# Grand Marquis shuddering

**URL:** <https://community.cartalk.com/t/grand-marquis-shuddering/77747>\
**Category:** Maintenance/Repairs\
**Tags:** mercury, grandmarquis\
**Created:** [March 3, 2013, 3:23am UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747 "2013-03-03T03:23:58Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![logan](https://avatars.discourse-cdn.com/v4/letter/l/278dde/32.png) [@logan](https://community.cartalk.com/u/logan)\
**Post date:** [March 3, 2013, 3:23am UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747/1 "2013-03-03T03:23:58Z")

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My ‘03 Grand Marquis “shudders” when I accelerate, especially up hills. It feels like it cuts in and out momentarily, shaking backward and forward. Here is what I have had done, based on mechanics’ advice: replace spark plugs, replace fuel filter, clean throttle body, clean mass airflow sensor. It still does it after all this and I am stumped.

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**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\
**Post date:** [March 3, 2013, 4:03am UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747/2 "2013-03-03T04:03:42Z")

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Have you changed the transmission fluid and filter?  
Please post any stored fault codes.

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**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\
**Post date:** [March 3, 2013, 7:56am UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747/3 "2013-03-03T07:56:54Z")

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Usually, a misfire causes the CEL to come on and log a trouble code…Usually it will point out which cylinder(s) are miss-firing…Armed with that knowledge, replace the suspect coils…Have you washed the engine lately? Big no-no on these engines…If it has not yet caused the CEL to come on, next time it happens, maintain hard acceleration until it does, then read the codes…The plug-wells should be bone dry. Is that how you found them?

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**Author:** ![nw2012](https://avatars.discourse-cdn.com/v4/letter/n/cc9497/32.png) [@nw2012](https://community.cartalk.com/u/nw2012)\
**Post date:** [March 3, 2013, 9:03pm UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747/4 "2013-03-03T21:03:17Z")

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While it could be a problem with the transmission or other drivetrain components, my first guess, based on what you have replaced, would be that you have a misfire on one or more cylinders.

If that’s the case, try to figure out which cylinder the misfire is on. This car has a Coil-On-Plug system instead of a main ignition coil, so those would be a prime suspect in this case. And, if this car has spark plug wires (I think it does, but really don’t remember. Maybe someone else could correct me) then I would certainly change those every time the plugs are changed.

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**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\
**Post date:** [March 3, 2013, 9:52pm UTC](https://community.cartalk.com/t/grand-marquis-shuddering/77747/5 "2013-03-03T21:52:29Z")

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The car definitely has coil on plug.