Check Engine Light

Hi there...
Sorry new to this, this is my first diesel and car this size.

Just a brief description.
Two days ago I bought a Nissan Primera 2.0 GX TD

Now I notice the check engine / engine maintenance ligt comming on when I release the gas pedal in the car. Not all the time not continuous but just enough to get me worried.

Found a thread yesterday stating tha the ODBII could be trigered by a fuelcap that is not properly seated (so i took it off and seated it again absolutely properly) And for the first 35 miles I tought all was ok but...going downhill (slight slope) adjust my right foot and there it was again.

Called the garage where I bought it (from a private seller but they serviced it the last couple of years) and they tell me not to worry, however I am not fuly confident...those indicators are there for a reason.

This flashing can occur in any gear in at any speed, is not related to clutching (it seems) and so far In between 2200 and 2800 RPM (at any point in between) There are no weird noises comming from the engine, and stationary the engine sounds good . (Its the first time I drive diesel so the "extra" noise at low speeds (<30Mph) is normal I figure)

Is there any serious damage I can or am doing to the car by driving it?
Its a bit dificult to walik into a workshop with this problem at this stage, or has anyone experienced anything simmilar?

I also have a Primera 2.0 GX TD (1997) I'm having virtually the same problem - When driving and i take my foot off the accelerator it feels like the revs stick for a second and then drop, the engine check light comes on, I then get a loss of power for a random amount of time - i have found if i depress the clutch the light goes off and all is well again. I have read that a lot of problems stem from a faulty MAF sensor - but haven't found a problem that matches mine (until now). Have you solved the problem yet?