94 ranger driving me nuts

I have a 94' Ranger 4x4 with the 3.0 V6. For the last three months Every once in a while you push the clutch in and it will rev way up until you let it back out. If you just let it rev it will go up to 3500 and eventually come back to idle, I also noticed that the battery terminal was loose and tightened it when it wouldnt start one day and the voltage guage was going crazy. I thought this fixed the problem but no such luck. The problem will last for about a week and usually go away for another month. It usually does it after you drive 15-20 miles. Sometimes when you start it warm it will not want to idle down like you are starting it cold. I have had it to the garage and they replaced the idle air control valve with a used one and reset the idle. They cant really do a whole lot though becuse it has never done it to them. Other wierd things is that if you shut it off and srart it again it will be fine for a little while, and the temp guage really never goes very but it makes good heat. Also yesterday I went 100+ miles and the check engine light flashed on and off half a million times. It will only stay on for abut 20-45 seconds maybe a minute, is this long enough to save a code? Any ideas about this problem would be much apperciated. Also they dindnt think it was the TPS since it comes and goes. I am going to take it in next week and leave it so they can mess with it. Any suggestions? One more thing is that it doesnt seem to have a lot of power but I was told it has always been that way because of the way it is geared. Thanks

my 95 4.0l has done the hi rev thing off and on for about 5years now, and nobody i bring it to can explain it. the temp guage in my truck hardly ever moves above cold (damn ford and there guages) but it makes excellent heat :licka: