Folks my 1999 S type v6 has developed a quite pronounced misfire which kicks in between 40 and 50 mph. Idle is uneven as well, car was serviced recently with new plugs, air filter as well. I put redex in and took the car for a 60 mile run it seemed to help initially but symptoms have returned. The car has only 50,000 on the clock and was parked up for quite a while. Any help greatly appreciated. Only one code on local mechanics diagnostic tool, saying cat not operating fully. He didn’t think that was an issue and thought it be a coil pack issue and Cheers Norman

 

Get an OBD tool with live data such as an elm327 (wifi for iPhone, BT for Android) and look at fuel trims with a hot engine at idle.

 

Yes we need to see the codes Get them if you can.
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