ok guys heres the deal, i'm dealing with a 91 RS 6 cyl that belongs to my GF, it had been overheating constantly she asked me to look at it, the radiator was leaking bad, so we replaced it, it still would over heat, just not as quickly, so last night we replaced the the thermostat,i'm not sure what the stocker is but we used a 180 degree thermostat, it seemed like the next thing to try since the fan was working ok, the thermostat was kind of a pain we ended having to take the throttle body off since it was right under it, anyway we get it all back together she goes to drive it today and well, it stayed cool at all times however now its stalling at idle untill it gets warm, then its fine. and the service engine light is now on. i checked the codes and it flashed 13 and 15, any ideas guys? let me just go on the record and say stay away from a 91 6 cyl RS, its like this every week with this damn car, thanks for the help