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    #1

    Extremely high idle problem

    Hey mangs, sorry I haven't been around much, just ben busy with school.

    Was driving the marquis the other day on the highway when i noticed the engine temp was low (150). Seemed kind of odd so I made sure the fan was off, turned off the heater and took it out of overdrive to see if it would go back to normal. Nothing was making it go back up so I decided to stop and just sit for a few minutes, but as I was slowing down (~25mph) I noticed it was very hard to stop and the rpm's were still up near 2000. When i put it in park the rpm shot up to 3300 and wouldn't settle down. Looked around for any obvious vacuum leaks and smacked the IAC a few times but no change. Looked around a bit more, checked the fluids and made sure the throttle wasn't just sticking but couldn't find the problem. Was out in the middle of nowhere so just decided to keep driving, it was another 70 miles or so before i got home. The issue still persisted, although at highway speeds nothing seemed out of the ordinary other than the temp still staying down.

    Pulled the codes this morning, memory showed an ACT out of range, and ECT out of range code. Checked both sensors while plugged in and they read exactly as they should at that temperature.

    Pulled the cruise servo cable off, no change.

    Blew some smoke into the intake manifold through a hose to check for vac leaks and found none. Hooked up the vac gauge and while idling at 3300 it was a steady 21 inches.

    Pulled the IAC off and cleaned it out, though it wasn't very dirty and seemed to be moving properly. Reinstalled but still @ 3300 rpms. When i pull the IAC plug the idle drops to a steady 1900 rpm.

    Checked the TPS but it was perfect. (.97v @ closed throttle)

    Pulled the vac line at the fuel pressure regulator, no fuel leaked out. Hooked up the fuel pressure gauge, got 33 psi after priming the pump, and ~30 psi @ 3300 rpm.

    Removed the map sensor and checked it with an oscilloscope and vacuum gauge. Frequencies matched the specs on http://oldfuelinjection.com/?p=27 perfectly.

    Distributor was still tight, and according to the marks I made at the base, hadn't moved at all. Spout connector was still there.

    If i start it and hold my finger over the inlet to the IAC I can get the rpm's down, so it sort of seems to be an issue with the IAC. I installed another IAC from some other ford which when unplugged brought the rpms down a little more than the other to ~1600. Has a different plug, so wasn't able to try it plugged in.

    With the IAC unplugged should it even run at all? Seems like the spring should hold the valve completely shut letting no air through... unless the manifold vacuum is stronger than the spring and is sucking it open?
    Everything seems to point to the engine getting more air than it needs, however the IAC doesn't seem like the definite problem.

    Don't really have the money to spend on a new IAC that may not fix it so I wanted to see if any of you had some other ideas, thanks in advance...

    -Mark


    1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
    1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
    1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)
    Tags: None
    #2
    If it idles at 1600 with the IAC unplugged, that sounds like a fairly big vacuum leak somewhere. A failed brake booster might do this.

    Good to hear from you again. Thought you died or sold off all your cars and were hiding in shame for driving a Kia or something.
    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC grandpa spec white and cranberry

    1984 Lincoln Continental TurboDiesel - rolls coal

    Originally posted by phayzer5
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

    Comment

      #3
      I'll check out the booster and hose, although both are only a couple years old, same as all the vacuum lines under the hood.

      With that big of a leak would i still be pulling 21 inches of vac?

      Yep, still around Thain. Still as addicted to these cars as ever, just don't have as much time/money to tinker until i'm done with school.


      1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
      1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
      1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)

      Comment

        #4
        Originally posted by FatNasty View Post

        Don't really have the money to spend on a new IAC that may not fix it so I wanted to see if any of you had some other ideas, thanks in advance...

        -Mark
        You can try cleaning the spring with some WD-40 and an old toothbrush.

        Comment

          #5
          Got a new IAC to try, behaved exactly as the old one did both plugged in and unplugged.

          Booster seems ok, pedal is firm when pressed with engine off, then as it starts pushes in a bit more with the vacuum assisting. Exactly as it felt before the problem.


          1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
          1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
          1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)

          Comment

            #6
            hm, wouldn't expect to see 21" vacuum with a major leak, but theres really no other way for it to have a high idle with the IAC unplugged unless air was being pulled in from someplace.

