it runs lean when you do it but i didnt have any problem, i had it slacked before and my mpg droped to around 30 for hardly any power increase. so i experimented , wound it up instead, pumped the tyres up to 40psi and did 560 miles to a nearly full tank call it 7 8ths if you will. i dont know the tech on it, just did the oposite of the tuning guide on club gti.