Just like the title states..

I have picked up this total beater truck 1989 F-150 302 engine...

Truck runs.. drives...


But likes to randomly stall while sitting in Drive. if I just let the truck idle it will sit there and idle all day long without any hickups..

only strange thing to me is it does the pulsing idle when first starting the truck. but tap the gas and it is gone.

looks like the tps,coil,wires, dizzy cap and rotor have been replaced also the map looks a lot newer then the truck.

I replaced the IACV with another newer one.. same random problems..

also when the truck is driving it feels like it is falling on it self. but if you mash the gas she wakes up and hauls..

Still has the smog pump on it.. even though I know the cats are long gone.. maybe some other emission crap??

Also the check engine light is on.. But how does one check the CEL on something this old??

Sorry.. I am kinda new to Fords.. even tho I will commend this truck on taking a ass beating and still kicking.. .

 

EEC-IV code reader from Auto Xray, us mustang guys still use them as that is our OBD equivalent. I would check to see if there is any water in the MAP sensor and make sure you have good vacuum and check the hoses. You could have a vacuum leak somewhere.

 

I mean us FOX mustang guys still use EEC-IV.

 

MAP sensor is a common problem with the Speed Density engines like this one. I would check there first. If that checks out, check the fuel pressure. Does this truck have dual tanks?


You know what I do with every older Ford I own? Unplug the IAC and find the idle screw that they say not to tamper with,then get the vehicle to idle on it's own.. Solves every stalling problem that can be mustered up

 

Lol yes the truck has dual tanks.. front one is the one I use rear is full of rust and never had a gas cap on it when I got it.

Going to check the map sensor out tomorrow.. stupid rain stopping me from doing anything.. also I would not be shocked if it has a vac leak somewhere there is way to much vac lines running around on this motor for my taste.

thanks for the tips so far. will check back in when I find something out

 

check vacuum line going to MAP sensor

 

Ok finally got around to checking the Codes..

truck threw out..

#22 MAP/BP sensor out of self test range.


#34 PFE or EVP circuit above the closed limit of 0.67 volts.


#67 Neutral Safety circuit failure


So I replaced the Map sensor... yay.. another 40.00 thrown into this turd..

anyways truck runs a lot better is not falling on its face while driving and no more Cel at the moment..


Now another problem has arrived and is pissing me off... truck has a nasty surging idle after it warms up.. like If I am in drive the truck is trying to lunge forward and almost stalls and repeats..

also the truck is idling quite low.. right around 500 rpms.. it never did that before..

I was thinking Idle air valve. But I have replaced it twice with known good ones and it still does it. also its strange cause the truck will stall once in a while when this surge is happening but restarts right away and idles fine till the next stop light.. its really annoying cause I am trying to cruise through a parking lot and its lunging forward over and over.

 

Base idle needs to be adjusted I bet. If the truck won't idle on it's own with the IAC unplugged then you have to adjust the throttle stop until it does. There's a few steps to adjusting the base idle that a quick google search will show you

 

^ hmmm.. trying to locate said idle adjust.. I cannot seem to find a thread on it online anywhere they are saying its controlled by the PCM..

I am going to go out there and tinker with it in a minute to see if I can figure something out.

 

Everyone always said the PCM controls it, but there is still a base idle that needs to be there regardless. When engines age the base idle usually drops, so there is always an adjustable set screw, but sometimes they are frozen and you can't move them.

1. warm it up to operating temp.
2. Shut the engine off and un-plug the IAC.
3. Start it. If it doesn't start, turn the idle screw, below the throttle cable, on the throttle body, untill it does. Once it is running with the IAC still un-plugged, adjust the screw untill it idles at about 650RPMS.
4. Shut it off and reconnect the IAC.