I've got an '89 f-150 4x4 w/ 4.9L I-6. Doesn't seem to idle quite right. At start it'll idle at 1500 or so for a couple of minutes before dropping down to about 1000. It'll finally get down to 600 rpm's after it's good & warm. Is this normal? Also, seems slow & sluggish off the line but suspect it's in my gearing. Truck was originally set up w/ 235's now running 31x10.5's If I'm running around 2000 rpm's at 60 mph can ya'll lead me in the right direction on gear ratio?

 

if its a cold start then that is normal. if the idle would drop off fast to an almost stall then i would suspenct the IAC. u can always clean the IAC and its passages out if u like but it probaly wont help much. also, is the check engine light on at all?

as for gearing, check ur rear axle ID tag. should be bolted to the diff cover. let us know what gears u have so we can go from there.

 

Your axle ratio is on the door post ( B post) on the vehicle sticker. It is a code letter and if you post it someone will tell you what the ratio is.It is almost easier to block wheels, put tranny in neutral, jack up 1 rear wheel and rotate wheel slowly counting the driveshaft rotations and divide by 2 (ie if wheel spins once and driveshaft goes round 7 times you have 3.55 gears)

 

I guess I'm dense....why do we divide by two?

 

umm ya look on the rear axle for a little metal tag like i said...it should read something like "3 55"...