I have a very tired 1990 YJ 2.5. It spent it's life as a pit vehicle at a sand and gravel pit in north Las Vegas. It has had runability issues from day one with rough idle, to very little power. I have changed the tbi injector, cps, tps as well as the map sensor, ignition module, coil, plugs, wires, cap, rotor, and egr valve. I just put a timing light on it to see where my timing was and at an idle it is showing 15 degrees btdc. Is that normal? Or is it possible the timing chain has slipped a tooth? As the idle increases it moves toward tdc and at about 15 to 16 hundred rpm it's at tdc. Any thoughts on loose timing chain vs. bad module somewhere? Thanks for any help.