I just noticed that I'm having this problem. 04 4.2 I6, noticed that the oil pressure gauge on the cluster drops to 20 then to 0 then back to 20 when parked/sitting at idle. Give it a little gas, goes right to 40. This is after the engine has completely warmed, driven 20 miles, plus 90 degree day here in Florida, noticed when I returned home. When the oil PSI gauge goes low, sets off the Check Gages light. No signs of anything wrong (abnormal vibrations, engine has enough oil, etc). How would I check the PSI, besides the PCM? Oil has about 2000 miles on it, per the sticker from the dealership, however the dealership didn't seem to notice the tread had worn off the insides of the front tires, so hard to trust them.