High idle problem with solution
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
High idle problem with solution My 98 Camaro with a LS3 swap recently developed a high idle problem during a long commute to work and made the drive pretty miserable. (I'm already dealing with a slipping clutch)
Car has been tuned correctly, perfectly fine DD winter/summer for past 3 years 4 years since LS3 swap. Idle set to 850, IAC counts in the 50's life has been good, so a high idle out of nowhere is weird.
On start, idle would be fine, you can turn AC on off and no worries. Hot/cold start seemed ok. It was after you started driving idle would go nuts. Relearn of idle failed to fix it, small adjustments in tune failed to fix, idle "reset" using hp tuners to monitor the IAC to get it to drop in value failed to fix it. It would read 50's on start idle, then when it was acting up, shoot up to 120+!
I cleaned the TB, lubed up everything, gave the TB passages a good cleaning, cleaned up the IAC and still nothing.
My only clue was an off blip of a TPS low voltage SES light during 1 of the relearn sessions where I unplugged it, it was inconsistent, but I did see it twice. In HP tuners, logging showed the TPS at proper voltages and reading 0 up to 100% fine.
I swapped out the IAC thinking it was faulty/skipping a gear who knows. This did not fix it.
It was during a longer logging session that I finally noticed a 'spike' of the TPS. It was only visible during a quick throttle transition, like blipping the throttle, it showed in the log as a no voltage reading and 0% throttle then showing the correct TP reading. It was not enough to trigger a code during driving.
Replaced TPS, did relearns and life is good.
TLDR version, TPS causing some faulty readings can cause high idle, my old IAC is now a spare and the old TPS is trash. I suspect the internals simply wore out after 19 years. It was the stock original TPS and IAC for me.
Car has been tuned correctly, perfectly fine DD winter/summer for past 3 years 4 years since LS3 swap. Idle set to 850, IAC counts in the 50's life has been good, so a high idle out of nowhere is weird.
On start, idle would be fine, you can turn AC on off and no worries. Hot/cold start seemed ok. It was after you started driving idle would go nuts. Relearn of idle failed to fix it, small adjustments in tune failed to fix, idle "reset" using hp tuners to monitor the IAC to get it to drop in value failed to fix it. It would read 50's on start idle, then when it was acting up, shoot up to 120+!
I cleaned the TB, lubed up everything, gave the TB passages a good cleaning, cleaned up the IAC and still nothing.
My only clue was an off blip of a TPS low voltage SES light during 1 of the relearn sessions where I unplugged it, it was inconsistent, but I did see it twice. In HP tuners, logging showed the TPS at proper voltages and reading 0 up to 100% fine.
I swapped out the IAC thinking it was faulty/skipping a gear who knows. This did not fix it.
It was during a longer logging session that I finally noticed a 'spike' of the TPS. It was only visible during a quick throttle transition, like blipping the throttle, it showed in the log as a no voltage reading and 0% throttle then showing the correct TP reading. It was not enough to trigger a code during driving.
Replaced TPS, did relearns and life is good.
TLDR version, TPS causing some faulty readings can cause high idle, my old IAC is now a spare and the old TPS is trash. I suspect the internals simply wore out after 19 years. It was the stock original TPS and IAC for me.
