Alot of people with 400's get probelms with the tick over, footwells filling with water and probally lots of other small faults. (below might help solve the probelm)
1: The probelm with the tick over can normally be sorted out by doing a number of things. Cleaning out the tickover regulating valve with Carb cleaner normally does the job.
Also cleaning out the crankcase ventilation valve with carb cleaner helps. If you havn't replaced spark plugs, HT Leads, Air filter or rotor arm for a couple of years this should be done.
In some case's on fuel injection cars the injector seals might be worn and will have to be replaced which is not a hard job to do.
2: The probelm with water in the rear footwells is a common fault and can be fixed by sealing the rear light clusters.
3: I recently had a probelm with the car juddering on fast excelleration this was down to the Turbo bypass valve which has a membrain in it and was damaged to check this simply remove the bit of tube that runs from the valve to the manifold at the manifold end and suck it, you shouldn't be able to suck any air and if you place you tongue on it when sucking it should stick to the tube.