My 1999 3.0 S-type Has had running Problems For around 6 months.
The symptoms.
Hunting slightly at tick over 800 RPM
after acceleration the revs drop to 1500 for around 20 seconds before dropping to 500 then back to 800.
If performing a manoeuvre i.e 3 ppoint turn the engine will die just as your about to put it in reverse. (about 60% of the time)
very little tick over power,


What I've done so far.
Changed Spark plugs and Ignition Coils (brisk plugs and motorcraft coils)
Changed Air filter (K & N replacement element)
Cleaned Breather pipes
Cleaned Throttle body
Cleaned EGR System


Im not getting any fault messages or engine lights




Can anyone help?

 

Firstly, welcome to the forum.

My S Type expertise is limited at this moment.

Reading carefully your "done so far", I am questioning the infamous 90deg elbow in the lower section of the "V", under the lower inlet manifold. Many, many threads on here about it and the issues it creates.

I am about to do this to both ours, and I believe fun is about to be had.

Others with significantly more experience will come along sooner or later.

 

Probably will be that. You could read OBD LTFT values and would probably find you have a slight air leak all the time then what happens is it cuts out because there's a sudden air leak.

 

+1 to air leak.