I have this truck my dad bought for $1000, the previous owner had re-done the entire fuel system and replaced a good amount of parts. The problem with it is when I start it it will go between 2800 rpm's and 800 rpm's for about 30 seconds and then die, if I give light gas maybe 1 inch pressed on the pedal it will keep it alive a little longer but it shakes the entire engine and creates white smoke out the back, if I press the gas to hard it does nothing, after about 30 seconds it dies. I have replaced a good amount of stuff on here and surfed youtube, these forums, reddit, quora, basically everything you can think of and have tried so many fixes but I just cannot find the problem and its really annoying me, does anyone have any ideas? I have been making a list this entire project of things that have been done and things that might fix it, I will attach it if that helps, I am new to working on cars and these forums so please treat me like a 12 year old when explaining things to me, Thanks! :]

 

Welcome to the site!

Would be helpful to have the basic truck details, such as engine (4.9L (300), 5.0L(302), 5.8L(351)), transmission (auto/manual), model year, trim level (XL, XLT, etc.), miles, any aftermarket parts installed, time since the last major maintenance for plugs, cap, rotor or other engine work, etc.

Offhand, your idle surge sounds typical of the idle-air control (IAC) solenoid, usually clogged with crud and the internals can be cleaned with carb cleaner, but failures are getting more common as they age. Not to overlook the problem could be from other causes as well.

With all the things listed as 'checked' - what were the results or findings? For all the parts replaced, what brand(s) were used?

Suggest to pull the engine codes - there is a Sticky note at the top of the forum describing how to do it yourself - hoping the computer has flagged something to narrow the possibilities and to reduce troubleshooting efforts.

 

Sorry forgot the truck details somehow, its a 1989 ford f150 xlt lariat 302 5.0 manual, 80k miles, part list included (a lot of them were installed by the previous owner in the past 3 years so I don't know the brand. I completely cleaned the IAC and throttle body with carb cleaner, and with everything else on the list I have done I have noticed no change, still does the same thing. I pulled the engine codes with an obd1 tester and only got code 11, from my understanding that means all ok on key on engine off test, I tried to do a key on engine on test but it wont run long enough for it and its just to unstable. Thanks for reply!

 

Check to see if someone messed with the idle hard stop screw on the throttle body. It shouldn't be adjusted where it is holding the throttle plates open at all.

 

I checked it and it seems fine, https://photos.app.goo.gl/4RZYiTzvtuHAsGVz5 there's a video of it.

 

Maybe just my interpretation with the lighting, but it seemed like the butterfly tab wasn't being pulled securely against its stop, as if either there was crud preventing free movement or the return spring may be weak...????

Suggest another thing to inspect - rock the butterfly mechanism side-to-side for any free play. Had an interesting occurrence on another vehicle where it seemed the butterfly shaft had worn / wallered the casing, allowing a bit of excess air in through that way. Haven't heard of this being a problem with this model line, but another thing to cross off the list of things it ain't.

 

I think its on pretty secure, I have attached some more videos to this link https://photos.app.goo.gl/UCKfHxnRtwn3y9Fj6 and in one of them I hear a weird noise like a vacuum leak, does it sound like anything bad to you? I also found this weird thing in the top left of the truck that the wire/hose is not attached to, what is this and could it cause this big of a problem? Thanks :]

 

Easy one first - the vacuum line and actuator you have circled is for the Max A/C recirc damper. Yes, it should be connected, but shouldn't have vacuum on it unless in Max A/C mode, in short, don't believe to be a part of your bigger issue.

Your video on the butterfly does suggest that it's not being pulled tight against the stop, figure that's a higher priority thing to look at towards having it freely move and securely rest on the stop every time.

Couldn't really tell with the video on the vacuum noise, other than it shouldn't sound like that.

If you can keep the engine running long enough and stable, such as a friend's foot on the pedal or the bevel of a larger screwdriver slid into the butterfly tab / throttle stop gap to an appropriate point - would be easier to chase and locate such as with a piece of larger tubing, one end stuck in your ear and the other end moved around the engine bay to localize the source. Another alternative requiring a good bit of caution is to lightly spritz carb cleaner around the manifold gasket areas and such, listening for whether the engine speed changes.

Had a past event where a section of gasket failed between the upper and lower manifolds - could hear it but took a combination of the above tricks to locate it directly behind the distributor.

 

Alright Ill add the actuator and vacuum line for things to fix after its running.

I'm gonna go up there later today and look at the butterfly stop and see what I can do, (push it against it while its started to see what happens and adjust a few thing to make it stay against it) would you think it not resting against the stop could cause these issues? I know the previous owner replaced the entire thing.

I am very suspicious of a vacuum leak but the engine is definitely not gonna run long enough or smooth enough for me to listen for it, I blew cigar smoke into a few hoses for about 30 mins and didn't see any smoke coming out of anywhere besides a tiny bit in the egr valve, I might just go out and see if an auto store will let me rent a smoke machine.

 

It's my understanding that the Stop is set only to prevent the butterfly plate from becoming wedged in the throat or to prevent wear over time due to any repeated contacts between the plate and the throat.

Consider that if the butterfly plate does not return to the same position every time, the idle-air control (IAC) valve will move to a different position each time within its range towards achieving the target idle speed. This could be made worse if the butterfly shifts a bit when it should be in a fixed position resting on the stop. Any crud or movement restrictions with the IAC just adds another degree of difficulty to the troubleshooting.

Suggest to get the butterfly moving freely and closing reliably, then see where you're at with this challenge.

Will admit that a small vacuum leak could also present the issues you're seeing, but until you can get it running long enough to go down that path, kinda stuck there.

Going on the thought that if you don't know what the problem is, start working through what's not the way it should be. - a process of elimination approach.