- Apr 10, 2016
- Campbellsville, KY
A friend's '07 Suburban (5.3, 184K) threw P0121 yesterday. Another friend who's plenty capable with all things post-2000 Chevy trucks scanned it, cleared the code, and sent him to me to clean the throttle body. No CEL when I got it, no strange behavior as I pulled it into the shop. Took the throttle body off the intake but left it plugged in (caught the carb. cleaner and goo in a container) thinking that would avoid having to re-learn the throttle body. Upon startup, idle jumps to 1,700 but doesn't immediately come back down, instead staying right there, then slowly climbing up toward 2,500. Plugged in the scanner to watch the data, played with it for a minute, then took it for 6-mile drive. Runs fine, settles down to idle when in gear, and doesn't jump up high when moved from drive or reverse back to park. However, just like clockwork, when I tap the gas pedal in park the idle jumps up again and doesn't come back down until I put it in gear again. Also, startup idle is still just as high. Data shows desired idle @ 650-700 and actual at whatever speed it's revving, most of the time being ~2,400. Just to check it off the list I pulled the connectors on the TB and gas pedal sensor, inspected and applied dielectric grease - no change. Still no CEL, either. Any wisdom?