2001 Volkswagen Beetle problem "syndrome"

2001 Volkswagen Beetle 4 cyl Front Wheel Drive Manual 235k miles

I have a 2001 VW Beetle TDI with a syndrome of recent problems. At idle the RPMs wil sometimes increase approximately 300 RPMs. Sometimes it will increase and decrease the same amount rapidly, increasing and decreasing. Also the glow plug light stays on 5-6 seconds at starting and the engine revs when cranked after this long episode. These do not always happen but happens quite often. The dealed replaced the EGR valve and cleaned the intake but the symptoms persist. Any ideas?