01 Chevy z71 ext.cab 5.3L 210,000 miles.
MISSES and KNOCKS in COLD TEMPS

(American model o2 sensors on candian model truck?)
Truck plugs are square and grey. Plugs I replaced with are square and black. Does that mean my truck is Canadian model?

Bought the truck 3 years ago and truck ran like a top. 2 years later after a lot of farm work the truck started getting bad mpg. (Service engine light was always on). When I cranked the truck in the morning between 50-70 degree temps it would miss and knock a lil bit but idle fine after a min. In colder temps (5-40 degrees) it would idle up and down and sputter and miss and die if I did not rev up to 2000 rpms and hold it there for a few moments till idle w/out dying. Once I drove it would still rev high and have a miss to until I drove a 2-7 mins down road. Then would run fine driving and idling. Had codes ran by autozone. Replaced all spark plugs and wires. New o2 sensors behind catalytic converter. (Only ones I was aware of at the time) and used some mass air flow cleaner to clean it. Replaced in line fuel filter. Didn't change a thing. Year later I'm changing my oil and knocked some mud off my exhaust and seen two more o2 sensors behind manifold. So I replace them. Then as I'm replacing I learned my sensors I'm taking out don't look like what I'm putting in and plugs are both square but different colors. I put em on anyways. Ran perfect during summer temps but in winters temps it runs like it did before I done any work to it. Please help!! I have learned to research before I tackle minor mechanic work again. But I can't find anywhere why it only does it cold and runs fine after motor and everything warms up.

 

Not sure what you mean by "misses"?

To answer your question on the "knocking" its called piston slap. Rings on piston shrink and expand after its warmed up. Just look for Piston slap or noise during idle.

If you take it to a dealer they will say it too or maybe just BS you and take your money. Have a 00' Silverado Ext Cab does the same thing in colder months. Never hear it during warm weather or after warming up.

On the case of suffering MPG's idk. MPG suffers in city and constant stopping and going, trucks run better on HWY even with a load.

 

Idle air control valve??

 

Nope, its the design on that year model truck. Dad has 06 Z71 no noise. Cousin has 01 year older than mine does the same noise during low temps. I was hell bent on finding a fix but its just the design flaw.

2000 Silverado - "Piston Slap"