Problem with Monster when warming

[delimondo]

My hand-me-down 2000 Monster 900S ie is okay when it's cold but when it warms, it gets real messed up. Basically at around 4–5k rpm, it's fine, but when it drops down to idle, especially at a stop, it'll either die or stumble. I already replaced the fuel pump and filter. What else do I need to do? What am I missing out on?

 

[Joe Goldberg]

My hand-me-down 2000 Monster 900S ie is okay when it's cold but when it warms, it gets real messed up. Basically at around 4–5k rpm, it's fine, but when it drops down to idle, especially at a stop, it'll either die or stumble. I already replaced the fuel pump and filter. What else do I need to do? What am I missing out on?

It's either an idle control or a sensor issue. Double-check the TPS and clean the idle air controller if you haven't yet. Also, try to rule out a vacuum leak. You probably already know how to do that.

 

[ZackHacks_]

My hand-me-down 2000 Monster 900S ie is okay when it's cold but when it warms, it gets real messed up. Basically at around 4–5k rpm, it's fine, but when it drops down to idle, especially at a stop, it'll either die or stumble. I already replaced the fuel pump and filter. What else do I need to do? What am I missing out on?

Same suspect as @Joe Goldberg. That actually sounds like a classic case of an air leak or an issue with your idle air control valve. When the engine warms up, things expand, and a small leak can become more pronounced, throwing off your idle. I suggest you check your vacuum lines, intake boots, and areas around the throttle bodies for any cracks or loose connections. You can use a good spray with some carb cleaner to help pinpoint the leak while the engine is stumbling and if the idle changes. If not, cleaning or replacing the IAC valve would be my next step.

 

[duca.ster]

Check your idle control and throttle bodies, those bikes are picky about sync and TPS settings. Could also be leaky intake boots or sensors acting up once warm

 

[angelparreno2455]

Check your intake air temp sensor as well. But yeah, the IACV could be the most common cause for this.