Unstable rpms

[bobrx3]

Under close examination I finally noticed the lock tab on the electrical connector to the pump was touching one of the little bolt heads

I know exactly the connector to the pump that you mean. There's a bolt that gets in the way of the locking tab. I noticed it taking the connector apart, so I made a special note to check it when I reconnected it. Looks like it must be a common issue!

Headers and pipe connections are tight, so it's not that, but it's an interesting idea to maybe disconnect the O2 sensor and so make the system run open loop. It could be closed loop on partial throttle and open loop on WOT but I don't think that info has ever been provided. That's typically the way these things work though. I know the engine will still run with it disconnected but I haven't checked if it makes any difference to idle or higher rpm stability.

The other sensors aren't part of any feedback loop, so they shouldn't cause instability unless they are generating a noisy signal rather than a constant voltage. I think they are probably required for the engine to run though. Easiest way to measure them would be via the diagnostic port, but the signals could be monitored on an oscilloscope or even using a voltmeter once you can actually get to the appropriate wires.

All the fuel here is the typical 10% ethanol - or at least that's what the pumps claim. I've heard rumors that there's a marina with alcohol-free gas for boats not far from here. More expensive of course but it might be interesting to try.

I'm still hopeful of being able to connect to the diagnostic port. That's really the best way to look at this. If I can't get my system to work I'll have to talk with CSC about getting one on loan for a few days.

Most of all I'm looking for feedback on whether other RX3s do this. If they all do it it's probably a waste of time trying to eliminate it and it could just be a characteristic of this engine.