any gm tech need answers

[SouthSide1]

02 chevy silverado 5.3 98000 miles
miss fire codes, truck idles funky replaced plugs and wires no help,took in and had checked low fuel press so new fuel pump and filter worked finr for a day started truck today and back to the same shit. they tested the injecters and they checked out fine no leaks. truck runs fine while driving just idles funky has anyone came acros this at work and knows what the fuck is up w it any input would be greatly app. thanks aaron

[Yooformula]

I chased down similar issues and did the same fixits then ended up changing o2 sensors and cleaning the maf. SES light was gone then came back again but this time with evap and turned out it was a bad gas cap that constantly had frozen water on the inside of it. try to clean the maf then maybe swap some o2's if they havent been cleaned or swapped at all yet.

[stealthy1ss]

Also clean behind the butterfly on the throttle body. Clean it with carb and choke and a rag. When you start it up it might not want to run very good so give it a little gas. I think the part I am talking about is called the throttle plates but I am not 100% sure.

[Holeshot]

Check for vacuum leaks.

[BAD LS1]

This is something i bet that is making the fuel trims go ape shit or the MAF is reallllly dirty. Were the plugs black when changed by chance? Usually unexplained idle issues and poor overall perf is due to a new air leak AFTER the MAF or the MAF cross hairs have a 5'o clock shadow. I dont know if 02' k-trucks still had EGR or not? If the pintle in the EGR valve is leaking or the gasket took a shit too that will help dispense spent exhaust gases into the intake at idle and obviously exhaust has little to no oxygen available to burn again which will make it run like shit and misfire too.

[SouthSide1]

the plugs were really dirty yes the fuel trims wre way lean i think is what the scanner said and low pressure like 50 lbs w key on mtr off and it should be around 57 or sumthin so thats why john said it needed a fuel pump he ran it w the scanner on and it wasnt doing anything funky. so i picked it up and drove home w no issues started it up this morning and back to the same shit. it does have a kn filter but that been on there for 4 years and i havent had any problems so maybe it is dirty i dont know

[Coops Brother]

Intake gaskets between the heads and intake are leaking vacuum, does it run worse cold?
Yes? spray brake cleaner at gaskets, if the idle changes, there ya go.

[BigBlackZ71]

Fuel pressure regulator? I have the same truck and mine crapped out a few months ago

[BAD LS1]

But the FPR usually also causes longer crank to starts as the most obvious issue. 7 psi of fuel pressure diff is lower than normal yes, but its not going to kill off total performance overall, it will just show up in the trims where there is 25% leeway in either direction. The old CPI vortec motors however? yeah those need to have adequate fuel pressure or the popet injectors wouldn't fire or if they didn't wouldn't atomize for shit.

However if it is this inconsistent im definitely gonna lean away from any sort of intake gasket leak and more twoards some sort of false issue like a k&n that caked the maf cross hairs... Look at it with a scanner again, if the trims are higher than +10 there is something going on, and its dumping more fuel than needed to fix what it thinks is a lean condition but would end up being a maf calibration issue due to it being dirty. Too much fuel at idle definitely will make it surge!

[SLOWC5]

Quick check on the FPR is to pull the vac line off. Gas in the vac line FPR shot. I'm going with intake gaskets. PM me if you need it looked at.

jeff