93 seville 4mpg rough idle black smoke

have 93 4.6 northstar seville sts, intermittently, idle will go rough, mpg display drops to 4, black smoke comes out exhaust and fuel gauge will start to drop. car has no codes on it, check engine light never came on. could it be injector sticking open, bad fuel pressure regulator or something else, looking for any suggestions and tips on troubleshooting this problem. thanks in advanced

My guess would be the FPR.

replaced the fuel pressure regulator and car is running normal again. thanks