2013 Super Tenere with intermittent poor idling/stalling issues

[ddentrec]

Hi everyone.

Sorry for the long post - but have collated as much info as I can about this intermittent problem.

I have my 2013 Super Tenere owned from new. It has 30k miles and is completely standard. Garage stored. No corrosion. Immaculate condition.

The issue I have is intermittent poor idling/stalling:

- Issue started about a year ago.
- 99% of the time the bike will idle @1200 rpm fine. Engine smooth.
- Intermittently (~ once in 7 days) after a run and then coming to a stop the idle revs drop to 900rpm: engine very rough when idling. Then after ~5 seconds engine is suddenly idling OK again rock steady @1200 rpm. Sometimes the engine may stall with the throttle closed.
- Sometimes - twice a month ? - with a throttle grip fixed at a steady 2000 rpm - the revs will 'hunt' between 1800-2100 rpm. The the bike will then suddenly idle fine with no hunting.
- Am certain that sometimes when riding the bike the throttle is surging slightly when in gear but it's very slight and I think I'm imagining it TBH.
- Problem seems to be getting worse/more frequent.
- No codes. No Engine Management Light.
- Original ECU mapping. Unmodified all-original bike.
- No coolant loss or other obvious issues.
- Issue happens in hot or cold, wet or dry, weather.

I have ridden the bike with a range of diagnostic equipment connected. Diagnostic/fix attempts over the past year (none have resolved the issue) include:

- Yamaha throttle wiring harness modification for the TPS/APS corroded loom issue fitted (part no. 90891-30131). Was the first thing I read about.
- New DENSO spark plugs (old plugs had good colour)
- Fresh premium fuel
- New air filter
- New Yamaha fuel pump. Pressure is a good 50 PSI when issue occurs.
- New Yamaha coil packs
- New Yamaha inlet rubbers
- New Yamaha crank sensor
- New YUASA battery
- New fuel pump relay
- No inlet air leaks (smoke test passed)
- New engine earth cable
- New complete throttle body assembly & fuel pipes.
- New Yamaha injectors, injector seals, fuel rail & pressure regulator
- New Yamaha APS & TPS sensors. Correctly calibrated.
- New Yamaha O2 sensors
- Regulator rectifier output steady 14.6V with/without the issue
- Inlet & exhaust valves check OK.
- Compression check OK
- Fuel tank vent OK
- Crankcase vent OK
- Throttle bodies professionally balanced/checked (OK).
- All electrical loads removed - no change.
- Amp clamp on the battery did not show an open/short when the issue occurs.
- New air temp and pressure sensors.
- Wiring loom inspected twice for chaffing, loose connector pins.
- Electrical noise check with an oscilloscope - OK
- Exhaust back pressure/catalyst OK.
- Engine timing correct.

Any thoughts?

Thanks

Daryl

 

[Sierra1]

Pour the gas out and refill with fresh. Unless you drive it daily and it hasn't been sitting.

 

[Tenforeplay]

Fuel tank filter?

 

[ddentrec]

Fuel tank filter?

Thanks for your reply. New fuel filter came as part of the new Yamaha fuel pump assembly.

 

[ddentrec]

Pour the gas out and refill with fresh. Unless you drive it daily and it hasn't been sitting.

Thanks. New fuel already in place. Tank was drained too.

 

[Tenforeplay]

How was the exhaust back pressure checked? Could you somehow be able to tell if there was a rich or lean condition during the occurrence?

 

[Squibb]

It sounds like an Intermittent air leak, inlet side.

You have replaced the inlet rubbers, but was the balancing port cap replaced when the new TB/fuel lines were fitted? These crack up with age & usually leak when cold, but can self-seal once hot, so the symptoms go away.

 

[ddentrec]

How was the exhaust back pressure checked? Could you somehow be able to tell if there was a rich or lean condition during the occurrence?

Exhaust back pressure checked against a known-good Super Tenere by installing a pressure gauge in place of an O2 sensor - similar setup to checking if the DPF on diesel engine is blocked. Was thinking the catalytic converter had cracked but that does not seem to be the case. Cannot check the rich/lean as the issue is so intermittent. Spark plug colour is good though.

 

[ddentrec]

It sounds like an Intermittent air leak, inlet side.

You have replaced the inlet rubbers, but was the balancing port cap replaced when the new TB/fuel lines were fitted? These crack up with age & usually leak when cold, but can self-seal once hot, so the symptoms go away.

Thanks for the tip. New port caps came with the new throttle body assembly. But will double check...