Help!

[6mmhunter]

I've got a NBS 2007 Chevrolet Silverado LTZ 5.3 L 4dr shortbox. Lately while cruising at highway speeds with steady throttle pressure it feels like a slight hesitation or miss. When accelerating harder it feels fine and at lower speeds it also feels fine. I just hooked up my live scan tool and took the truck for a short drive and got the following

 

Cylinder #1 misfires 5

Cylinder #2 misfires 5

Cylinder #3 misfires 8

Cylinder #4 misfires 3

Cylinder #5 misfires 4

Cylinder #6 misfires 1

Cylinder #7 misfires 0

Cylinder #8 misfires 2

 

While the check engine light never lit up it also noted 2 Engine Control Module codes

P0121 Throttle Position (TP) Sensor 1 Performance

P2119 Throttle Closed Position Performance.

 

Any ideas on where I should start first???

 

Thanks in advance for any and all replies.

[6mmhunter]

Nobody?

[00Silverado4x4]

I'd start with checking your fuel pressure to rule out the pump/regulator.

[sahls01gmc]

How many miles? What is the condition of your plugs & wires?

[Nick17]

you will probably need a new throttle body or you have an intake leak/air getting in thus creating uneeded vacuum the misfires you showed wont necessarily create the roughness if your misfires were 1,000 plus then it would be something to consider i would try a vacuum test

[6mmhunter]

The truck has around 115,000 miles on it and I was planning on starting with replacing the plugs. Should I test the wires first or just replace at this point.

Yeah I'm thinking I may need a new throttle body as well. If there is a vacuum leak wouldn't it run rougher at idle?

 

Thanks

[Nanotech Environmental]

you will probably need a new throttle body or you have an intake leak/air getting in thus creating uneeded vacuum the misfires you showed wont necessarily create the roughness if your misfires were 1,000 plus then it would be something to consider i would try a vacuum test

Not sure how the throttle body would be a culprit here. If it was, you'd have a symptom such as consistent misfires on all cylinders, not just some of them. Or worse. Unless I'm missing something?

 

Based on your scan results, the problems will more likely be related to injectors, wires, plugs or anything cylinder specific.

It could also just be bad fuel causing some injectors to become slightly clogged....

[Nick17]

I agree but it threw two throttle codes and I replaced the throttle body and fixed it usually it will cause roughness and I would also run rough if you have a leak my truck ran rough and I there was a crack in my intake manifold and I put a new one in so there are a lot of things to consider

[rjgti]

do a basic tune up, pull rail pressure, what are fuel trims, include short term also

[6mmhunter]

Okay so I replaced the plugs, tested all of the ignition wires (780-790 ohms all were in this range), pulled and cleaned the throttle body, cleaned the MAF sensor. The misfires are pretty much nonexistent now but am still experiencing the slight miss when cruising with light throttle pressure and the same two codes keep reappearing. Would replacing the throttle body be the most likely fix or is this something else? Thanks.

[6mmhunter]

I was in the garage today and turned on the truck ignition without starting. I could hear a rattling grinding noise coming from the engine compartment. When I turned off the ignition it did it again. I turned the ignition back on and put my hand on the throttle body and I think the noise is coming from it. With the issues I'm already having I think I'm going to buy a new throttle body. One question though is it worth the extra money to buy a AC Delco part or is any aftermarket throttle body as good? Thanks.