5.3 L Missing and Rough Idle Intermittently

I would check for unmetered air getting in. Look for cracked or missing vacuum lines

If it is idling like it was before the inj were replaced then you have fixed the wrong problem the ethonol doesn't damage injectors you probably have a spark plug wire that is bad or a coilpack is bad or you have a fouled spark plug? A compression test can tell you of any problems with the valves! The injectors are designed to be compatible with flamible liquids ie gasoline or alcohol! I have been a mechanic for 23 years and have never seen inj fail due to alcohol in today's gasolines! You might have been scammed? Anytime you have repairs done request your old parts to be returned to you! You might have to take the mechanic who claimed he replaced your inj to small claims court! Try replacing the plug wires and the spark plugs first if no change then get carburetor cleaner and with the engine running spray the inside of the throttle body where it is black with the throttle open and engine rpms increased if that doesn't change it the coil packs might be going bad there are three so buy all three as a set so you don't have to change them at different intervals! Depending on mileage the timing belt is reccommended to be changed at 150,000 miles the spark plugs are due at 100,000 the coil packs should last over 200,000 miles so I'm guessing it is time for major preventative maintenance? The timing belt being worn can cause rough idle too!

was it running this way before you changed the plugs? just a shot in the dark here possibly a defective spark plug, rare but not impossible. if it was running fine before changing them. Other wise I would take it to autozone and pull codes if it is P0350 #5 misfire we would use the process fuel, fire and compression. is there any engine coolant around any cylinders? Have you checked the coil packs? could be a bad coil pack. if no evidence of fluid around them proceeded to check for spark, fuel then compression. post back results or new post with more deductions. iis it no spark no fuel or bad compression.

could be fuel , try a fuel addative , get one that covers the catalytic convertor as well as the valves , injectors etc,look for any signs of wear/damage to vacuum and air hoses

Could be too many things for a rough running engine. This could be the o2 sensor, air or fuel filter, injectors or even the coil packs. If there is a CEL blinking on the db, you should diagnose the codes to locate an exact issue.

Dont get another harness. If you are using Autozone supplied coil packs, the problem is most likely the coils from Autozone. I have went through this exact same thing before. I changed the coild because one had a burn mark on the boot between the plug and the coil pack. I noticed it when changing spark plugs. The new coil from Autozone made the vehicle struggle on take offs and idle rough and the vehicle had no power. I installed another coil from Autozone again which was supposedly a better model and costed more. The vehicle ran a little smoother but the rough idle and small misfire was still there. I installed another coil from the dealership and the problem was fixed immediately.
I also replaced one of the coil connectors for a different cylinder but only because i broke it when disconnecting the coil packs to remove the spark plugs.
And when I installed all my coils and the new one from Autozone, I used dielectric grease on all the connectors. But the rough idle and power loss was immediate following installing the new coil from Autozone.
Beware if you are using coils from another part store because many part stores get their parts from the same source.

everything unnecessary as the problem is the injectors /fuel pressure or injector wiring
run the fault codes first and save money

ROUGH IDLING CAN BE CAUSE BY MANY THINGS.I AM LOOKING AT LEAKING VACUUM HOSES OR INTAKE MANIFOLD GASKET LEAK.DIRTY FUEL INJECTORS AND WORN ENGINE VALVES WILL CAUSE ROUGH IDLING.ALSO LOW IDLE SPEED CAUSE ENGINE TO RUN ROUGH.

Hello,
I would check and find the dead cylinder(s) and determine if its spark related or fuel. You can do this by removing the plug wires one by one with insulated pliers. Note: Pull the wires loose first with the engine off and take caution not to tear the boots. If you remove the plug wire and here an arc snap noise and it doesn't change the way it is running you know 2 things you have spark and it's one of the cyls that are missing. If thats the case look for a lack of fuel or bad compression. The injectors If this is a Vortec early stile it will have popet style injectors. The popets plug up and cuse a no fuel situation in that cylinder.
Check it out and let me know.
Roy