jdaum1222

Hey everybody looking for some advice/help/etc:

My '91 F-150 i6 300 has started idling incredibly rough to the point that the whole truck feels like it's shaking. The tail pipe bounces up and down while parked and the exhaust note has changed pretty drastically (which I wouldn't necessarily mind if I intended for it to. It sounds almost like a V8 with a nice bassy lope).

As soon as I start driving over about 10 mph, the shake goes away and at 45 mph, the truck is only pulling 1k rpm with no shake. My fuel economy has dropped from about 14 - 15 mpg to anywhere from 8.5 to 10, but I haven't noticed any significant loss in power. The truck only has 13X,XXX miles on it and has been maintained beautifully. All of my gauges read normal and the truck runs great otherwise.

Any advice, recommendations, thoughts, crystal ball readings would be greatly appreciated.

wde3477

Suggest the first thing to do is pull the codes - it's cheap, and at least it helps eliminate what it's not.

If it were just a rough idle, would suggest to check / clean the idle air control (IAC) solenoid. Your drop in mileage raises questions of whether your fuel quality has changed, or something that hopefully the codes will bring to light is going on. Way-out-there things could include a weakening coil and related spark.

Good luck, and keep us posted.

Chris_1

iTrader: (1)

Vacuum leak ? But pull the codes as suggested - it's not just cheap, it's free. And will probably save you a bunch of money by not playing try this.

jdaum1222

Update: dropped a valve in cylinder two. Any recommendations on good crate swaps?!?