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Off throttle RPM

Discussion in 'Performance' started by 1999BlueTahoe, Nov 9, 2020.

Sponsored By: Black Bear Performance
  1. 1999BlueTahoe

    1999BlueTahoe TYF Newbie

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    Good morning y’all. I have been experiencing something kind of weird with my newly purchased ‘99 Tahoe 350 4WD. Let me start by stating I am not very familiar with automatics and have mostly owned/DD’d manual transmissions.

    The thing I’m noticing is that when I’m driving around and let off the throttle the RPMs drop to about 1-1.4K and feels like truck is still lightly throttling. Usually after some braking the RPMs will drop to the sub 1000’s. Kind of curious what might be causing this? I’m not hugely bothered by it other than it forces me to brake harder in certain situations. My friend mentioned that someone might have advanced the timing a bit. He mentioned that based on that RPM weirdness and the fact that the truck kind of starts like a race car. When you start it, it almost feels like either the battery or starter are getting tired. Kind of sounds like it struggles to to start for a couple seconds and then fires right up. I have no idea either way and would love some thoughts on the subject. Thank you.
     
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  2. 1999BlueTahoe

    1999BlueTahoe TYF Newbie

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    Also forgot to mention that one of the previous owners deleted the cats. Not sure if that could contribute or not.
     
  3. drakon543

    drakon543 Full Access Member

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    starter issue is common problem if it still has the old school style starter. unless the truck is tuned the timing cant be advanced in the normal fashion. the ecm monitors the timing from 0 and it has to stay within + or - 2 degrees i think the number was or it will stay throwing p1345. sounds more like your idle air control valve is hanging up a bit. back to the starter, alot of the 90s trucks and suvs came with the standard old school starter. some came with a pgmr starter which uses less power but supplies more torque due to its gearing. they are generally interchangeable.
     
  4. 1999BlueTahoe

    1999BlueTahoe TYF Newbie

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    Thank you for the reply. I have no idea if it’s the original starter or not, probably is though. The truck only has about 138k miles. Definitely good to know about timing with these vehicles and no idea if it’s been tuned or not, I doubt it though. Only “mods” it has is the cat deletes as far as I can tell and the only codes are related to the two missing cats and a dead wheel speed sensor. I will definitely look into both the starter and IACV. Anything else that might be worth checking out?
     
  5. drakon543

    drakon543 Full Access Member

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    possible vacuum leaks but if it was related to that id expect it to be more of an issue. also using proper maf cleaner cleaning the maf might be something worth doing. the tps is also a known culprit for causing wierd problems. sometimes it wont even trip a cel until it causes a different problem. i ended up doing the tps and the harness plug on my 97.
     
  6. Big Mama

    Big Mama Full Access Member

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    Since you have a constant cel from the other issues could you have a new code thrown without knowing?
     
  7. 1999BlueTahoe

    1999BlueTahoe TYF Newbie

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    Doesn’t seem like there’s a vacuum leak but definitely could be. Truck idles fine and seems to pull just fine. Only weird thing it does is not dropping RPM when I left off the gas while in motion. I haven’t really played with while parked and will mess with it. I feel like it revs and drops RPMs pretty normal in park. Had some people on fb mention cleaning the throttle body and MAF sensor. Will look into that as well. Thanks again.
     
  8. 1999BlueTahoe

    1999BlueTahoe TYF Newbie

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    I haven’t ran codes since I first bought it but this issue I have been experiencing since its purchase. Not to say it has t thrown any other codes though. The truck needs lower ball joints on both sides so I don’t drive it much at all, waiting on a friend to help me out with that project and hope to get it done this week/weekend. Ball joints don’t make any noise while driving but definitely feel it wonder around a bit. Haven’t decided if I want to go ahead and put cats back in or not. Just not thrilled with the roughly $500 muffler shop bill. I ultimately don’t mind the exhaust volume but can’t seem to find an answer if being catless is good or bad (other than environment stuff) and would like all my cels to go away.
     
  9. drakon543

    drakon543 Full Access Member

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    even buying a cheapest catted y pipe i can find for your truck your still looking at 290 bucks so 500 for the cat issue fixed and you didnt have to deal with it really doesn't sound like a bad deal to me. anyway running without cats wouldn't be a big issue anyway besides if your area requires cats at some point or emissions inspections. you could just go get a tune done at a local shop or contact black bear here on this site or thier own to have them tuned out. any codes relating to the missing cats will go away.
     

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