engine shaking above idle rpm

Hi@all,

I go crazy with my 1999 Mustang cobra, it has no mods, all factory .
At idle rpm it runs smooth, if I raise the rpm the engine begins to shake or vibrate, at 1.200 to 1.400 it is worst. If I raise to 2.000 or 4.000 it will be better, but I feel the vibrations . All with the car in park, clutch pressed or not.

I installed new plugs, new ignition coils, cleaned MAF, checked EGR .
Then I noticed that the vibrations at 1.200 to 1.400 are when I raise the rpm AND when I raise to 2.000 rpm and then take the foot from the acceleration and the rpm fall to the 1.400 to 1.200 the vibrations are still the same, so I think it is a mechanic problem ??? because at falling there is no power required???

I also installed a new flywheel with clutch.

Now I am at the end, I would swap the harmonic damper or the engine mounts, but not sure... don´t think that it is a fuel/air or ignition problem, because I raised the rpm to 2.500 and then turn off the engine , the shaking comes up again when falling down the rpm.


I hope anybody can help....

thanks and all the best from europe

Kay

How many miles? I had to replace my engine mounts at 167k miles on my 99 cobra. Maybe take a look at those real quick.

check to see if you installed the maf backwards, there is an arrow which indicates flow direction. it's a Long shot but actually happened to me when installing a Cold air intake


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I checked, the arrow look right to the throttle body.
thanks.

forget to say, also cleaned the throttle body.
There are no codes stored and I checked some live datas on OBD, can´t find any weird datas.

Did the vibration start after you did the clutch install?

No, the vibrations start before.
I changed the clutch because the one which was installed was very hard and I hoped that a new flywheel could end the vibrations.... But no change on vibrations.

Is it a vibration or is the engine actually shaking? Bad motor mounts won't cause the engine to shake. However, bad motor mounts can cause the exhaust to touch the body somewhere which will cause all kinds of weird feelings. Went through this not too long ago with my son's car. He kept telling me about this weird vibration at certain RPM's. I told him to check his exhaust. Low and behold the passenger side of the mid pipe was touching the K member. We also recently found out the motor mounts were completely shot. Like not really there anymore shot.

It is a vibration, when sitting in the car and rev to 1.200 rpm you feel vibrations and you see the steering wheel trembling. Outside with the hood open, same rpm, you can see the hood trembling, engine not really, only very slight. Like slightly bad coils or so.....

What plugs and COPs did you go with? There's a chance you got a bad plug in the bunch.

I put in iridium plugs and new set of msd blaster cops. No difference to the old Motorcraft cops and plugs.

Get rid of the MSD COP's. Aftermarket COP's are worthless on these cars. The stockers are the best choice. Even when boosted. Personally I'd try a set of basic copper plugs with the gap double checked. Have you checked for vacuum leaks?

slo984now said:

Get rid of the MSD COP's. Aftermarket COP's are worthless on these cars. The stockers are the best choice. Even when boosted. Personally I'd try a set of basic copper plugs with the gap double checked. Have you checked for vacuum leaks?

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funny you should mention that..my cops are original motorcrafts with over 100k and still running fine.

shurur said:

funny you should mention that..my cops are original motorcrafts with over 100k and still running fine.

Click to expand...

I ran the stock COP's on my 01 till well over 100K. That was dealing with a few different combinations. I picked up a spare low mileage set to fix what I thought was a misfire, but that wasn't the case. So the original set went back into the 01. My 04 currently has the spare set because I was getting a miss under boost. I did all 8 because I didn't want to deal with tracking down the misfire since it wasn't leaving a code. No problems yet.

Hm... OK I will swap to copper plugs, which one would you recommend for a stock engine fromm 1999?

I'm a fan of NGK. Currently have them installed in 2 vehicles and a boat.