welcome to AO dude....if the diesel sound only lasts for a few secs on startup it probably is the variator and will not damage your engine, rather just reduce your top end revs slightly
the poor idle could be down to a sticky throttle valve
flats spots could well be plugs, did you have them changed at 60k ? or could be the MAF, even though it was changed it could be a "duff" one...disconnect and see if it makes a difference, if no difference it probably needs cleaning or changing...how to clean below:
Remove the MAF - undo the metal clips with a pair of small pliers or lever off with small screwdriver, undo the cable tie which keeps the connector cable tidy to the air duct.and then the connector remove the MAF.
There are 2 TX secrurits screws that clamps the sensor to the MAF body...these can be undone with pliers as they are not to tight.
Pull the sensor head out and stick the MAF body a bowl of luke warm water and slosh about...use a sponge to clean the inside of the MAF body but do not touch the Mesh. then put back in the bowl and leave for about 20 Mins...
To clean the sensor head you need anti-static cleaner from Maplin or any radio hobby store..
Spray liberally all over the head......
You will see a channel in the sensor head, and will notice a wire running inside....you can clean this with a cotton swab with cleaner applied.....don't go to mad just apply gentle pressure.
At the side of the sensor is a metal plate within another channel...you can clean this using the cleaner and some tissue, wedge it in the grove and slide in and out....you can use a small screwdriver to exert more pressure to clean the plate and the edges.
The sensor heads..electonics is sealed so don’t worry too much...but still be careful.
When this is done....rinse the sensor head under luke warm running water from the tap and just cover the top part of the head where you have cleaned...
when done remove the MAF body that was soaking, test the mesh for cleanness with a cotton swab, if still dirty use the anti-static cleaner to clean more..and re wash in luke warm water.
Lay both the sensor and the MAF body...on a tea towel on a radiator to dry naturally...
Re-Fit the MAF all back together and put back on the car.
all the best