1995 flareside extended cab 6.5 foot long bed 5.0 automatic. When I first start the truck in the morning it will idle normally for about a minute or so then it will it pulses revving up and down constantly and after 5 to 10 min it will quit and idle normally. Even after the truck is warmed up if I rev the truck at all it goes right back to pulsing. I was told changing the coil would help since every time it pulses the battery gage goes down with the low revs. Idk what it is maybe a vacuum line but not for sure, please help. Thanks.

 

A few things come to mind - possibly a bad/dirty idle air control valve, possibly a bad alternator (might explain why you are seeing the battery gauge dropping at the lower rpms - the alternator just can't handle the load of running the truck at low idle), possibly a bad throttle position sensor, possibly a vacuum leak.

Lots of possibly's. I'd look at the IAC and the TPS first. Search for threads on how to clean/test them - lots of good info.

 

I didn't think about the alternator before, I got subs in my truck pushing about 1100 watts and I can watch the battery gage drop when the bass hits so I could of screwed up the alternator with that, I'll check the other things you suggested and thanks for the help

 

if you can se the charging system being abused that hard then you need to swap to a higher output alternator regardless. the 3g swaps are pretty easy