Rough running
 

So I had to leave my 964 cabriolet out in the pouring rain for 3 months. When I came to bring it back into my garage everything was soaking (inside and under the bonnet). Got it running eventually but now running rough on start-up. Have found that if I remove front right top spark plug lead and put a plug in the cap so you can see it sparking, the engine will fire up and run smoothly! Has anyone any ideas as to why when you disconnect the top plug the engine then becomes smooth? Have replaced the top plug, replaced fuel and filter. Remember, car drove out of garage fine but 3 months later and after getting pretty wet, now running rough!!

Hello,

1. check dist for broken belt or moisture inside

2. Possibly , when you moved the plug wire to the independent plug the wires are no longer arcing at wrong time/place? Since it is a dual plug you are probably still firing that cylinder correctly with just the other plug.

Start the car in the dark and see if you can find any arcing. use something that doesn't conduct electricity to move the wires around a little while running.

good luck !