Indmar 5.7 Assault TBI high idle, hard start -- Solved

I've got a 2003 Supra SSV with the Indmar 350 GM TBI engine. Boat has been running fine, then last weekend I came back to idle after pulling a rider and the boat stayed up at ~1500 RPM. Verified that Perfect Pass was not interfering by loosening the servo cable, double checked that the butterfly was closing. Unplugged a few sensors and I could get it down to 1000, but not lower. Once the boat cooled down it became difficult to start. Required 3/4 throttle to get it up and running, but with lots of black smoke until it cleared up.

Checked for vacuum leaks by spraying carb cleaner around vacuum lines and gasket surfaces. It all checked out.

Turning attention to sensors, initial suspicion was the MAP sensor because when I unplugged it the boat seemed to behave a little better. Google convinced me to look at the IAC sensor. But, since I'm kinda doofy by late afternoon I wasn't paying attention and pulled off the TPS sensor. I happened to have an extra one laying around so I put that on there just in case. Lo and behold, problem solved.

Just wanted to share a problem & solution (for me, anyway) since I couldn't find any threads with this exact behavior.

You had an extra TPS laying around? Color me impressed!

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Originally Posted by CJD

You had an extra TPS laying around? Color me impressed!

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Ha - don't be impressed by my misguided troubleshooting attempts of my past. :)

I have a 2006 24ssv and the same thing happened to me. Went to pull a rider and idle jumped to 1500 and would not throttle up or down. I ran fault codes and it said pedal position sensor which is the sensor that connects throttle cable to perfect pass servo motor. That did not fix it. Ran to a local auto parts store and bought a monovalve which has the tps attached to it for an early 2000's GM vortec v8 engine from truck/suburban. Saved me $150 instead of buying from Indmar. Installed it and she fired right up, runs like a champ.

The TPS that worked for my boat was an AC Delco 19259452 TPS Kit with clips or Duralast TPS4270 Throttle Position Sensor. Just google that and plenty of options should pop up. The TPS is in the center right of this pic, under the air intake. This part appears to come off mid 2000's Silverado/Tahoes.

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