Tachometer needle jumps high before stepping on accelerator pedal

2007 CHEVROLET TAHOE
70,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC
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MO-SAN
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Truck was running fine until I replaced a new flow master exhaust muffler a month ago. Everything was good until I started noticing low mileage on my gas. Check my intake filter and was not dirty, took out the MAF and throttle body, check not that dirty but gave it a clean with appropriate approve cleaners. Reset the vehicle ECM for memory flush out of old behavior to relearn new setting. Did the throttle body relearn procedure three minutes idle run, sixty seconds engine off, another three minutes idle run and idling was between half of 500 rpm and 1000 rpm. Now comes the trouble, when vehicle is put in drive the rpm needle suddenly jumps high before I get to even step on acceleration pedal and that never happened on old ECM brain. Drove the truck above forty five miles with lots of deceleration as said for throttle relearn procedure and nothing has changed. So, what am I missing and what should I be checking? Any feed back will highly be appreciated. Thanks
Nov 13, 2017 at 6:14 PM
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STRAILER
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Hello,

Usually when the tachometer jumps is because the engine is misfiring which back-feeds the electrical system. Has the engine been tuned up using AC Delco parts including the plug wires?

Here is a guide to help you get the job done if you have not done so:

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

Please let us know what happens.

Cheers, Ken

Nov 15, 2017 at 11:00 AM
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MO-SAN
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Yes Ken, the engine has been tuned up a little bit and somehow, I found my PCV hose with a crack on it. I have replaced a new hose and everything seems to be working right. Will keep an eye on to see how it goes. Thanks
Nov 21, 2017 at 3:40 AM
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STRAILER
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Good to hear, please use 2CarPros anytime we are here to help.

Cheers, Ken
Nov 22, 2017 at 10:54 AM