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)
Year : 1996Make : MercuryModel: Grand MarquisEngine: stock v8 (vin code W)
Ok, a bit of background. It was intermittenly idling rough. Goes away after getting up around 25 mph. It got to a point where it idles rough all the time, and pretty bad too. The whole car shakes. I zipped over to Autozone to pull the codes, and was told there was a misfire on cylinder 6. (i never actually got to see the codes on his checker). So, a week later I hit the other auto part store, and picked up plugs and wires. It turns out that I replaced the originals, and this car has 121,000+ miles on it. (dang grandparents!!)I never drive the thing, so never knew how bad it was. Ok, so now we've solved the bad plug issue. The car still idles rough, and upon sitting inside the car, i noticed that every light flickers when she idles rough. When she runs ok, no problem with flickering. (everything flickers, dash lights, door lights, even the headlights. clock on the radio too). I think it's all related, but am not sure where to begin. As far as running, from a dead stop i can floor it, but get no response from the motor. However, if i just goose the pedal bit by bit, she'll get up to speed, and then be ok.
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.