RPM's fluctuate while driving.
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Cadillac Seville / Cadillac Eldorado Forum Discussion, RPM's fluctuate while driving. in Past Cadillac Vehicle Discussion; RPMs will drop to 500 then immediately pick back up.spark plugs were just changed about a month ago....
  1. #1
    waitingfordark25 is offline Cadillac Owners Member
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    RPM's fluctuate while driving.

    RPMs will drop to 500 then immediately pick back up.spark plugs were just changed about a month ago.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: RPM's fluctuate while driving.

    Study and practice pulling trouble codes from your car's built-in code scanner system. Use the sticky post ^^^ "How to pull codes". Write down any codes found and whether each is Current or History. Return to the sticky to open the link with "obd2" in the address - that takes you to a Master Index of all P,B,C, and U codes. Decipher any codes found, write it all down and post it all here.

    We assume you used AC Delco #41-987 Platinum plugs ? If not, all bets are off.

    Clean throttlebody and all intake air ducting tight and leak-free from the MAF to the TB ?

    For pictures and diagrams of your engine and some car parts, click my username, open the profile. 2 albums, 6 pages in the left column.

  4. #3
    sts 03's Avatar
    sts 03 is offline Cadillac Owners Connoisseur
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    Is this when you are coming to a stop? My car does the same thing sometimes when coming to a stop the rpm drops to 500 then goes back to normal.if you do figure it out please post (I'll do the same)

  5. #4
    waitingfordark25 is offline Cadillac Owners Member
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    I've got a black kind of L shaped piece that fits over my air filter and connects to a hose but I noticed when I checked my air filter that piece loosely fits in the hose.it looked like at one time it was sealed in there, could that be causing the problem? The car runs fine, it doesn't shake when idling or anything. I can't even tell the RPMs are dropping just by looking at the gauge.

  6. #5
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    That's the resonator. A vacuum leak there (or anywhere before the MAF), will allow unmetered air into the engine, throw off the air/fuel mixture, and cause idle, and possibly drivability problems.

    The resonator needs to be seated properly, and securely into the intake ducting. Or better yet, remove it and plug the hole. Do a search for the "butt plug mod". Getting the resonator out of the way makes several maintenance procedures much easier.

  7. #6
    sts 03's Avatar
    sts 03 is offline Cadillac Owners Connoisseur
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    Yeah there is supposed to be a screw type clamp on there to keep it tight.

  8. #7
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    There's a narrow, one time use clamp on there from the factory. A radiator hose clamp didn't work for me, it was too wide, and didn't allow the resonator to seat properly. It kept sliding out.

    The purpose of the resonator is to reduce induction noise. I notice no difference with mine removed. Do the mod mentioned above, and be done with it.

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