Here is the low down. I bought a 91 rs with the 3.1, bought it from a friend as a project. Funds dried up so i'm trying to sell it. I thought I would do a tune up on it before selling. When I got it, it had something that you could hear in the exhaust. My friend kept saying it was a misfire, so I thought id do the tune up. I changed the cap, button (or what ever its called), plugs and wires. Now it before it would idle good and run good. I couldn't ever hear a miss up by the engine. Now it still idles good, but at a high rev there is a loud pop around the fire wall and a light puff off some light smoke. I figured there is a bad doughnut gasket and the popping is unburnt fuel igniting in the exhaust. I still don't hear a miss. So here is my actual question. Is the popping in the exhaust bad. I noticed when I changed the plugs the further back I went the stronger the gas smell got on the plugs. I didn't smell anything from the cylinder itself and the plug wasn't soaked in it either, it just smelt really strong. Also what could be the cause of that as well. I'm hoping its nothing to expensive so I can sell the car.

 

Does it sound like it is inside plastic. If so the timing could be off and backfiring through the intake. That would also make it idle high too. All you would have to do is reset the distributor to base timing. If it is still making that popping noise it could have a leaking injector that makes it run rich and like you said when it gets hot it could ignite it.

 

It sounds like its coming from the back of the motor...sounds like you threw a fire cracker down besides you. I don't see how it would have changed the timing since the rotor button just lop on and off..but it might have. But as far as I know it never did it till after the change and it still idles fairly smooth. Ill check it out tonight and run it up and down the road abit.

Edit: I belive I have it figured out, thank you for your time and help