Hey guys got a quag that I would appreciate some help on..Its a 93 F150 5.8. The problem im having is its fires right up but within a few second the idle starts to jump around and unless i feather the gas and or keep my foot on the accelerator pedal she will die . Here is what ive done so far: even though I had no codes for it I changed out the TPS. While I had the throttle body off I cleaned the throttle body out entirely which was pretty dirty. I also removed the IAC and cleaned that out as well. I also checked for proper IAC plunger movement and I beleive the plunger was moving correctly (full open to fully closed). I also checked for vaccum leaks with brake cleaner and wasnt able to find any. After i did all that and put it back together it stil does the same damn thing, so now im searching for someone out there who has had similar issues....PLease help me out guys.....Thanks!!!


Note : Air filter is clean

Mark

 

Any stored EEC trouble codes?

 

Map sensor?

 

no codes to speak of......

 

not too sure it would be the map sensor seems how i dont have any codes for it

 

still looking for some insight guys......any help would be appreciated

 

How does it run when going down the road? Does it want to stall at a steady speed? Does it accelerate ok? Have you checked fuel pressure at the rail? Will it do it on both tanks? I don't beleive the map will throw a code unless its completely out of range (bad) but you said the TB was really dirty, im sure if it was bad the rest of the intake could be bad as well. Which is where the map plugs into. It may not be the map and maybe a fuel delivery problem. It could be that the Iac is inoperable as a whole. This about all I can think of without a little more info on what it does in other situations. Sorry for all the questions but I would really like to help.

 

Never change a part unless it fails a published test. And any time you change a part, test the new one before or during installation.



The only exception to that rule is the MAP - it won't necessarily throw a code, and testing it isn't easy. Just snag a few from the JY and swap them in. If one of them makes a noticeable improvement, buy a new one. If not, hold onto the spares for later.

Cleaning the TB isn't advised - it works fine with the buildup. It's called "sludge-tolerant", and cleaning it removes the sludge-tolerant coating.

Cleaning the IAC is risky, and in my experience, only for diagnosis. They don't seem to last after cleaning, even if you follow the procedure in this caption:



But before buying or changing any more parts, test fuel pressure, valve timing, ignition timing, & the ignition system according to the procedure in Haynes Ch.5 (usually Sec.5 or 7).

. .

 

thank you very much for the responses guys, as it turns out it was indeed the MAP sensor..My brother was kind enough to allow me to use the one off his old ford as a tester to see if it made any noticable difference and it did... once i installed the new part everything was perfect....thank you guys so much for the help you gave me...

 

Glad it worked out for you!