Hi guys- I bought a "well maintained" 1991 cherokee for my son as his first vehicle a few months ago. running fine until we took it to the beack and he tore around the dunes for a while. It stopped running and only idled roughly for a few minutes each time I tried to start it up. net- net. Wewnt to 2 shops and replaced ignition wires, plugs, distr and cap, coil cps sensor, fuel filter. Now here is the mystery. It starts and runs fine in neutral and reverse, but when you put it in drive it still idles rough. You can drive it however. when you get into the higher rpms it smooths out. What would cause this problem only when in the forward gears?

 

I had one that done that to me somewhat similar issue. My issue was the timing chain. I thought it was a vacuum issue but after I replaced the timing chain it worked fine.