May also run the car low on fuel(something I dont do normally) and put a couple of bottles of cleaner additive in, any recommendations on make?
When I drove my 125k miles 159 from Reading to Edinburgh it returned 41mpg driven at about 75mph constant. Seemed not too bad but I had just got out of an Audi 2.0tdi A4 which had returned well over 50mpg over the same roads.
I've used BG244, paying attention to making sure the tank of fuel you have it in lasts for at least 5-7 days (longer is better still). I've run a bit of 2-stroke oil (at 150:1 ratio) which reduced noise but didn't improve performance noticeably, and I've also used Redex diesel system cleaner on two tankfuls (again, leaving it the tank as long as possible)
The last thing was a cleanup of the intake system using a couple of aerosol cans of intake cleaner (some soaking for a couple of hours, some sprayed in the intake with the engine running)
Each of the abov steps made some improvement, either in better pickup, a faster response to pedal input, more noticeable torque and better fuel economy. Trying hard I can now manage closer to high 40's mpg and have betterperformance when needed.
knowing these cars issues with choked inlet manifold, for the cost of a few pounds of intake cleaner I would give tht a try first and foremost. Using an additive at the same time won't hurt either, just leave it in as long as you can do.