2006 Chevy Colorado 2.8 4 cyl. Engine is surging under normal acceleration. It has about 85K.

Have you monitored the engine sensors when this happens, if not have that done.

probably your spark plugs or spark plug wires......
change spark plug and try it if surge occur
check air filter too

Are you sure you replaced the plug wires correctly? As for the engine noise, is it overdue for an oil change?

My first thought would be a vacuum leak in one of the hoses. Rubber hoses get brittle with age and even a small crack in a hose may cause surging. Happened to me in a Lumina.

CHECK AIR FILTER NEED CHANGING COULD BE CLOGGED OR CLEAN IDLE AIR INLET PASSAGES REMOVE IDLE SPEED CONTROL VALVE DONT SPRAY CARBURETOR CLEANER ON IDLE AIR CONTROL VALVE YOU WILL DAMAGE IT. AND USE CARBURETOR CLEANER TO CLEAN THROTTLE BORE AND THROTTLE PLATE FROM CARBON DEPOSITS MAKE SURE ENGINE TUNED UP YOU HAVE FUEL INJECTORS CLEAN NEW FUEL FILTER.NEW SPARK PLUGS AND WIRES IF ENGINE HAS 100000 MILES ON IT.

If your truck has the intak filter box on fire wall and air box over the valve cover remove it. remove the flex tube for the fire wall to the box ontop of the valve cover screw driver. Do the same to the throuttle bodody flex tub remove it as well Then there are two screws I think 12mm on the passangers side of the box. Pull away from t-body and up the coil packs are under the box. Simple remove one bolt from each coill and pull it up and out "do Not **** on the wires". Then pull the plug out and replace.there is a 3/4" blow back tube you will need to remove and put it back on after the pluges have been changed.

This is for the 5 cylinder 3.5 liter engine in the Colorado

1. The drain plug is in the middle of the oil pan on the drivers side.
Use a 15 mm socket or box end wrench to remove the plug. Drain
oil.
2. The oil filter is at the bottom front corner of the engine on the passenger side. Remove the filter. Try not to tip the filter when you
remove it so you don't get oil on other parts of the truck.
3. Rub a small of oil on the gasket of the new filter. Spin on the new filter, 3/4 to 1 turn past when the gasket starts to seat. Hand tighten
only.
4. Reinstall the drain plug. DO NOT OVER TIGHTEN OR YOU COULD
STRIP THE THREADS.
5. Add 6 quarts of oil to the oil filler tube located on top of the engine
in the front and middle of the engine compartment. It shows the location
in the owners manual. Install the filler cap.
6. Start the engine and let it run a few minutes to fill the filter with oil.
Turn off the engine and wait a few minutes for the oil to drain down to
the bottom of the engine. Remove the dip stick and check oil level.
Checking oil level is in the owners manual.

under the plastic in the center of the engine 5cylinder must be cold or can warp head use aintseize on new plugs check gap hope this helps

po 305 is cylinder 5 misfire detected. I would check the plug wire for starters

if you have a owners manual read it. try coloradofans.com website and search the forums. i think johnny5846 is right if you don't have a DIC (driver info center). i believe you use the DIC(tripodometer). i don't know the sequence off hand, you can also you can change your lock settings and alarm settings, etc. with the DIC.