I have a 1.9d (non turbo) dispatch van that I use. Recently, at certain throttle positions, it seems like I'm loosing a little bit of power, this mainly happens at motorway cruising speed, in 5th (top) gear with a constant throttle position.
To put it into context, I'll be in the motorway, doing a constant 60mph, with my foot in a fixed position in the throttle. Every now and again, it feels like I hit a headwind, which slows the van down slightly. As soon as push the throttle down, it picks up again. It doesn't loose much speed.
When accelerating hard through the gears, it doesn't happen.
It doesn't happen when I idle the engine in the drive.
I tried priming the fuel system, made no difference.
I'm going to try changing the fuel filter to see if that makes a difference.
I'm thinking (aside from the fuel filter), it could be a sticky throttle cable, sticky throttle body, maybe a slight air leak in the system somewhere.
Does anyone have any thoughts or experience?
I've googled it and found a forum where someone describes similar symptoms which just seemed to clear by itself.