I was having idle troubles and declining mileage on my 98 4.0L SOHC. I bought a can of CRC SensorKleen ( http://www.crcindustries.com/crcwebcanada/Portals/0/canada/sensorkleen%20poster.pdf ) and removed both the MAF and IAC and gave them a good cleaning. I disconnected the battery, let the MAF and IAC dry and reinstalled them. Took the truck on a 200 kilometer drive on Sunday and by the end of it it was idling better and the power all the way throughout the RPM range felt much smoother.

I would recommend the CRC SensorKleen to anyone who wants to clean the MAF or the IAC, by far the best $8 I have spent in a long time.