I've got a similar problem with a 1999 1.9dTi Laguna Alize. Whenever we drive in very heavy rain with lots of water on the highway the injector light comes on and the car goes to limp home mode.
The computer diagnosis is a fault with the potiemeter (which the Renault Dealer was quick to replace). This of course didn't solve our problem!! On one instance it stopped raining and the road dried out - the car appeared to dry out and continued a long 200 mile drive home without a problem.
Since then all the wiring has been checked, a plate was put under the
the protect it against water coming up from the road and the oringal battery has been replaced. The fault reoccured under the same wet conditions but the car was quicker to recover and drove though it. Again it stopped raining and it was fine. Today we started the car (no rain at all) and the problem occured immediately. This is the first time it has occured off a motorway and in the dry, however the January air is quite damp.
We sprayed WD40 on the battery terminals and revved the car a couple of times. It seemed to work fine after that.
Do you think this problem might be occuring because the battery is not sending enough power when you try to accelerate?? Could this be a similar problem?