J3 AUtism - Has Anyone Had IT?

[sly]

I've had a cam and chip in & out of my AU about 5 times now. Each time it's in, the immobiliser starts randomly activating while driving. Not immediately, but after a few weeks. I get some warning a couple of days ahead of it starting - the speedo needle starts to shadow the tacho needle at low revs in neutral/park. Eventually the immobiliser (SmartShield) kicks in altogether and prevents starting the car conventionally (I have a workaround as the car is dual-fuel and the gas system is not affected by the fuel injectors being isolated).

I'm not sure if the J3 chip is entirely the problem however. I've had a scantool on the car a few times and the instrument panel refuses to provide diagnostic information. I have occasionally seen the speedo needle shadow the tacho without the chip in, and recently the car was immobilised for 3 days without the chip in but came back to life by itself.

The bloke I take the car to for scanning/restting thinks there may be a wiring issue, possibly with aftermarket wiring (LPG system and mobile phone stereo mute). An LPG tech has seen worn lock barrels cause the engine to immobilise while driving.

I'm thinking of replacing the dash loom and/or ignition lock barrel and/or PCM. I've already replaced the instrument panel, with no change.

Has anyone had the same problems? Any suggestions as to how I can test / fix the problem?