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1986 Grand Marquis Engine Keeps Dying While Starting and Switching Gears

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    #1

    1986 Grand Marquis Engine Keeps Dying While Starting and Switching Gears

    So here’s the problem. Every time I try to start my car, the engine dies, unless I hold down the accelerator, and give it some gas. If I try to switch it into drive or reverse, it dies, unless I’m giving it gas while I switch gears. I was stuck in a mall parking lot an hour from home most of tonight… it was not fun at all, to say the least. I pretty much had to start it, hold the key fully engaged while I held down the gas for a bit, then I had to quickly switch it into drive while still giving it gas… which I know is not good for my car at all…

    However, when I get it into drive (or reverse for that matter), the engine will stay alive, even if I’m idling. But as soon as I switch from drive to reverse, or to park, the engine will die again. I know when you switch from park to reverse and drive and vice versa, that your RPMs go drastically down… I guess they are going down enough to kill the engine… I suspect this means it’s a vacuum problem?

    When the engine dies, the battery light will come on, as well as the engine light.

    Also, when I make a sharp turn, the engine tends to die as well.

    I’ve had this problem for about a week. I assumed that it was a vacuum problem, so I checked all 5 vacuum lines that lead to the upper intake (4 that go into it from the back, and 1 from the front). The connections were all pretty frayed, so I replaced them… the one that goes into the intake from the front has a pretty decayed line… There might be a leak in it, but I’m not sure…

    Anyways, after I replaced those connections a few days ago, every thing seemed to work fine for a day… but then the problem quickly started again….

    When I was doing repairs, I removed and replaced the following to get to the vacuum lines - The air filter, the upper intake, and the connector that connects the air filter to the intake (that metal part that's circle, and has that hinged brass colored metal door in it). I also removed the IAC and cleaned it out, just in case.

    So to my best guess, I fiddled with something that was contributing to the problem, and it made it better for a little bit… But, I don’t know… I’m really almost out of patience with the old Grand Marquis…

    What do you guys think could be causing this problem? Vacuum lines? Transmission? The battery?

    I’ve been trying to check each vacuum line, but I really can’t see if one has any leaks… Is there any specific line I should be looking at? I assume the ones that go into the intake are the most important ones…

    I would really appreciate any help, and if you need any more information to help me solve this, I’d be glad to give it!

    It’s a 1986 Grand Marquis 5.0 LS with EFI….
    1986 Mercury Grand Marquis 5.0 LS, named "Ulysses "

    Tags: replace IACV
    #2
    That happened to me when i brought my car home the day i got it. Turned out to be the Idle air control valve on mine. Grabbed one from the local yard and it stopped dying out when id switch gears.
    2018 F150 XLT 43k
    1970 Buick GS 455 Stage 1 44k
    1968 Buick Riviera

    Comment

      #3
      Sounds like an IAC to me as well.
      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

        #4
        I’ll take off the IAC again and give it a good scrubbing… hopefully that’ll help. If not, you can pick up a new one for about 50 bucks, right?

        Also, I had an idea… since the engine dies when switching gears… could this be directly because of a bad vacuum line that goes directly to the transmission?
        1986 Mercury Grand Marquis 5.0 LS, named "Ulysses "

        Comment

          #5
          My '86 CV had the same problem. If you take the IAC out again, spray the inside out with carb, brake, or throttle body cleaner until it's silver. It seems as if the valve inside gets gunked up with oil. If this doesn't help, try cleaning the throttle body blade as well, or just do that anyways. After that, your guess is as good as mine. Perhaps a new IAC.



          Packman

          Comment

            #6
            No vac line to the transmission. Its controlled purely with that cable on the throttle lever.

            never bought a new IAC but i think they're around 50 bucks. I've had fair luck cleaning them in the past or just swapping them with ones from the junkyard that looked shiny.
            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
              My car would stall when starting unless you put it into drive right away. Turned out I had several of those formed plastic vacuum hoses for the emissions system and fuel pressure regulator broken. Replaced those and it was fine.

