Replaced the head gasket this past week on my friend's 92 Accord LX. Now we're having a problem whenever we try to start it. It starts, and then immediately the RPM climbs up toward redline. We shut it off before it gets there, so we're not sure just how high it's going to go.

TB is fine and not sticking. TB remains closed while the RPM climbs. Throttle cable looks good. I'm pretty sure I connected everything correctly.

I think it may be caused by the Intake Air Bypass system (the IAB diaphragm actuator moves when the RPM gets into the upper half of the tach) but I'm not sure why. I tried disconnecting the IAB electrical connectors, but there's no change.

Are there any ideas on what else I can check?