High idle. Engine won't slow down while coasting. No HVAC controls. P1506. Related?

Discussion in 'Engine Tech' started by spenc938, Jul 18, 2012.

  1. spenc938

    spenc938 New Member

    I have a 98 2WD ford ranger with a 2.5L. I bought it a little over a month ago and I noticed shortly after that it was idling a little high. It seems like it's gotten a bit worse and now it idles at about 925-975 RPM. Its not a perfectly smooth idle, but it isn't too rough.

    The motor also doesn't slow down while the clutch is in or while its in neutral until I come to a complete stop. If i'm at 2500 RPM when I take it out of gear, that is pretty much where it stays until the truck stops.

    Also, the HVAC controls don't work. It always blows out the dashboard. Changing the temperature, speeding up, slowing down, going WOT, idling, all have no effect.

    It also has a check engine light, P1506. For about two weeks it was only a pending code, but now the light is on.

    Things I've checked/tried:
    Clean IAC valve, throttle body, and MAF sensor
    Tested the TPS. It reads .8 volts at idle and 4.75ish at WOT. Seems normal to me.
    Unplugged the maf while idling. The truck dipped down to about 600 RPM for a split second, then right back up to 950. No other change
    Unplugged the TPS while idling. No change.
    Unplugged the IAC valve while idling. Truck drops down to about 850.
    Plug it back in, back up to 950. So it seems like it may need to be replaced. I also noticed, that while it was off for cleaning, it appeared to be open slightly. I'm not sure if this is normal.
    Sprayed brake cleaner on a couple vacuum hoses (I doubt I got them all, and my truck doesn't really appear to match what's on the vacuum diagram sticker) and around the throttle body and intake manifold. No change.

    As far as the no HVAC controls go, I looked for the little "orb" that everyone refers to when this topic comes up, and I can not find it.

    I can replace the IAC valve but I wanted to get some input first. Thoughts, tips, tricks, suggestions?

    Edit: About the vacuum orb thing. The truck has larger tires, removed fender well liners, and a swapped motor (from a 99). I'm thinking they could have removed it for any one of these, and never put it back.
  2. maranger

    maranger New Member

    try replacing your iac, usually takes 15 min
  3. spenc938

    spenc938 New Member

    I swear I had read somewhere that they were about $100. Which is why I've been hesitant. But I just checked auto zone and they're only 39. Much more reasonable. And, there is a 24HR auto zone three miles from me. I'll report back in an hour.
  4. spenc938

    spenc938 New Member

    I reset the CEL with my Ultragauge, and then replaced the IAC valve. The check engine light is still off, but I only drove it about four miles after.

    The idle has gone up even higher. Now it sits around 1050. Other than that, no change.
  5. maranger

    maranger New Member

  6. spenc938

    spenc938 New Member

    Well the check engine light came back on, so I swapped the old IAC back in. Hopefully Auto Zone will let me return the one I bought.

    But, I did find something interesting...

    The white one connects to a black one then appears to go up under the dash.

    The black one connects to a red one then goes off with a bunch of other lines.

    Then while taping these out of the way I found this...
    A gray line that appears to go to the same place as the white one that I mentioned first.

    I guess these are the remains of my HVAC controls...? I sprayed brake cleaner on, in and around them with no change in idle. I still haven't found any leaks. I've heard that propane works better so I'm going to look for a hose to put on my torch and try that.
  7. pooleo

    pooleo New Member

    The black line is the vaccum to the HVAC controls. The grey one is I dont know but all my ranger have that grey one with the same cut hanging down by the firewall.
  8. spenc938

    spenc938 New Member

    So, I reset the CEL light and replaced three hoses that were cracked/in bad shape. I replaced the one that goes from the valve cover to the throttle body. And also the two that are connected to this thing...
    Sorry, I'm not sure what it's called.

    It seemed to run a little better, but after about 2.5 days the CEL light is back on.

    What is a good method for checking for vacuum leaks? I've tried both brake cleaner and a propane blowtorch with a hose on it and I haven't been able to find anything. Even putting the propane or brake cleaner directly on the cut HVAC lines doesn't do anything noticeable to the idle. I'm off to the junkyard in the morning to look for a new HVAC orb, but I would still like to be able to check for leaks elsewhere. Also, does the HVAC orb have an actual name? I'm always seen it referred to as the orb or vacuum ball...
  9. pooleo

    pooleo New Member

    what cut HVAC lines are you referring to? If you are checking any line on the truck side, it wont have an effect. You need to check motor side lines for vaccum leaks
  10. spenc938

    spenc938 New Member

    I'm referring to the cut lines that are plugged with screws that I posted pictures of a couple days ago. I'm pretty sure they go to the missing HVAC orb. I'm going to the junkyard in the morning to try and buy one, as well as see how it's supposed to be hooked up.

    I've been trying to check for leaks everywhere... Especially around the intake manifold because there is a whole slew of possible places it could be leaking there (obviously).
  11. spenc938

    spenc938 New Member

    I installed a new (old) vacuum reservoir today. The good news is that I now have full heating and cooling functionality. The bad news is that the check engine light came right back on and the motor still behaves exactly as before. In the morning I'm going to give the engine bay another once over looking for any dried out/cracked lines. If I can't find anything I guess I'll just have to swallow my pride and take it to a mechanic.
  12. spenc938

    spenc938 New Member

    So I was searching for vacuum leaks (for what seems like the thirtieth time) and while I was standing there with the hood open I had a thought... I decided to completely back out the idle adjustment screw. I then went and drove it and it was a LOT better. Before I would put it in neutral and it would always go to about 2300 rpm and just sit there. If I was only at 1200 RPM when I took i out of gear, it would shoot up to 2300 and sit there until I came to a dead stop. But now, while coasting it goes to about 1300-1400. Muuuuch better. It also idles lower, about 870 rpm and the idle is more consistent. I feel like a tard for not trying this before. I looked at it a week ago and thought about adjusting it, but It was barely touching the throttle so I guess I just dismissed the idea. And one more thing, the Ultragauge is now reporting 0 trouble codes and 0 pending trouble codes. So, am I fixed? 870 sitting still at idle still sounds a little high, and this is my first vehicle with a standard transmission so I'm not sure what is considered normal while coasting.
  13. pooleo

    pooleo New Member

    idle on these trucks is around 1,100
  14. spenc938

    spenc938 New Member

    One more thing I forgot to mention. Regardless of setting, the ac/heater still has a little bit of air coming out at the floor. So I think I may have a small leak somewhere, but I think it's going to be pretty tough to find.
  15. maranger

    maranger New Member

    Check ur mass airflow sensor

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