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Q: My yukon is running like nthere is something terribly teribly wrong

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My GMC Yukon 05 model 5.3L was given to me by a friend because I had recently wrecked my 15 Silverado. I knew and he knew as well that the Yukon wasn't running very good. It would fire right up but it would idle as if out of time or something was stopped up. We put a scanner on it and we had so many codes pop up. the knock sensor code was the first one I tackled by replacing both knock sensors. replaced the intake gasket. I have put a new mass air flow sensor on it and plugs and plug wires.

after putting everything back together I cranked back up and it was running worst. clear the codes hooked it back up to the reader and had these 2 codes pop up. P0101(MASS AIR FLOW) even after replacing the old with the new . P0449(EVAPORATIVE SILONOID) I'VE GOT A BRAND NEW ONE BUT HAVEN'T REPLACED IT.

what should I do from here need help please point me in the right direction. What should I do next?

My car has 135000 miles.
My car has an automatic transmission.

A: The mass air flow sensor measures the speed...

The mass air flow sensor measures the speed of the air going into the engine. The P0101 code could be an electrical issue. The PO449 code is related to fuel tank emissions. Codes give you the area of a fault and does not mean that the component needs to be replaced. Both codes need to be tested with a diagnostic chart which is specific to the vehicle. If you need to have this checked by an expert, a certified professional from YourMechanic can come to your car's location to properly diagnose the Check Engine Light to have the issues corrected.

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