I have a 3.8 in a 91 Cougar. I know this isn't a truck but you guys have been good to help me before. I bought the car and the original engine had blown a headgasket and the owner just dumped water in the radiator when it went dry (numerous times). I put a used engine in it and it smoked bad when we first started it - it looked like the engine we put in had a bad headgasket. The smoke cleared and the car ran great but started to idle real rough and I haven't been able to get it smoothed out. The car idles worse when cold compared to normal operating temp. Also it surges when driving between 30 - 45 mph and pulling roughly 1K rpms but runs out great with no problems at highway speeds. We have put roughly 2K miles on it and it hasn't used a drop of water or oil. I believe the exhaust system was full of water explaining the smoke on itinitial start up. One more item is the exhaust smells like wrotten eggs/sulphur. So, where do I go? Could it be the cats or the EGR valve? I am totally baffled by this. We have adjusted the timing and idle with zero positive results. Any help will be greatly appreciated!! Thanks in advance.