(I could use your help) Rough idle...

Discussion in 'General Discussion' started by DeanMk, Sep 4, 2019.

  1. DeanMk

    DeanMk Member

    ...is not a new Canadian rock band, but rather how my truck decided it was going to run today.

    So here's my issue....

    I have a 1998 Ford Ranger XL with 2.5L 4-cylinder and 5-speed Manual transmission (see my avatar).
    Truck starts ok, but idles very rough.
    Most times, does not run more than a few revolutions before dying.
    Tried putting my foot into the gas, engine is slow to react. Sometimes rpm's come up slowly, sometimes revs up quickly, but in spurts, then dies, then revs up again (gas pedal floored the whole time).

    It's like someone disconnected the high idle circuit and its trying to run on low idle upon initial start up.
    However, the lagging engine response (when the I move the pedal) has me thinking there could be a bad sensor somewhere.
    ….but where?

    I have no computer diagnostic tools, so its not like I've got an E.D. machine just sitting in the garage.
    The last time I tried to start it, I got it to run (after several starts) just long enough so that I could run out of the cab and I was able to tap on the whole intake, from the air cleaner, back (thinking one of the sensors might be dirty and maybe just a good smack would clean it enough to get the engine to run again).
    When I smacked the metal shroud that covers the throttle controls, the engine suddenly revved up, like I'd smacked it into high idle, then it immediately died.
    I see no broken wires or connectors.
    Battery is in good shape.

    What do you think is wrong?

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  3. OP

    DeanMk Member


    So, I decided to continue researching my plight, because honestly, I had NO idea what to look at, or for, with this thing.
    I started to notice a number of posts pointing to issues with the Idle Bypass Valve (some of you call this the IAC).
    It seems they sometimes get some crap stuck in them and this causes idle issues not too different from what I was experiencing.
    So, I took a look through Goggle Images to see what it was I was looking for, then went out to the truck (with a little carb cleaner in hand) to see if I could find this thing (it seems all Ford engines use the same IAC, or at least it looks the same, because all the pics I found showed the same unit, despite what engine it was connected to).
    I found it!
    Bolts onto the BACK of the intake manifold, behind the metal shroud I smacked in the other post, making it a real PITA to get off (the two bolts that hold it on look back towards the firewall :mad:).

    ….then it hit me....

    The reason for the problem is crap stuck in the IAC (or at least the passage it works with), so maybe I don't have to disconnect anything!
    Quick search of the ol' round house turned up a stick and while it was (attempting) to run, I gave it a couple of smacks with the stick, right where it bolts to the manifold.
    Dam'd if it didn't, the engine sprang to life and started idling like it was supposed to!
    I almost cheered!
    However, while the idle smoothed out, the engine kept almost dying then coming back to life. so every time it started to die, I'd give it a couple of smacks and it would run again.
    Eventually, though, it died again.
    When I went to start it, I tried the old flooring the gas again and I think that helped, too.
    Dying engine frequency decreased and after a while, it actually idled smoothly all on its own.
    I felt comfortable enough to take the garbage up to the highway (it's garbage day), then took it out on the highway for a little test drive.
    It did stall out when I came to a light, but started right back up again and idled without having to floor the gas or smack anything.
    When I got home, I pulled the top off the air cleaner box and shot a couple of spurts of carb cleaner up into the engine to see if that would help.
    Not sure if it did, but it was running fine when I shut it down.
    After all the BS I've been through today, I feel REALLY lucky on this one.

    Last edited: Sep 4, 2019
  4. OP

    DeanMk Member

    ...well, maybe not so much of a fix...
  5. OP

    DeanMk Member

    After I made my second post and took care of a few other things around the house, I decided to take the truck out for a longer test drive just to make sure my "fix" actually took.
    This was about an hour and a half after I last messed with the truck.
    Problems seemed to be back, but not as bad as before and a bit of a drive (about 20-30 minutes) had it running smoother, but you could still tell something was amiss.
    It wanted to buck and not always respond correctly to the gas pedal (i.e., flooring the gas did nothing, then the engine would rev up suddenly).
    After some thought, I figured maybe I'd just go ahead and replace it.
    Next morning I picked up a new IAC and replaced the old one.
    While I had the IAC out, I shot some TBI cleaner into the hole, as it seemed pretty dirty.
    I didn't get too heavy handed with cleaning (the hole is on the back side of the manifold and there's not a lot of room between it and the firewall). A few shots with some TBI cleaner.
    Doesn't look like I did much, but at least I made an attempt.
    ANYWAY...the idle smoothed out...
    Now it just doesn't want to go anywhere!
    Response to the gas pedal is now erractic and violent!
    I drove about 2 miles down the road and it was all I could do to get home!
    Wondering now if I have multiple problems, or maybe it wasn't the IAC at all (or maybe I bought a bad one?).
    What else could be going on here? TPS? I'll probably test that next.
    If anyone has any ideas, please chime in.
  6. Tom Autry

    Tom Autry New Member

    This problem seems serious enough to store a code in the computer which should lead you in the right direction. You can purchase a decent code analyzer for around 50.00. I wouldn't suggest to invest in an expensive reader for the average consumer. One of these should do the job.
  7. OP

    DeanMk Member

    One of what? Did you mean to leave a link?
    Can you recommend a specific reader?
  8. Tom Autry

    Tom Autry New Member

    Sorry... it is a code reader. A device you plug into the diagnostic port located under the dash by the steering column . It will read your computer and give you the failure codes that are stored there. You can get one on E-Bay fairly cheaply. The more expensive ones, the more info they will reveal.
    Last edited: Sep 9, 2019
    DeanMk likes this.
  9. OP

    DeanMk Member

    Ok. Thanks Tom.

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