i recently installed a used engine. I have a 1994 honda civic 1.6L vtec and it has been reving about 2,000 rpm. After a couple of minutes it idles down to about 750rpm. When i press the gas while its reving up or when it idles down it revs up and down and goes nowhere. I also was messing around in the engine bay and wiggling the wiring harness near the distributor and it cuts off. someone please help.

 

Go over your engine installation. You could be missing a ground or plugs not mated fully, as I had missed one ground when I did my engine install on my 90 Civic. It was pointed out by one of members here.

Also make sure you have coolant filled and bled, as they say coolant level/temp has something to do with engine operation at idle.