1997 Nissan Maxima car sputters, oil like flickers, temp ga

I have a 97 maxima and put a used engine in it after I blew my other engine. It is standard, and one time after downshifting hard and reving high the car started sputtering, and usually when it sputters the hot cold gauge flickers down toward cold, I've noticed sometimes when I hit a hard bump the gauge flickers as well. Sometimes the check engine like comes on and when it does it flickers very quickyl and dims in and out and I noticed the car sputters and jerks more when it is flickering, but is never a constant light. Also the car idles rough and stalls out sometimes and if it doesn't stall out the rpms go up and down acting like it will stall out, also the rpm gauge stops working at around 2000 rpms The main problem is the car sputtering and sometimes jerks really hard. Please help I will put whatever parts I need into it. I put spark plugs already.