Motorcycle Repair: Surging Idle and EFI (GSXR602), open loop system, gsx r 600

Question
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Followup To
Question -
I have a 2002 GSX-R 600 with 18k miles. A few months ago a surging condition would occur around 3k rpm then go away higher in rpms. It wasnt a problem really but now its much worse. Now if I hold idle steady around 4k the rpms will surge down to 3.2k-3k rpm. I would gas it again and it will hold at 4k but eventually (5sec) surge down to 3.2k  I have changed spark plugs since and now have white spark plugs indicating lean mixture. My previous plugs werent this white. I put back on my stock slip on and still no change. I had an extra ECU laying around so switched it out. Nothing. Its a open loop system with no O2 sensor in the line.I think this is right, meaning its a system controlled only by ECU and no mixture sensor like Lambda. I cleaned out my air filter and nothing. I got a clean air filter and nothing. I even got an extra fuel pump assembly from a friend for cheap (which was off of a bike with less miles then mine and cause I had a problem with my fuel reserve light not working) and nothing. its still surging down. My only guess is that my throttle bodies are waaaaay out of wack and need to be synched. My engine may be near its end of life..? Or Some other problem im not aware of? Oh i only use 87 octane. I have not washed the bike recently so water shouldnt be an issue. Oh and problem occurs in nuetral and in gear, especially under load.
Thank you for any and all help
Alex Majette
Sacramento,CA
Answer -
Hi Alex,

I suspect one of the following defects with the TBI:

1) Throttle body out of synch
2) Vacuum leak
3) Sensor problem

Respectfully,
Mark Shively


Thanks for the help. I purchased a relatively cheap vaccum gauge from motionpro then did the sync but that didnt do anything. Took my fairings off and realized i was really low on radiator fluid. So I think the bike was overheating badly and I may have fried the engine temp sensor. Does the engine temp sensor contribute to the ECMs controllability of air/fuel mixture.
Thank you again for your help
Alex

Answer
It's not directly related, though overheating may cause similar problems.

Be sure to purge the air from the cooling system. Check into a tool by MityVac called AirEvac. Cooling systems are designed to be air-free. Air in the system lowers the boiling point of coolant. Air trapped around the water pump may cause engine failure.

Check for vacuum leaks.