Land Rover Repair: Rough Idle and de-coke cylinders/valves, gm parts, hi john

Question
Hi John,
Been reading through your posts and have a couple of questions re my 1995 V8, 3.9L Disco.

I note you recommend de-cocking the valves etc with an additive - how exactly do you do this ?

Second is a rough idle, sounds common.  Will try put a sports coil in, replace fuel filter and air filter as a starting point and check the resistance in the leads.  Any other simple (and cheap) tricks I might try ?

many thanks
Dave

Answer
De-coking with an additive refers to the use of GM Top Engine Cleaner.  Directions are on the can, available at any GM parts department.

As to a coil . . . I recommend you skip the "
sports coil."  In a car with electronic ignition the likely result is a burnt out module