My 89 f150 with a 300 6 has developed a little problem. When the truck is cold and you start it up the high idle is great and smooth, however when it drops to the low idle it has a bad throb. Any suggestions? Thanks

 

it could be a lot of different things. whats a bad throb? like a miss or does it die?

 

THROB??
Do you mean it is surging??

Sounds like a vacuum leak...

ftwfred

 

my 66 does the same thing after I intalled a 2 barrell on it, I tuned it a bit rich and after a while of idleing it surges real bad. I just figured that it was loading up on fuel. when I goose it it smooths out. the cold weather could be doing somewhat of the same thing to yours. at least thats kinda what im figuring out with these inlines. just my 2 cents

 

Well i suggested to advance the timing but he said the surging isnt as bad as bumping the timing. Could it be a sensor by any chance?