In the last 2 months I've noticed a marked drop off in power (top end power). Its not as noticable just driving the car alone, but with my big trailer, I used to be able to pull it happily at 60mph but now struggle above 40. On my last 1000mile trip at the outset all seemed basically ok though a little sluggish but over the outward 500miles the performance dropped off remarkably. I removed the air filter to allow me to get back and which improved performance, but it wasn't dirty/blocked etc- and its still not right. I usually get 25mpg when towing but have been getting 15mpg recently. The engine had a basic service in July (oil+filters) and after that was doing 39mpg on a long gentle run (w/out trailer) (the best I've ever got out of it) and even now the engine idles and runs very smooth and although near winter still 28-30mpg. Car has done 50000 miles. I have run a tank with cinjector cleaner recently too.
When you push the revs above say 3000, 1) you need to give lots of right foot and 2) its much more lethargic than it was.
So what may cause this? my thoughts are:
plug gaps widened? they are due for a change, but no misfiring though- always starts fine exhaust problem? no leaks and sounds just the same but wondered if some internal baffle may have failed Sensor gone off? perhaps a sensor is giving a strange reading making the mixture far too rich?
I'm taking it to the dealers to have a diagnostics check done, but I don't want the dealer changing and tinkering with allsorts unnecessarily.
Cliff