I have a Yamaha T60TLR manufactured 03/2006 with idle problems for the last 6 months. Initially it was only idle rough after it was warm. Engine would stall after going back to idle after running in the 3000 to 4000 rpm. This made docking a fascinating exercise that tended to exhaust my knowledge of 4 letter words.
Steps taken
replaced the spark plugs
replaced injectors
tested compression
replaced the low pressure fuel pump twice
rigged a gravity fed temporary fuel tank
replaced all fuel filters at least twice
tested individual injectors after replacement
tested spark plugs and coils
tested for vacuum leak using propane
tested high pressure fuel pump pressure
replaced thermostat
replaced Idle air controller with non OEM part
Gave up. took boat to a shop that said IAC was the culprit which they replaced with OEM part. They charged me one arm and two legs but said everything was fixed.
Motor idled at slightly higher rpm and ran rougher above idle.
I bought a diagnostic computer. Discovered the IAC was not changing with throttle position. Followed wire from IAC and discovered it went forward to the helm where it terminated in mid air. Used many 4 letter words.
Hooked IAC to engine computer. Was able to watch IAC respond to throttle changes using diagnostic computer. Mistakenly thought problem was solved.
BUT... idle now surges roughly every 3 seconds. Rpm increases by about 300 then falls back to baseline.
changed out fuel lines, and fuel filters (again) rigged gravity feed (again) swapped out low pressure fuel pump, used propane to look for vacuum leak.
Engine still runs like a champ at rpm above 2000. Occasionally stalls when throttling back to idle but commences surging at anything below about 1200 rpm.
I found someone had posted a similar problem with a honda and it turned out to be an O2 sensor but there is no catalytic converter on this engine so no O2 sensor.
I very much appreciate any ideas that anyone has on how to proceed.
Thank you
Steps taken
replaced the spark plugs
replaced injectors
tested compression
replaced the low pressure fuel pump twice
rigged a gravity fed temporary fuel tank
replaced all fuel filters at least twice
tested individual injectors after replacement
tested spark plugs and coils
tested for vacuum leak using propane
tested high pressure fuel pump pressure
replaced thermostat
replaced Idle air controller with non OEM part
Gave up. took boat to a shop that said IAC was the culprit which they replaced with OEM part. They charged me one arm and two legs but said everything was fixed.
Motor idled at slightly higher rpm and ran rougher above idle.
I bought a diagnostic computer. Discovered the IAC was not changing with throttle position. Followed wire from IAC and discovered it went forward to the helm where it terminated in mid air. Used many 4 letter words.
Hooked IAC to engine computer. Was able to watch IAC respond to throttle changes using diagnostic computer. Mistakenly thought problem was solved.
BUT... idle now surges roughly every 3 seconds. Rpm increases by about 300 then falls back to baseline.
changed out fuel lines, and fuel filters (again) rigged gravity feed (again) swapped out low pressure fuel pump, used propane to look for vacuum leak.
Engine still runs like a champ at rpm above 2000. Occasionally stalls when throttling back to idle but commences surging at anything below about 1200 rpm.
I found someone had posted a similar problem with a honda and it turned out to be an O2 sensor but there is no catalytic converter on this engine so no O2 sensor.
I very much appreciate any ideas that anyone has on how to proceed.
Thank you