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autodoc_2000, ASE Certified Technician
Category: Mercury
Satisfied Customers: 2563
Experience:  ASE Master Technician, 1999 Ford Senior Master Technician Certification
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1996 mercury grand marquis: check engine light..rough idle..goes away

Customer Question

1996 mercury grand marquis. check engine light was on. really rough idle, which goes away after getting up to about 25-30 mph. hit autozone to have them look at the codes. said there was a misfire on #6. replaced all wires and plugs. it still idles rough, and all the interior lights and dash, and headlights flicker. any ideas while i'm waiting for the check engine light to come back on? (i disconnected the battery to reset the computer after doing the work)
Submitted: 7 years ago.
Category: Mercury
Expert:  autodoc_2000 replied 7 years ago.
Since the plugs and wire have not been changed since new what does the fuel filter look like? This will cause a rough idle and also no power trying to accelerate. What does the air filter look like? A dirty MAF (Mass Air Flow) sensor can also cause this issue if it cannot determine how much air is going into the engine. Also check the PCV hose they have a tendency of rotting and creating a vacuum leak. These engines are known for the valves sucking up into the cylinder head which causes a misfire. Sometimes it can be seen with a compression test and sometimes not. A vacuum gauge hooked up to the engine will sometimes show it also. If the gauge fluctuates there is a valve issue.As for the lights flickering. If the idle is low enough the alternator does not spin fast enough to charge correctly.

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