ilovefords31

I really hope someone can help with my 1986 ford f150. It has a 4.9 300 ci engine, and a c6 transmission. I am having an issue with cold startups. When I first start the truck after sitting a few hours, or overnight it rough idles and the cold idle is very low, and it tries to stall when I put it into gear. If I give it a little gas it won't stall but it is very difficult because I am parallel parked. This has the Feedback carb system and I have changed pretty much everything except the IAC, Mixture control solenoid, and the smog (air pump) and components. Changed the transmission filter, and fluid about a year ago, and this all just started about 4 months ago right after using seafoam poured into the carb throat, and fuel bowl vent. Does anyone know how to test the IAC on this system?

Matthew Burr

I have the exact same engine (mines manual trans tho) and although someone long before me tore off all the smog equip, i dont believe it has an IAC, thats part of a fuel injection set up, which the v8's of the same year had.

you might have knocked some gunk loose into the carb with the seafoam. try unscrewing the idle mix screw and blow some compressed air through it (not the canned kind, but regular air compressor kind). gently screw it all the way back in and then back out 1 and 1/2 turns.

you can test the control solenoid with a 9v battery, if you hear a click it's working.

on the passenger side under the hood there is a MAF sensor, if you havent replaced it you can try cleaning it with carb or break cleaner spray

ilovefords31

Idle Air Control Valve 1986 Ford F-150 4.9 ltr 300 CI Engine With Feedback Carburetor System


Mathew thanks for the reply. I am confused. I looked the part up on rockauto and it shows it as an Idle Air Control. Where is the MAF sensor? I'm talking about the little motor that is supposed to raise the idle if the engine is trying to die. It does not do that anymore. It just stalls. It used to raise the idle for me. After I get it into gear it stalls and then I restart it, and it doesn't stall, just rough. One thing I should mention is when pouring the seafoam, it makes the engine stumble really bad. So, I was thinking along the lines of maybe it burned out the motor to the, what I thought was, the Idle Air Control. If that is not what it is, then please let me know, so I don't order the wrong part.
Here's a pic from rock auto. It looks pretty similar to whats mounted on the carb.

Matthew Burr

lol oh, thats a solenoid, hardly a valve

it's intention is to keep the engine from dying when you suddenly pull your foot off the gas. really only necessary if you have AC on your engine. mine malfunctioned, i ganked it and havent ever had a problem with it.

you should be able to hook it up to 12v and see if it extends, if it doesnt then it could be malfunctioning

Matthew Burr

sorry, not MAF, MAP, it should be attached to the passenger side fender wall with some wires and vacuum going to it

ilovefords31

Great, I will try them both in the morning. I appreciate your time. I am so tired of not knowing what is making it run so rough. The garages around my area won't work on older vehicles like this, so I am having one hell of a time with this. If it was just plain carb then I would have no problem figuring it out, but this feedback system just plain sucks for diagnosing!

ilovefords31

Well... I did all of that, and no change. I also sprayed carb cleaner around the carb, and hoses, to check for leaks and there were none. I checked the throttle motor (IAC thing) and it works. I Adjusted the choke. Nothing. I have no idea what to do next. Do you know what would be the symptoms of a MAP sensor needing to be replaced?

Matthew Burr

map sensor is usually erratic idle. if you unplug it and it performs better than you know it's malfunctioning

you are setting the fast idle by depressing the gas pedal fully once before you start it right?

ilovefords31

Yeah I always set it, but I haven't tried disconnecting the map sensor. I sprayed it out with MAF cleaner, but there was no difference. I am starting to lean towards the carb is not adjusted correctly. Like the IAC stop screw. I left it the way it was from the factory. I don't know if they adjust them. If they do they must adjust it on the engine they have which s different from mine I'm sure. I don't have a tachometer though so I have no idea how I'm going to set it.

ilovefords31

Well, I adjusted the idle stop for the IAC about 3/4 of a turn and now it is idling great, and no more stalling when I put it into gear. It looks like I had to adjust the new carb to my engine. Thanks greatly to all who helped, and god bless!