Mitsubishi Repair: engine stalls when warm, vacuum leaks, incorrect fuel

Question
My problem started only this
morning, I installed a new muffler yesterday, had to spot weld it in
place, as they'd sent wrong muffler length I had to cut and spot
weld,I live in United Kingdom so just couldn't post it back,
disconnected the battery before welding, when I'd finished I ran the
engine to warm to check for leaks, them left it until today, took her
out for her Sunday run, went fine until she warmed up, when I braked
the engine failed, arrived at the shopping centre completed my
shopping and drove home without problems, arrived at my drive way and
she died as i braked on entering drive,checked her over,with manual in one hand couldn't find a fault,took her for a test drive,and she stalled at every junction, lights,etc. Help, should say she's a 1990
LeBaron with a Mitsubishi 3ltr v6 , thanks in advance.


Answer
Nigel:Don't think the new muffler has anything to do with this. Other when you put on a new one and now the car has another new problem. You did not put down the miles but a 1990 I would says is over 100,000. I will send you ideas I have but not sure which one it is. Idle Speed incorrect, fuel filter clogged or water and impurities in the fuel system, distributor components damp or damaged, faulty emissions system components(like maybe a sensor out or getting weak, can use a voltmeter to check things out. Faulty stark plugs and  vacuum leaks. It takes three things to make an engine run; air, fuel and stark. Hope this helps and good luck.