http://www.peachparts.com/shopforum/showthread.php?t=289982&highlight=cis-e+tuning

This should be good reading after reading doc's post. Make sure you read all the way to the end.

EHA varies pressure and cuts fuel under no throttle coasting above 1000 or so RPM. Overall you are delivering too much fuel, but you can fix that with adjustment. As doc pointed out, it could be as simple as an O2 sensor, but as he also pointed out the system is mostly mechanical and decades old. The good news is that you can fix it.