The guy told me that he had taken it to a shop and that they told him the block was cracked. ....
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Ok, you know pretty much nothing at this point. It could be anywhere from simple ignorance, incompetence or laziness, up to hopeful charge for teardown/replacement.
And at 3 posts total under your belt you may not realize the perhaps best feature about this forum is the vast intel archived here. My guidance is fill the AF. It might take 5 start cycles for the light to go off - don't worry. Just get all the damn air out of the system. There's search for that. Get to AZ/O'R or Advance to read codes and deal with those first. There's search for every code you can think of. Then, attend to the thousand normal maint. and upkeep expected for a 20-year old car. Hoses, wires, plugs, sensors, grounds, fuel system, filters. There's search for all that. And learn all the acronyms that can cause headaches, IAC, FPR, TPS, ECT, EGR, ICM, IC, EVAP. Yep, there's search for those as well. Along with all that, there's numerous stickies on 'rough idle/running'. Search them all.
EDIT: Your last above noted. But all insight still holds. 1,700 not bad. I'd still establish what's really the issue before swapping the motor - even if free. You'd hate to do that if it was only a giant overheating that fried a hose/wire/component causing rough running.