              Finding out if it's IAC is simple. Use the throttle stop screw to open the throttle a little bit. If that fixes your problem, then the IAC is to blame. If not, then it's something else.
              Originally posted by gadget73
              There is nothing more permanent than a temporary fix.
              91 Mercury CP, Lopo 302, AOD, 3.08LSD. 3g upgrade, Moog wagon coils up front, cc819s in the back. KYB GR-2 police shocks. Energy suspension control arm bushings. Smog deleted.
              93 F-150 XLT, 302, ZF 5-spd from 1-ton, 4wd.
              Daily--07 Civic Coupe. Bone stock with 25k miles
              Wife--14 Subaru Outback. 6-speed.
              95 Subaru Legacy Wagon--red--STOLEN 1/6/13

              Comment

                #8
                And where exactly is the throttle stop screw located?
                1986 Mercury Grand Marquis 5.0 LS, named "Ulysses "

                Comment

                  #9
                  on the throttle body.
                  ~David~

                  My 1987 Crown Victoria Coupe: The Brown Blob
                  My 2004 Mercedes Benz E320:The Benz

                  Originally posted by ootdega
                  My life is a long series of "nevermind" and "I guess not."

                  Originally posted by DerekTheGreat
                  But, that's just coming from me, this site's biggest pessimist. Best of luck

                  Originally posted by gadget73
                  my car starts and it has AC. Yours doesn't start and it has no AC. Seems obvious to me.



                  ​

                  Comment

                    #10
                    the throttle lever sits against it when the throttle is closed.
                    Originally posted by gadget73
                    There is nothing more permanent than a temporary fix.
                    91 Mercury CP, Lopo 302, AOD, 3.08LSD. 3g upgrade, Moog wagon coils up front, cc819s in the back. KYB GR-2 police shocks. Energy suspension control arm bushings. Smog deleted.
                    93 F-150 XLT, 302, ZF 5-spd from 1-ton, 4wd.
                    Daily--07 Civic Coupe. Bone stock with 25k miles
                    Wife--14 Subaru Outback. 6-speed.
                    95 Subaru Legacy Wagon--red--STOLEN 1/6/13

                    Comment

                      #11
                      Its not really something you should ever need to mess with, so pay attention to how much you move it so it can be put back.
                      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

                        #12
                        Well, I spent the whole day fiddling with my car. Replaced a ton of vacuum lines… plugged a few that I couldn’t figure out where they went… And toyed with capping the emergency brake auto release line, but it didn’t seem to have any affect. I cleaned out the IAC with carb spray, and I think I got it pretty clean… but when I placed it back on an fired up the engine, it started making a weird ticking sound… it was pretty quiet, but defiantly not there before…

                        Anyways, the problem is still occurring, but less now… Seems that if I switch from park to drive or reverse REALLY quickly, it doesn’t die… but it I switch slowly, it does…

                        Sometimes, I still have to give it gas while doing this to keep it alive…

                        I’m going to pick up a brand new IAC tomorrow morning, and see if that does anything. Before I put it on, is there anything I should know about doing that? Can you just take off the old one, and put on the new one as easily as that? No extra little tricks?

                        If it’s not the IAC causing this mess, I don’t know what it is… maybe a vacuum leak I couldn’t find, or something else…

                        Oh, I checked the RPM’s… looks like it’s getting about 500 when idle…

                        Could this be ignition related? This problem I’m having?
                        1986 Mercury Grand Marquis 5.0 LS, named "Ulysses "

                        Comment

                          #13
                          how does the car run when warmed up? And 500 is too low. It should be around 700ish. Also check the ACT sensor on the drivers side on the lower intake manifold, they get crudded up and start doing weird things when it's cold starting. If you haven't given the car a tune up in a while, it would not hurt to do it. But first raise the idle, it sounds like someone messed with that throttle screw.

                          Comment

                            #14
                            Is the ACT sensor easy to get to????? Or would I have to take off the upper and lower intake to get to it? I certainly hope it’s easy to reach… Scraped up my hands bad enough with all the tinkering over my engine today, hehe.

                            Yeah, I think I'm going to replace all the lines that come off the spark plugs... plugs are good, just under a year old... but I've noticed some chuncky white crud in the lines where they connect to the spark plugs... might as well go do a full tune up soon with fuel filter, oil change and whatnot...
                            Last edited by WilliamFredrickson; 11-11-2009, 04:35 AM.
                            1986 Mercury Grand Marquis 5.0 LS, named "Ulysses "

                            Comment

                              #15
                              ACT is on the lower intake, behind injector #5. Very easy to access.

                              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

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