this was cause by lots of reason
if u install fuel regulator n u put very high presure will cause 2 rich nor ppl will put 3bar/42 psi
or u change higher/bigger cc injector
if u have this problem u have to go get some managment for your car
if u are running for OBD2 harness go for AFC/SAFC/AFC Neo/E-manage/power fc And +++.....
if OBD1 u can get all above or crome/uberdata/