r32psi

can someone help please

timing was set with a timing light. but i had a scaner on it 2.when i hit the gas the timing drops so its not pinging if i set the timing at 15 degrees coughs and splatters

I recently got an r32 gtst and my timing's retarding to 1 degrees advance. from roughly 5000rpm to 7000rpm it bogs down. after 7000rpm it picks up again... if i turn the boost up which is only on stock boost it coughs and splatters at 5000rpm... ive got the timing set t 30degrees advance and it drives better at that. but timing still retards to 1degrees as soon as i touch the pedal. can anyone help me please????