I've been having a lot of issues with my 91 351w. It has a new map sensor, idle air sensor, throttle position sensor, egr valve, vacuum lines, plugs, fuel filter, fuel pressure regulator, and still idles rough. Also it will buck down the road on occasion. I'm gonna try a pcv valve next. Everyone I talk to is stumped over it. It throws a light sparatically as well. Any ideas?

 

Check for codes. The PCM (computer) is trying to tell you something.

 

Where can I go to pull codes? Do dealerships still do obd 1? I'm not very good with counting the blinks lol

 

Invest in one of these:

 

So this will literally give me an actual code that all I have to do is look up? If so it's a life saver for around $30

 

Yes, it displays the codes for you:


And it comes with a book of code definitions. We can help you with that as well.

Some parts stores used to read OBD-I codes for free, but I think that is getting tougher to find. As far as a dealer, they may be able to but I would bet they may charge you for it or insist they get to fix the issue. Only a guess on my part.

Reading codes from flashes is not as bad as it may seem. It is the cheapest method going and the most reliable. Some folks report problems retrieving the codes using a reader. Most of the time it ends up being caused by corroded pins on the diagnostic data port. Easily resolved, but just a forewarning of what could happen.

 

Well I'm going to buy one of these. It seems like a good 30$ to spend and could save a lot of headache. Plus I know a lot of people that I could help with it. I'm ok with the risk of it not being right.

 

I bought one of those code readers and it does come with a Code book also. The best Money I have spent on my 93F150

 

This is just a curious question. But how specific are the codes? Do they just give you a general issue or zero in on what could be faulty

 

Each code has a definition assigned to it, but the exact definition can (and usually does) change depending on when they were displayed (Key On Engine Off, Continuous Memory, Key On Engine Running).

As far as how accurate they are is also dependent on the root cause. The displayed Code is the result of an improper input to the PCM. This code is what the PCM THINKS is the issue. It's a great start to narrow down the problem and root cause, but it is not intuitive enough to know whether the flagged code is a bad sensor or open wire or ??

 

You said new plugs and wire, what about the cap, rotor, PIP sensor, TFI module, and coil. Those will also effect your idle.

 

I haven't done those yet. I've been planning to do it though

 

Did you do the wires? I saw plugs in the OP but not wires. The wires are the biggest cause of problems when they age.

 

I didn't only because. They looked to be fairly new when I bought the truck. But that was months ago. The whole truck needs a tune up bad

 

Well I got some codes pulled. Very vague though as to what the problem may be. I got 22o 23o 21o 24o. They all described parts that I've replaced being "out of range"