shouldn't though when I converted my cars to 4 wire I grabbed a 4 wire plug setup from the J-yard and soldered the 4 wire plug to the stock O2 signal wire, then ran the heater and grounds to the appropriate places. You need to solder the grey wire at it's connections all the way to the battery connector. The sensors operate on just a 0-1v scale so every little bit of voltage loss affects how rich or lean the car runs.
Though it doesn't sound much like an O2 issue, more like base idle isn't set properly, but hard to diagnose without hearing the car.