I have a 1990 bronco with the 351w truck has about 135,000 miles and that goes up everyday. At start up the truck will sputter and almost die then the RPM's will kick up to 1200 and it will warm up as usual. Sometimes almost rarely at stop the truck will hesitate off idle and one time it died on me. I was able to get it restarted and it drove fine the rest of the night. It uses oil(can smell it very rarely in cab) leaks it I believe too. I don't smell burning oil from the exhaust. Exhaust did have leak repaired and was checked for more and came back leak free. I'm about to have the PCV valve replaced, along with plugs, wires, and all the filters. Here's my question. This truck is my livlihood right now. I deliver pizzas in it. Am I screwed? Am I 5 or 10 thousand miles away from the motor puking and me losing my job? Need any advise to help me here because this really scares me.

 

Personally... I would do an inspection with a mirror.... see where the grunge is building up....

First pull a spark plug and see what they look like.... are the oily or just dirty and used up.... 135k miles is a lot for plugs.....

Also you have efi... and before I would replaceing stuff I would sea-foam the throttle body out really well to get things as clean as possible..... and see what that does for you....
And dont forget about the air filter.... I would check that asap and see what that looks like.... I never run the paper POS ones because they are about half a K+N which will last forever... usually 100k on the street without cleaning.... and I run them....
It that wakens the Bronco up a little you are in the clear...

So lets say you do plugs, seafoam and air fliter and get back to running nice then onto vc gaskets

I would think you have bad valve cover gaskets that need to be replaced.... they ususally die in ten years no matter whose you use... if there are leaking... remember use an inspection mirror to look this over... you want to replace them too... and not with the elcheapo cork junk either... Use metal core nitrile rubber gaskets and install them... start tightening in the middle of the vc and work out.... then run through the bolts a few times to tighten them down... not farmer tight either... a little past snug works just fine... You might want to invest in ARP studs too because they make doing it way easier. If you go with studs you can hold the gasket way easier before you put the cover on it... just use a little blue loctite on the bottom of the stud...

That may get you from 135 k to over to 200 mark....

 

Replace the spark plugs, wires, rotor and distributor cap. I sounds like you may have a sensor going bad too. May be the throttle position sensor (bottom of the throttle body, works off the throttle shaft) The oil leaks ? How much oil do you have to add between oil changes ? How often do you change oil ? I don't think it's going to take a dump anytime soon, just sounds like it needs some TLC.

 

You deliver pizzas in a V8 truck? How do you make any money?

In any event the stumbling off idle is likely because of a vacuum leak, the common things that cause this are the "juice can" vacuum resovoir on the passenger side inside fender.. it rusts out on the bottom so I suggest you visit a junkyard and snag a plastic resovoir to replace it with. Another possibility are cracked or broken vacuum lines, for the most part they run from the solenoids near the coil around the back of the motor to valves in the smog system at various points, so just make sure they're all connected for now. Replace the juice can first and see if that cures your problem, if not then you'll have to look at the vacuum lines a little closer.
I'd also suggest you pull the codes to see if the computer has anything flagged, this can be done without any special tools by following the procedure here.. Fuel Injection Technical Library » How To Run a Self-Test, but an Equus 3145 code reader will take all the guess work out of it and they're not expensive.. Equus 3145 - Equus OBD I Code Readers - Overview - SummitRacing.com

I wouldn't worry about your engine dying anytime soon either, with regular maintenance these things often go 200-300k miles.

 

Replaced coil, pcv valve, cap, plugs and wires. Vaccuum system was check and found no leaks. Still occasionally wants to stumble and die off idle. What do I have to do to get this to run right?

 

Start with the throttle position sensor.

 

Everything is off, removed TPS, ran out of light, will finish tommorow. Couple ?'s. What is the propper orientation of the sensor?(pics welcome) Also how do I know if the tangs on it are engaged properly?

 

If I remember correctly, it only goes on one way. Only changed one, that on my 95 E150 van with a 351. I don't recall exactly how it was acting up, but after changing the MAP sensor and one other, the TPS turned out to be the culprit.

 

new tps and everything is back on. still acting up. What else could it possibly be?
You guys have no idea how much I want to put a bullet in the engine block.

 

Have you tried to hook up a code reader and see if it's throwing any codes ?