Engine idles rough and scan tool indicates that load percentage jumps to 100 while idling while in gear.

superdave160 · August 16, 2023

2017 Silverado 4WD with 5.3L engine and 6 speed transmission. Had mechanic remove DOD system, installed new camshaft and lifters and everything else that goes with the DOD delete process. New plugs, new air filter, new throttle body. Occasionally throws P0506, engine idle speed too slow. Engine has been idling rough since I got it back. It often dies when maneuvering around parking lots, or when I'm trying to back my camper into a site. I often have to hold the brake to be able to increase the RPM while backing in order to keep it from dying. Found a couple vacuum leaks and that made it run better, but still not right. Had torque converter replaced with one that has a higher stall speed, no change. With the truck idling, the RPM fluctuates between 550 and 800 RPM. Using my code reader, the load percentage runs in high 20s when idling. When I put the transmission in D and hold the brake (not pressing on gas pedal), the load percentage goes up a little, then intermittently shoots to 100 percent and then back to high 20s. When this occurs, the RPM drops and the timing drops to near zero.

What could be causing this? Any help would be appreciated.

Edited August 17, 2023 by superdave160
typo

rav3 · August 17, 2023

Just curious about your truck.

Mileage now?

Mileage when DOD deleted? Why delete it?

Mileage when you replaced torque converter?

Why did you have

Almost sounds like your torque converter is locking up for your load change, but I'm no expert on that.

Is your oil pressure staying consistent?

Are you the original owner?

Edited August 17, 2023 by rav3

superdave160 · August 17, 2023

2017 Silverado, now with 48,000 miles. Bought it new. DOD delete done at 40,400 miles. Nothing was wrong with the truck, just wanted to get rid of the garbage before it caused a real problem. Thought torque converter might be causing the idle fluctuation and wanted to replace the poor quality OEM converter with a more reliable one. New converter has higher stall speed to go with the bigger cam. Oil pressure does not appear to fluctuate and is still in the same range as it was before.

superdave160 · September 24, 2023

Just to close the loop on this, I believe that my issue is with the EVAP system. I disconnected the fuel vapor line from the EVAP vent valve on the intake manifold. I then capped the port on the valve to seal it off. My issue seems to have disappeared. I'll drive it another week or so and, if it remains gone, I'll try to figure out what is wrong in the EVAP system.