problem with 98 F-150

375H&H

Truck had 136K on it when the top end let go (5.4L). Had a brand new crate motor put in , same motor 5.4L . Motor runs good , I think I have around 6 or 7 K on it . Now for some odd reason it's idling @ around 1200 or 1300 RPM , it did idle @ around 750 RPM . Any reason why the idle would go high on it all of a sudden ?

1200 or 1300 RPM in park , than drops to about 1000 RPM when you put it in Drive . No miss , runs good , but why the increase in the idle all of a sudden ?

Thanks for any & all help

DPHMIN

sounds like a vacuum leak.

Horse Plains Drifter

quote:Originally posted by DPHMIN
sounds like a vacuum leak.
Yep, check all vacuum hoses on/around engine.

1911a1-fan

vacuum leak is the first thing to check, but with that engine the iac is notorious for going bad


has the check engine light came on ?

mogley98

Probably higher RPM

375H&H

No check engine lite . will check vac lines .
Thanks for the info fellas . Greatly appreciated !!!

1911a1-fan

i have replaced the idle air control 2x on my exploder due to low idle, a friend had to replace his on a mustang due to high idle

unplug it and see what happens while your checking for vacuum

wiplash

Check the big vacuum line on the brake booster. I had two Ford trucks that went to a higher idle when they went bad.

merlinn

You can spray some starting fluid in strategic spots and if the engine speeds up, that is where your vacuum leak is. I think you can use wd40 or brake cleaner as well.

jltrent

Choke pull off isn't pulling off.

john w

I would fill it with shell high test and put 2 cans of seafoam in the tank. When idling pull back the throttle arm toword the stop and see if the idle drops. You may have carbon buildup in the throttle body. Get a can of throttle body cleaner and clean the throttle body

john w

I would fill it with shell high test and put 2 cans of seafoam in the tank. When idling pull back the throttle arm toword the stop and see if the idle drops. You may have carbon buildup in the throttle body. Get a can of throttle body cleaner and clean the throttle body

Horse Plains Drifter

quote:Originally posted by jltrent
Choke pull off isn't pulling off.


That's it!!!

montanajoe

quote:Originally posted by DPHMIN
sounds like a vacuum leak.
+another,,

375H&H

Thanks again , very much appreciated .

375H&H

Being told its an intake gasket that's sucking in air [:(] Great , another bill I don't need [B)]