hello all.
so my roughness at idle while in drive and stopped is still there, but ONLY happens after the truck has warmed up to normal operating temp. volt gauge in dash moves when i can feel and hear it stutter, but per my scanner the volts dont actually change. upon leaving a stop the engine kind of misfires until i get moving then its fine.

just went on small highway (45mph) and it stuttered while going up a slight incline and didnt wanna move.

spark plugs and wires?

the rough idle while warm i was thinking is bat cats since those have to warm up to be effective, and this only happens when its warm, but im probably wrong.

codes are as follows"

P0171 system too lean
P0174 system too lean
P0420 catalyst system efficiency below threshold
P0430 catalyst system efficiency below threshold

since this is a 2000 suburban w/ 295k miles(mostly highway), im assuming the cats have never been changed out. i dont need them for emissions with it being a 2000, so if i have them cut out and a straight piece of pipe welded in, besides getting a check engine light for the rear O2 sensors(which i can remedy with spark plug non foulers) and maybe some fuel economy changes, what side effects would i be looking at?

i just dont want to get stuck stranded somewhere with my 6 year old son.

unrelated: damn blower motor chirps and whines like a bastard when i push the brakes and also when i turn right more than when i turn left.

things i have but have yet to actually replace: serpentine belt, fuel filter, front pads+rotors, all probably not causing the issues.

things i know i need to do: valve cover gaskets

 

the lean codes is where you should focus, check fuel pressure and volume. Intake manifold gasket vacuum leaks are pretty common. Do you have access to a scanner?

 

possible vacuum leak... could be intake gaskets. don't worry about cat codes until you resolve too lean codes.

 

i have a wifi obd2 adapter and the obd fusion app on my iphone so yes i have access to a scanner. the thing is, those lean codes came up once before, and they went away when i replaced the air intake. now idk when they came back, because the cat codes set off the light, i just happened to be having some trouble today so i scanned it and they were there. the only reason i know the cats are bad is when i looked at the voltage readings on the o2 sensors, they didnt fluctuate like they should have.

as far as i know theres no vacuum leaks. i did get a ride to the parts store and bought plugs and wires, my buddy was going for a new battery so figured why not, i have no idea when the last time they were changed was.

 

i did some digging on the internet and mostly everyone else has this problem when its cold. strange that mine is when its warm and NOT cold, which leads me to believe its not the intake gasket, as im told when warm the gasket swells and eliminates the leak. the next thing is fuel filter, fuel pressure regulator, or weak fuel pump. i have a brand new fuel filter for the truck but i havent put it on yet. im not about to drop the whole friggin gas tank to change the fuel pump either. im thinking ill do a check to see if i can see any intake gasket leaks, and when i replace the leaking valve cover gaskets(whenever i get around to it) ill do the intake gasket at the same time. plugs, wires, fuel filter, and belt i bought already but havent changed out yet.

 

you need to see what your fuel trims are doing, watch the short terms at idle and held at 2500rpm they should read between 10 and -10.


Depends which 02 sensors you were watching and what rpm as to whether or not that points you in a direction, the front (S1) sensors should switch whether the cat is failing or not but as mentioned before unless they're completely clogged I would focus on the lean codes.

 

i will look at the fuel trims tomorrow while im at work for a 12hour day
i know the cats arent completely clogged as they were in my 97 tbird when i had it, when that happened the car went 20mph at full throttle and then died in a parking spot, wouldnt stay running till they were cut out.

 

Found the displays to monitor STFT and LTFT. At idle while temp at 185F the long terms stayed at 25%. The short terms mostly stayed in the -3 to +7 range. I didn't get up to 2500 rpm as it's almost midnight and I dont want my ***** neighbors hating me even more than they already do, but I held it at 2000rpm and it ranged from around the same, just a couple percent more on both ends. Around -5 to +11. I even monitored it while driving home from work, but I don't have any idea what I'm looking at or what those numbers really mean. I checked at idle while cold, and short term for both banks were around +9 to +15 but the issue I'm having is only when warmed up. Both banks are roughly equal during all of this.

 

i'd be checking for a vacuum leak, in a nut shell - numbers mean the ECM is trying to take away fuel (running rich) and + numbers mean its trying to add fuel (running lean). Idle is when you have the most vacuum in the engine so if its showing positive numbers at idle theres a good chance its a vacuum leak, if it was showing them while at cruising rpm i'd lean more to a fuel delivery problem. Normal range is 10 to -10 no matter what RPM the closer to 0 the better. In your case its sound like in open loop its fine and when it goes closed is when you start having issues. Fuel pressure, volume and vacuum leaks need to be your first checks

 

its been awhile but i finally got around to working on the burb. didnt replace intake manifold gasket, as when we sprayed around it the idle didnt change. i did replace valve cover gaskets so those shouldnt leak any more oil. engine looked extremely clean inside, cleaner than my friends vehicles which have half the miles. in doing this we found 2 vacuum leaks and fixed those, one was the boot that comes off the regulator and goes to the intake, which could have been causing all my problems. drove it back home last night, ran like a champ, CEL came on for both cat codes but i expected that as those were there before. so far no lean condition codes and no stutter nonsense, but it only really did it when it was warmed up, i should know for sure today.