            Stupid question, but you didn't by chance have to plug an air bleed hole in the throttle blade did you? I seem to remember having to do that on some car with some combo of crap but I don't remember what or why. If you did that, make sure the plug is still there.

            and the overly cold temperature thing, possibly your thermostat stuck open. I don't expect that should cause a high idle but it would cause the out of range codes if the motor wasn't warm enough.
            86 Lincoln Town Car (Galactica).
            5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

            91 Lincoln Mark VII LSC grandpa spec white and cranberry

            1984 Lincoln Continental TurboDiesel - rolls coal

            Originally posted by phayzer5
            I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

            Comment

              #7
              Thats exactly what I was thinking, if the IAC is unplugged air has to be coming from somewhere, so when I covered the throttle body opening with a book and it still didn't die I knew there had to be a leak somewhere in the manifold. BTW, my throttle blade does have the air bleed hole, but i never plugged it to begin with and all was fine.

              Made sure the throttle body nuts were tight, they were.

              Pulled the EGR to make sure the diaphragm hadn't torn or something, but it was fine.

              Then I decided to tighten down the upper manifold bolts and found 3 of them spinning in the hole. Looks like they were only catching about 3 threads and had recently (presumably) let go. Seems like a lot of air getting through what must have been a very small space since the other 3 bolts weren't loose, but it would explain it. Either way, needs fixing so I pulled the upper intake and will go searching for longer bolts tomorrow. Luckily there is still about a half inch of good threads on the lower intake.


              1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
              1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
              1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)

              Comment

                #8
                yeah that might do it. Worst case, allthread and a nut will hold it together. Actually that might be an even better solution since you know you'd have full thread engagement in the lower intake.
                86 Lincoln Town Car (Galactica).
                5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                91 Lincoln Mark VII LSC grandpa spec white and cranberry

                1984 Lincoln Continental TurboDiesel - rolls coal

                Originally posted by phayzer5
                I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                Comment

                  #9
                  Found the correct bolts on amazon, bought a pack of 5 but of course only one showed up. Needed the car so I did go with allthread/nuts on 3 of them. That and a couple new gaskets and its running fine again.
                  Low temp issue seems to have resolved itself as well. Rest of the bolts should be here friday, just glad to be out of the cold.


                  1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
                  1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
                  1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)

                  Comment

                    #10
                    curious that you had 21" vac AND that big leak, but looks like you found it! congrats!

                    Comment

                      #11
                      did you get this fixed?

                      I had a similar problem with my Explorer intake. come to find out there several different length bolts for the upper intake. Unknowingly, I used the shortest ones and pulled the threads out of 3 of the holes. Helicoil to the rescue and I found the correct length bolts, problem solved.
                      2003 Town Car Signature - 3.27 RAR, Dual exhaust and J-mod - SOLD 9/2011
                      89 Crown Victoria LX HPP -- SOLD 9/2010
                      88 Grand Marquis LS - The Original -- Totaled 5/2006

                      I rebuild AOD/AODE/4R70W/4R75E transmissions....Check out my Facebook page: https://www.facebook.com/pages/North...48414635312478

                      Comment

                        #12
                        Yep, correct bolts and some fresh gaskets fixed the problem. I had used the bolts that came with the intake spacer, but they were still too short. I'm assuming they might have only worked properly for the tubular gt40 intake or something. Explorer intakes need (4) 5/16-18 bolts 7 inches long. Hardware stores top out at about 6" or 6.5" so had to get them from fastenal. The 2 short bolts were fine.


                        1984 Grand Marquis GS - CFI-SEFI conversion, Explorer 302, GT40 intakes, GT40P heads, 1.7 roller rockers, HO Cam, ASP Underdrive Pulley, 2.5" Dual exhaust, Flowmaster Delta 50 mufflers, 3.55 Trac-Lock, Rear disk's, Moog cargo coils, ES rear poly bushings, PI front and rear sway bars, 3G alt., Mark VIII fan, custom Auto-meter dash
                        1990 Crown Victoria Country Squire - Explorer 302, HO cam, dual exhaust, 3.55 Trac-Lock, PI rear sway bar (SOLD)
                        1982 LTD Wagon (R.I.P.) -|-1984 Grand Marquis LS(R.I.P.)

                        Comment

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