ok my R has most of the bolt ons out there as well as a V-AFC....when I bought the car it threw check engine for awhile then stoped when I got the V-AFC. now it's doing it again.....when I put in the clutch to roll to a stop at a light or something it will idle at about 3000 then drop to 2000 the 1500 then 1300 then 900....well when the car is warm and idleing sometimes the tach jumps from 900 to 1300-1400 and jumps about 200rpms and lops bad....when this happens the check engine comes on. any ideas?

 

my car does this too butnot so dramaticallly...it'll idle at 1,100 and then i wont do crap and it'll dip to near stallish 750 or so then after a while up to 1,100 again

 

see what the check engine light code is. Then maybe i can offer you a good
explanation for the problem