'98 Mercury Grand Marquis GS, rough idle questions

[_Hacksaw]

Dear forum members.

I have been flattened by legal and medical paperwork and car work here and much more, but finally feel good in returning as new member. Briefly, if one can make such things brief, after fully tuning up my new "used" Mercury with 67k on the OD, I went out to warm it up tonight after washing it yesterday evening here in California as the sun was so beautiful and the weather so glorious ( the very edge of fall and grape harvest ) and what I experienced was troubling ( to me ). No matter how long I warmed this new ( several months old ) Mercury up, I could feel that shake and tremble in the steering wheel at idle and then as the RPMS rose by upping them to 2500 just to see what was what. I could hear what I believed to be a brief dropout or very brief miss and yet at the lower idle I feel this tremble in the steering wheel. I *know* something is not correct with this, so I want to ask where to begin as I am new to this platform and just sold the old '85 Dodge Diplomat police car, finally! I have replaced the platinum plugs, changed the oil, belt and several pulleys and have pampered this beautiful dent free and *wonderful* highway car with new brakes ( ceramic ) with new rear rotors that were oddly all worn out.

I keep wondering if I have clogged ( just one ) injector or something else? Stranger, this may all disappear in the morning as it has in the past, so I am vexed at present but ready to put in all next rebuilt injectors if needed. I just want to be sure that this is where to start with this before doing such as it may very well be something else that needs replacement e.g. the EGR? Great weather for car issues here in N. California, so all is on the table. I just do no have any specialized tools but can drive it over to the store in order and obtain a code read on this car if needed.

Any thoughts will be welcome as I find out just what is what with this wonderful car and simply correct it.

Sincerely;

_Hacksaw

[sly]

if there's no codes... could be in need of injector cleaner. Could also be original plugs and need those. worth checking. If it's coil on plug, there may be a coil getting weak. Check the connections to the coils. If it's coil packs... could need wires. When those coils go... they just die typically, but it could be a weak coil on one side. I don't remember what year they went to CoP's.

[_Hacksaw]

Sly one;

I am going to have that code done today as it's seems to be subtle and I am very sensitive to slight noise and vibration et all. I *did* replace the plugs with new platinum plugs and they have been just fine, however as you mention those coils ( *or one injector ) may be 'weak' or just one might be, and that is delicate. I am used to just having and entire cylinder shut down on me as per a broken spark plug wire on my now recycled Dodge. Nothing subtle about that. I am going to monitor this slight tremble and see how it improves, varies or remains the same across time as this issue has just been set to the back burner as my brake pedal has started to fade at stop when I press it. I have ordered a new one and will pick it up today.

I will ask for any special assistance or instructions with this replacement in the next post, as this needs to be attended to ASAP, with time left on the clock as it's not critical just yet. Something about a bleeder bolt on the master brake cylinder that baffles me at this point. So for today I will see if I can get a code read on this car for the very first time and see if anything else is amiss. It may or may not be periodic, this tremble in the steering wheel and engine, and was told by one mechanic that it was all fine ( the injectors ) so we shall see. I did run *numerous* injectors cleaners through this system including the notorious Seafoam, however I didn't remove them and clean them. All in good time, so for now it's the master cylinder and then the notorious brake bleed!

Many thanks!

_Hacksaw

[79lincolnlover]

Did you wash the engine bay?

[_Hacksaw]

Yes. Multiple times. On Labor Day, of all days to work ( it's was really beautiful here and just perfect for car work) I flushed the all of the coolant, replaced the thermostat, and then flushed the brake fluid 4x. I have a de-greaser for the engine however it's very very clean as this car has been garaged and never taken on long trips. So I have all new tires and brakes and rotors + the new ceramic pads and it really moves well and stops like a demon. This car runs very cool also! There are times when I drive across town and then test the wheel for that mild shake / vibration and it nearly disappears, so maybe it's temperature related? BTW just by replacing the thermostat ( 195 F ) this car runs very cool now. I was stunned at the difference. I suspect it' the aluminium engine. Beautiful cars!

[sly]

if you hosed the engine down... you may have water seepage in the coil packs causing issues. They really don't like water at all.

[Louis]

I'll bet you shorted out at least one of the coil-on-plugs (cops) by washing the engine.

I very cautiously washed my engine bay on my '98 this past spring avoiding getting water anywhere near the top of the motor....must have had some inadvertant splash, enough to short out 1 cop at the rear of the motor.

[_Hacksaw]

Louis and "The Sly One';

What were the clear and obvious presenting symptoms of this simple human error? I mean did this car *really* shake and miss in one cylinder? If so that would make it pretty obvious vs. the subtle shake at idle that I have off and on. There are times when warm ( hot ) when this car is sooooooo silent and there is no such slight tremble in the steering wheel that I believe the car's engine is off ( it's not ). There is also so much heat involved here, just by virtue of parking my car in the sun in California, that there is no way that any H2O could be present at this time. Oddly, I forgot to apply dialectic grease when I replaced those plugs. Crazy job BTW. I *did* use anti-seize and am glad that I did as I did hear these plugs chirping and squeaking when I removed them from the block.

I have put all car work on full *Hold* at this as per my Labor day "Day After" experience! The insides of both my left and right arms became beet red and inflamed ( again ) by a reaction to the anti-freeze and or brake fluid. Total hell! The 1% Hydro-cortisone cream only made it worse for the first week before it finally started to quiet down at night. Then came the skin peal that is almost over with. While it's almost back to it's normal color, it's still red and sensitive. Maybe it was the brake fluid? It got me like this about ten years ago and yet it was not this bad then ( the pain! ). At least I got all fluids flushed, but what a surprise price tag. Yuck. I do not recommend this for anyone with sensitive skin.

_Hacksaw

[sly]

most the time it's a weak spark issue instead of a pure misfire event. That's the reason it doesn't throw a code. And for a subtle shake I wouldn't worry. My car with it's 03 CoP engine rattles like crazy all the friggin time at idle due to the tune... it's just less pronounced when at operating temp. It should really only be a concern for you when you can feel more of a buck with the trans in park/neutral. Stumbling is when the coils should be replaced. My bet would be on carbon build-up and maybe just the need for a good workout (Italian tune-up) and/or injector cleaner.