My ford ranger '96 6 cycl. is reving up then settles down over and over. If I'm sitting there with my foot on the brake it will click then rev about 3000 rpms then settle back down, then do it again, about every 10-15 seconds. There is also a background with this problem: This truck, ever since I bought it revs high at start up.. at least high in my opinion. I have to wait about 10 seconds till it revs down to where I can put it in gear. I'm putting my truck in gear at 15k rpms and I think the normal 'high' rev is about 10,000. Right now it's idling at about 6-7,000 rpms, clicking, revs up 3,000 rpms then back down. Now I had this problem before and they ended up fixing it but charged me lot and when I got the truck back, it still reved high at start up but the clicking was gone. I think they did an Injector flush but also some other things.. they basically sold me the farm. Unfortunately my mechanic report is in the hands of my accountant as that happened in Dec.