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We’re using a GM HEI distributor, which is known to produce a lot of electrical interference at the tach output terminal due to the coil in cap design. Connecting the ECU tach wire required installing the supplied tach adapter/filter, but MSD makes a heavier duty tach filter (PN 8910, $42) that may be more effective on this type ignition. Any stray voltage fluctuations can be read by the ECU as a variation in throttle position, or rpm, so the ECU will add fuel, thinking you stepped on the throttle. This can cause an erratic idle. The last thing to do was to run the communication cable for the hand-held controller. It came up a bit short, so we ran down to Radio Shack and bought an RS232 extension cable, which worked perfectly.