Engine Performance problem
1999 Honda Odyssey 6 cyl Front Wheel Drive Automatic 106000 miles
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When I start the engine it accelerates an desaccelerates repetdly from 1000rmp to 2000rpm

Hi jmlopez,

The engine idling speed is too high due to vacumn leakage or a loosened idle adjusting screw.

Check the ISC and the coolant hoses to it.

Low coolant level will also cause the problem as the ISC is not getting the correct temp.

Hi KHLow2008,
Thank you. I verify the ISC and the coolant level or leaks and found everything OK.

Today I scanned my Honda and pulled code P0505. Any ideas appreciated.

Hi jmlopez,

P0505 is a malfunctioning ISC.

How did you verify that the ISC is ok?

For this model if the ISC valve is short circuited and replacement of a new ISC still show the P0505 code, then you need to replace the ECM as well as the circuit in the ECM is damaged.