M3/4/5 slightly rough idle. Is the cause LTW FW and stiff transmission mounts?

[radialaced]

Would a LTW flywheel and stiff transmission mounts, ( along with the short shifter) cause the car to have a little bit of rough idle that goes away as you rev up?

I know that these changes enhance the engines ability to rev up an increases the accuracy of the shifting, but I'm not crazy about the slight vibration at idle.

It also has underdrive pullies, and at idle I can tell the power steering has to work harder. Not sure about the alternator pully but it does engine does give an extra vibration or two when you increase your demands on electrical power.

I believe the components are UUC.

So, in stock form does an M3 idle as smooth as velvety as my old 328is does?

Thanks

[///Maniac]

If you have a Underdrive CRANK pulley and LTW fly, there's your problem. No harmonic balancer = major wobblage.

The LTW fly will chatter and the stiff tranny mounts will cause some NVH. Have you checked your motor mounts lately? If you have a torn or butchered motor mount, that will cause a major shake.

Jonathan

[L3000C]

i think you should replace your engine mounts with some OEM ones, see if that helps....

[radialaced]

If you have a Underdrive CRANK pulley and LTW fly, there's your problem. No harmonic balancer = major wobblage.

The LTW fly will chatter and the stiff tranny mounts will cause some NVH. Have you checked your motor mounts lately? If you have a torn or butchered motor mount, that will cause a major shake.

Jonathan

I understand.

No underdrive crank pulley here.

It's not a major shake, just a vibration in the butt during idle.

So it is possible for an M3 to idle as smooth as velvet?

[interossiter]

I recently moved from a '97 328is to a '98 M3 w/ 67K miles. One of the first things I noticed was that the M3 idled a little rougher, especially in comparison the the 328 which was super-smooth. I don't know if rough is even the right word, it's just different - a little snap-crackle-and-pop under the hood of the M3. IMO it appears to be a normal difference.

[///Maniac]

So it is possible for an M3 to idle as smooth as velvet?

No. The LTW fly is gonna cause a rattle/shake. If you want velvet, put it back to stock. The extra 15lbs you've saved on your flywheel is one of the MAJOR harmonic dampeners in the car. Pick it up and you'll see what I mean.

Jonathan

[radialaced]

No. The LTW fly is gonna cause a rattle/shake. If you want velvet, put it back to stock. The extra 15lbs you've saved on your flywheel is one of the MAJOR harmonic dampeners in the car. Pick it up and you'll see what I mean.

Jonathan

I might do that. The seller/dealer said he would put it back to stock for free if he can keep the uuc.

Btw, this is a car that I'm buying this week.

Do you think I should take it with the LTW FW and spend some time with it that way? Or just go ahead and have him change it out right from the start?

[radialaced]

I recently moved from a '97 328is to a '98 M3 w/ 67K miles. One of the first things I noticed was that the M3 idled a little rougher, especially in comparison the the 328 which was super-smooth. I don't know if rough is even the right word, it's just different - a little snap-crackle-and-pop under the hood of the M3. IMO it appears to be a normal difference.

I see.

Isn't the 328is a great car? What a motor! Too bad it doesn't have around 40 more horsepower and torque:cool

That's low mileage you have on your M3, I hope you enjoy it.

RAd

[///Maniac]

Daily driver only to the office and back? Travel with the family on vacation? Grocery getter and picking up the kids from elementary only? Go back to stock.

If you're going to autocross it, track it, hillclimb it, etc, keep the LTW fly as it's fantastic for spirited driving and heel toe.

If you're not into spirited driving or don't know what heel toe is and don't care, back to stock.

Letting him keep the UUC flywheel is a good deal for you. Changing a flywheel is a PITA.

Jonathan

[JamesM3M5]

Would a LTW flywheel and stiff transmission mounts, ( along with the short shifter) cause the car to have a little bit of rough idle that goes away as you rev up?

I know that these changes enhance the engines ability to rev up an increases the accuracy of the shifting, but I'm not crazy about the slight vibration at idle.

It also has underdrive pullies, and at idle I can tell the power steering has to work harder. Not sure about the alternator pully but it does engine does give an extra vibration or two when you increase your demands on electrical power.

I believe the components are UUC.

So, in stock form does an M3 idle as smooth as velvety as my old 328is does?

Thanks
Yes, smooth as silk. The LTW FW and trans mounts don't help, but how well has this engine been maintained? What's the max revs it has seen according to the over-rev log on the DME?

[radialaced]

Yes, smooth as silk. The LTW FW and trans mounts don't help, but how well has this engine been maintained? What's the max revs it has seen according to the over-rev log on the DME?

ouu, that's a good question. I didn't know the DME recorded that. It could tell me about money shifting I suppose.

Thanks