Hi there,

I bought Motocraft spark plugs from the Ford dealer for my car Mustang GT 2005 and decided to install it my self since they are asking too much to install. i did and noticed a bad rough Idle at stopping and while am driving the car is not accelerate smoothly . like there is some lag and the engine noise is higher. i can feel car body is shaking dont know why.

I tried to remove them, clean and make sure it fit. put them back and its the same. the car is shaking while driving. tried to clear MAF and TB but its the same. do i need to GAP the spark plugs even tho its OEM? i called them they said no need to, just plug it and that's it.

what could be the reason? no check engine showing also on the dashboard.

Perhaps you accidentally got some nickel anti-seize on the ground electrodes.

well i didnt even put that one when i removed/ installed the new on first time but am still having this issue. the crazy thing more that its not sending check engine !

it's always a good idea to check the gap even though they are supposed to be pre-gapped

"engine noise is higher" suggests maybe there is a leak . . . if you are going to take them out to check the gap, make sure they are properly torqued when you put them back in

just guessing!

A loose spark plug can sound like a header leak.

Make sure they are torqued to 25lb/ft.(Recheck after a few heat/cooling cycles). Also, did you remove the boots from the coils and clean and relube them with dielectric grease? If you're still have rough idle issues, unplug/plug in each coil one at a time while the engine is running. If you unplug a coil and the idle gets worse then you know its firing. If the idle doesn't change then that cylinder is more than likely not firing. Mark it with tape or marker and come back to it after all 8 have been tested.

From what you've told us so far, Jeramy is right. Start checking to see if you have a bad plug or connection.

Hi everyone,

So i did the thing i hate and dropped my car on the dealer. after couple of days he called me today and said i have to change the Coils pack and the harness wires! ..and then if this didn't work then i have to change the main ECU???
i told him what??? cant you guys see if the Coil has some issues or not without changing it? they want to cost me around 700$ whether this help or not and for sure the same will be for the wires. this stealing!!

am going to take the car from them tomorrow, but is there is any way to check if the coil is weak or the harness is bad? am an IT not cars tech but i have little experience with my car.

did you try what Jeremy suggested earlier in this thread? that would be a good place to start, the intent is to find out which coil (or wire or connection or plug) is bad

They aren't called stealerships for nothing. I advise anyone to always take a tube of KY Jelly with them if they have to pay for repairs at the stealership.
Shadad, I just noticed you're from Doha. I used to live in the UAE and the only time I ever visited Ford was to buy OEM parts.
My advice is to scan the ECU for fault codes. If you don't have an SCT tuner or any other OBD II code reader, buy one. It'll very quickly pay for itself and save you a lot of money. You'll save your friends a lot of money too by scanning the ECU codes on their cars.
I suspect you'll find a misfire code on one or more cylinders even though you don't have a CEL. Finding one would actually be good news because it'll pinpoint the problem. Let us know what you find.

I should have tried this my self first time i agree but you know am an IT not a car tech even tho i changed the AC compressor, Dashboard, installed UDP and the alternator my self :P.

I will pull my car from the company today and pay them the 200$ for nothing. lets see how this will end. its either the Coil or the harness

Hi there
i come to know that late as am now need to pay them the 200$ for checking ( doing nothing excepat wasting my time and money ) and i will pull the car to try the coil troubleshooting at home.
whats driving my crazy that its not showing Engine check so far. I have the OBD II btw. its very nice tool but am not able to find anything or any error on the car. usually i buy from Americanmuscles site my parts and install it my self. I did many stuff to my car myself even tho am an IT not a car tech. i search and learn hehe. i changed the AC compressor, Dashboard, installed UDP and the alternator my self :P. dont know why i was lazy and decided to give it for the local ford here. my mistake that am paid for it.

I will try pull the Coils one by one and see if there is change on the car noise. then i will switched the one that cause the issue to different location just to make sure its not the wire harness of that one. lets see what will happen.

I will update you all after this . thank you.

Why did you decide to change plugs. Was it running rough?
If it was running smooth and you decided to change the plugs just because they're old, then I don't believe one or more coil pack suddenly went bad.
It's gonna take you some time but do what Jeremy suggested. You may have a bad plug or two. If you suspect a plug is bad, while following Jeremy's procedure, swap it to another cylinder and see if the problem moves with the plug. If it does, you know you have a bad plug.

Hi there,
Its because the company recommend me to since the car reached the 100K and that consider part of the major replacements. the car was drive very nice |( maybe some hesitate at 60 speed ) but when i changed it the car performance went very bad.
anyway. i just pulled the car from Ford. they didnt mention anything about the Spark plugs and insist this might be the coils + Harness wires which they want me to pay for it EVEN if the replacement didnt fixed that (crazy people! ).

when i asked the Tech about the Coil he didn't give me clear answer if its the coil or not. what is this?! i even ask him in front of the customer support: is the Coils ok or not? did you checked it?..he was like
Ford standards fall too hard on my country. i can understand about outsource $hit that going on some companies ...but this! ?

i will try the Coil troubleshooting adviced by the friends here on the forum and ...lets see.

Since you say it was running fine before the spark plug change and the problem only came after the change, it is likely you just have a bad spark plug and not a bad coil. The test mentioned above will help you locate which one, but it is good you didn't do what the dealer was saying!