Hi everyone. I purchased a 1993 F150 XLT Supercab 2WD about a month ago, it has the 5.0L, E4OD, and 3.55 gears. When I bought the truck it had been sitting for a while (3-6 months) and the truck has 302,500 kilometers (approx 190K miles). When I got it home I replaced the rear spring hangers/shackles (rusted completely off), cap, rotor, wires, plugs, pcv, air filter, seafoamed the engine (vacuum and gas tank, not in crankcase) and did an oil change.

All this seemed to help quite a bit but it still had a slightly rough idle and wouldn't properly high idle when cold so I removed the IAC and gave it a thorough cleaning. The IAC was very black with a lot of carbon in it but after I was done it was clean and the rod was moving freely. I put the IAC back on the truck and started it up, the high idle when cold works properly now and kicks down after about 30-60 seconds. Now I did read that I should of disconnected the battery for a while so the computer could re-learn the idle/clean IAC, I did not disconnect the battery. Now that the back story is done I will get to the possible issue(s).

I took the truck for a drive tonight (in town) and this is kind of hard to explain but I will try. The truck seems really sluggish/slow to get going when starting out almost as if something is holding it back and then releases it and it goes fine. Could this be a symptom of the truck trying to re-learn due to the IAC being cleaned? Should I unhook the battery and then start driving it again? I have only been using it around town but next week I will be taking it to work which is about a 140 kilometers round trip.

The other thing I am experiencing is the tranny shifts very firmly (not harsh, just firm). It doesn't miss any shifts and goes through all the gears fine. Is this normal? The tranny was low on fluid so I topped it up. The fluid that did show on the dipstick was still bright red and did not smell burnt. I will be having a filter change/tranny flush done when I get some cash.

Sorry this is so long I was just trying to be as detailed as possible in the hopes that you guys might be able to give me some answers. The biggest problem is not knowing the history of the truck. For all I know it has a rebuilt engine and a shift kit in the tranny, I just don't know. It does drive pretty nice once it gets going. Thanks in advance for any advice you guys can offer

 

No, that does not sound like the computer is trying to "relearn" the IAC characteristics.

I had a similar problem on my old 1992 F-350. I had it for a~2 years when the same type thing started to regularly happen. Turns out a previous owner installed a set of rear brake shoes wrong. In effect the brakes were self-adjusting themselves too tight every time you used them when moving forward. Once I got the drums off I found one set of new brake shoes on one side, installed wrong, and on the other side a rusty set of original looking shoes and hardware.

Need less to say I was shocked.

 

Does this sluggishness seem to be more pronounced with 1/4 throttle or kind of taking it easy on the gas driving but in the higher rpms, like just before it shifts, it feels really strong? That's what mine does. Mine also seems to be "flooding" for a while if I do some "fun" driving (like really getting on the throttle). And it needs to be " cleared out" by revving it a few times.

I ask this because if so, it may give some more clues.

And you'll be asked about codes as well, got any?

 

The ad on craigslist did say that it had all new brakes, I will have to pull the rears and take a look, thanks for your suggestion.

 

Yes it is definatley more pronounced at light throttle, especially when taking off from a stop. Its like something is holding it back and then when you hit the right throttle position/RPM it is "released" and goes fine, hope that makes sense. I haven't checked for codes because the check engine light isn't on. Could it still have codes stored without an engine light?

 

Yes... yes it can, so pull the codes and while you're at it check fuel pressure, if it's less than 32psi at idle then you have a fuel delivery problem... which wouldn't be that surprising from a vehicle that has been sitting.

 

Thanks, I will try and check the codes tonight or sometime over the weekend and see if that points me to anything specific. If it doesn't I will check the fuel pressure.

 

If mine, I would also disconnect the negative post of the battery for a few seconds.

 

I am going to check for any stored codes first and then once I have that information I am going to disconnect the battery for a while to clear them out (if any). I haven't driven the truck a lot but this weekend and upcoming week I will be putting a few hundered kilometers on it so the computer will have a good chance to re-learn everything.

 

Yours sounds so much like mine, my fuel pressure was perfect btw. I'm just getting to get this issue figured out after a year of doing other stuff/projects so that's why I'm paying attention!

Ps, I have no codes either. I had been told (and haven't yet) to look for vacuum leaks. I do know that my AC will come and go with different amts of throttle and that is prob a vacuum leak as well so there may be something to looking into that for this issue as well.

 

Ok so I can get a cheapy fuel pressure gauge at work that I can mount on the fuel rail so I am going to grab that. What should my pressure be at idle/when revved up?

 

I just read another thread on another auto repair site that a guy with very similar truck describes exact same issues and replaced EVERYTHING to no avail but he said his AC did the very same thing as mine does where it switches to defrost under low throttle.

Edit: that thread shows the guy replaced his o2 sensor and viola, fixed it!

 

As Conanski stated above, 32 at idle.

 

Thanks everyone, per your suggestions I will take some time this weekend and see if I can get it figured out

 

I put money on the 02 sensor.. my 93 would idle a little rough and have a sluggish throttle response until i threw a new sensor in..