Does it happen when it's hot? The IMRC can play up as it's mounted just above the exhaust manifold. It's the black box that sits under the plastic shield in the engine (the one that says ST200 on it)

You can either just get a replacement one, or better still move it so it sits under the battery tray. You can get away with moving it without having to alter anything as the wiring will just about stretch that far. It's wiser to lengthen the wires though, and there aren't many so it's not a hard task.