Our 2001 Sport (4.0L, 130K miles) developed idle surges of about 200-400 RPM and they repeat every 5 or 6 seconds periodically. It does this on P, N, or D. We hear a crackling noise during the surges. It does this with engine cold or hot. Car starts fine from cold every time. Should I just replace the TPS?

I also noticed the temp gauge never goes above 160 or so even after long drives (middle mark shows 210).. Not sure what type of thermostat the car has..do I just have a bad temp gauge?... cabin heater works fine although loud winding-like noises come from behind the panel when turning heater dial from hot/cold.

Thanks!