1991 Jeep Wrangler Q&A
1991 Jeep Wrangler Question: hard starting then backfires when driving
Sounds like timing chain worn out and possibly jumped a tooth. and/or possible valve problem. Do you know how to check either of these? Do you have a vacuum guage? Have you inspected plugs yet to see if it's only one cyl. being affected or all? I know you said you replaced them , but that will give you some useful info. Reply to this if you want more tips. Good luck. I also noticed a tip below my response that mentions common problem with TPS. Best get proper diagnosis first before wasting money on parts. - ziptie12
The throttle position sensor (TPS) may fail causing intermittent drivability problems like hard starting, stalling, and/or hesitation when accelerating. A failed TPS will require replacement, p...