a1badboy

Hi guys, I'm new to your forum,did the search no luck. 94 v6 extracab 4x4 automatic 155000 miles, when its cold and on the high idle circuitit has a very pronounced miss,as soon as it goes to regular idle it runs smooth as silk. I had a complete tuneup done about 4000 miles ago, where should I start? Thanks
edit:It seems to be #1 cyl pulled plug it looks fine but put new one in same problem as soone as it's warm enough to come off hi idle it smoothes right out????Edit: Well found out it was a bad headgasket, has any ever used the steelseal product? pros or cons? thanks