.3L 6L80 4wd

    I got to tell you, I really still think this is a tranny issue. I drive this car for eight hours every day Bc I drive for uber, and I really have time to sit there and analyze what's going on and it really feels like a valve is sticking with in the transmission and then when it surges sometimes it's like popping the clutch and then when it holds the gear it's almost like it's not computing the proper load that has eased off as I'm decelerating and it's pushing the car harder not disengaging the clutch

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    at the end of the day you're the one in the truck so you have the better idea of what it feels and acts like.....have to remember I'm in front of a computer screen making a "best guess" based on what I'm reading. Go with your gut or take it in somewhere and have someone check it out for you. Update the thread though if you would when you get it figured out as I would like to know.

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