ignition timing using data scan


MOT time soon so I thought I'd look at the base ignition timing. Using Datascan1 i had a look at it. I can get the idle to about 1050, now when its this speed the timing is at 10 btdc. With the idle at 1200 odd the timing is 20 btdc. If I remove the tps and rev to over 3k a few times the idle goes to about 1050 while the timing on datascan is 20 btdc, which is close to what timing light says although the light looks like it is just before 20 btdc. Is the fact that the idle is not below 1000rpm giving me dodgy values for the timing?

Also the aac value is at 8 if i put it to 2 it makes no difference to the idle, if i move it to 30 i can get the idle to increase. What value should i be looking for? Must be a vac leak somewhere but god knows where......