Today I took the stang about an hour north to purchase a Predator tuner and have my car tuned on the dyno. The tune installed, we ran a dyno run and I came out with 245/275 with a horrible air fuel ratio... It started around 15 until about 4k then fell to 13 at redline. After some adjustment he tuned it down a tad bit (not more than .5), and my numbers went up to 256/289. The A/F ratio however was still what he called 'dangerous.' We adjusted the fuel tables and couldn't correct the problem after 8 pulls. It then occured to me that I got this car used and it may already have a tune preventing us from changing things.. The tuner agreed and said he will have Predator send them a custom tune and I can flash it sometime next week. So on my way back home my Service Engine Soon light start's flashing.. Am i safe to drive for a few days? It currently has the predator tune running lean. Please bear with my inexperience.