High Idle and Thumping Breaks after Fuel Pump Replacement
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Northstar Engines and System Technical Discussion Discussion, High Idle and Thumping Breaks after Fuel Pump Replacement in Cadillac Engine Technical Discussion; Hello, My 94 SLS had a fuel pump go bad. I didn't experience any other problems other than hard starts ...
  1. #1
    thejohnson is offline Cadillac Owners Member
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    High Idle and Thumping Breaks after Fuel Pump Replacement

    Hello,
    My 94 SLS had a fuel pump go bad. I didn't experience any other problems other than hard starts when cold before it just wouldn't start anymore. I replaced the fuel pump and got the car running again. However, I have a very high idle now (2k to 2500 rpms). It's so bad that the car will slightly gain speed going up a hill without using the accelerator. Going down I have to ride the brakes pretty good to not exceed the speed limit on the road.
    I had one code which was P036 - EGR. I took it out and cleaned it. At first it seemed a little stuck in the closed position. It may still be a little sticky but I can push the valve open pretty easily with a screwdriver and it closes when i remove the screwdriver.
    I think the thumping breaks may be due to jacking up the car so many times to do the fuel pump but read somewhere that a leaky power brake booster can cause a high idle as well.
    I saw neither of these problems before I replaced the fuel pump. Any help would be greatly appreciated.

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Clean the EGR until there is absolutely no sticking.

    When was the TB last cleaned? The throttle plate may not be closing. Check to see if the throttle is resting on the ISC plunger when it is idling high. If it is not, then it's the TB.

  4. #3
    tateos's Avatar
    tateos is offline Cadillac Owners Connoisseur
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    The thumping brakes may be from warped rotors, made worse because you are riding the brakes to keep your speed down...

  5. #4
    thejohnson is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    The TB is not resting on the plunger. Also, the TB appears to be clean and moves freely from open to close when I move it manually when the car is off. It appears as if a motor is controlling the throttle because I can see a smooth jerking motion as it comes down from high rpms....while driving when I put in neutral it likes to stay higher around 3k rpms. Is there any sensor or device that could be controlling the throttle?

    Thanks,

  6. #5
    Mark C's Avatar
    Mark C is offline Cadillac Owners Connoisseur
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Vacuum leak will cause a high idle, if it backfired previous to the high idle condition starting you may have blown the backfire preventor valve off its seat. that will cuase a huge vacuum leak and a very high idle condition. My 97 did it once and it would bounce off the high speed fuel cutoff around 4K rpm.

  7. #6
    Ranger's Avatar
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    When the engine is off, the plunger is retracted and will not contact the throttle lever. Check it at idle. Also pull the DTC's.

  8. #7
    thejohnson is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    I did have a backfire just before I replaced the fuel pump. I hadn't gotten it started since it happened. Great Clue. Where is this valve located? THANKS

  9. #8
    Ranger's Avatar
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Never heard of a backfire "prevention" valve. Maybe Mark meant the over pressurization valve, but your engine doesn't have one. Over pressurization pressure relief on your engine ('93's and '94's) is provided by the intake manifold cover lifting slightly to vent the pressure. Pull the cover and check the seals, but get the torque values before putting it back together and don't over torque it or you'll no longer have that over pressurization ventilation capability.

  10. #9
    thejohnson is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Thanks for the info. I took off the intake cover and found the seal is broken. It appears it came apart in a few spots but the one on the left there wasn't a piece that I could find and may be the culprit. Is there a gasket compound I can use to repair this? Just trying to get this car running so I can trade it in. If a gasket compound simply will not work, do you know where I can get another seal? Thanks!!
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    Ranger's Avatar
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    I think it is safe to say that was the cause of you high idle. Might try rockauto for the gasket. If no luck, then gmotors.com

  12. #11
    thejohnson is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Thanks Ranger. I'm having a difficult time finding anywhere that has this seal or gasket...even on GM sites. I've got an E-mail into them to see if it is available. Do you have a recommendation on a permatex like compound that would possibly fix it temporarily? I was thinking #2 Permatex (gasket sealer but more focused on sealing than an adhesive). What are your thoughts?

  13. #12
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Take a look at the Permatex RTV silicone which GM uses for the newer halfcase and oil pan seal compound. It should effectively bridge those gaps in the manifold cover.

    Make sure you clean the gaps with alcohol - not rubbing alcohol (it has glycerin in it) - use either ethanol (grain alcohol) or a bit of methanol ( hardware store, in cans).

  14. #13
    Ranger's Avatar
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Keep in mind that the cover is supposed to lift off of the manifold to vent any over pressurization in the event of a backfire. I guess an RTV like Sub mentioned would work, but if I went that route, I'd lay a bead and let it set up a little bit. Then I'd put some grease or Vasiline on the manifold so it would not stick to the RTV and set it in place with very light pressure to form the mating surface, but would not torque it until it had completely set up, thereby "making" a new seal that should operate as intended (if done properly).

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    tateos's Avatar
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Right off the Rock Auto website:

    FEL-PRO Part # MS93225 {Set}
    DOHC Engine


    $40.79

    ACDELCO Part # 17090990
    GASKET,INT MANIF CVR
    * Non-stock item--shipping delayed up to 5 business days

    $110.79 $0.00 $110.79
    Add to Cart

  16. #15
    thejohnson is offline Cadillac Owners Member
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    Re: High Idle and Thumping Breaks after Fuel Pump Replacement

    Hey thanks for checking tateos. However that's the lower gasket set. Unless nobody is including the upper seal in their picture...

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