john, the symptoms i had was,,,, on tickover it was only running on 3 cylnders ,making the engine rock really badly, acceleration was very poor, and lacked power at all speeds,and very smoky
after checking everything i could think of i traced it down to a blocked injector by pulling off the plug on each injector while it was ticking over ,i did try to remove the injector but only got so far berore i realised it was going to need a tool to jack it out , so i decided to give the cleaner a try
it took a full tank of fuel with a full dose of injector cleaner (500ml stp £15) before it eventually cleared, ,( i now use it on a regular basis small dose ) , i now realise that these injectors are so fine , its essential that they are kept clean, im even considering giving them the shock treatment on a 6 monthly basis , try a bottle , you will also notice increased acceleration and a livley engine
best of luck