Mysterious vibration around the 2,000 RPM range

Buddy · 6 May 2015

Guys,

I have a 1996 automatic transmission.

Car runs great. But when the RPMs are in the 1,800 - 2,300 range, the car experiences a substantial vibration. At idle, it's smooth as silk, as it revs up towards 2,000 it begins to vibrate to the point that it can be felt in through the steering wheel. This vibration gets stronger as the rpms increase to 2,000, then begin to decrease as it passes the 2,300 mark. Once I'm over 2,300, it goes away, and the car once again runs like an NSX is supposed to.

I've had three highly experienced NSX mechanics, check it out, and no one has been able to find a solution.

Even Ferman Acura in Tampa is shaking their heads.

Please, any help would be appreciated.

The vibration also occurs with the car sitting on level ground in neutral.

It almost feels like it could be a transmission shudder caused by the tourque converter, except I'm told that it would not happen in neutral if it was the TC.

austrian type-R · 6 May 2015

A costumer of mine had a similar problem. We have seen the vibration on the rear wing at low rpms.....we tried different things like ignition cols frm another car, checke dspark plugs and connectors. We ended up cleaning all injectors and it was gone away. Ship your injectors to RC, they clean them and they are like new after the service.

Speedmaster · 7 May 2015

I currently have this issue. My NSX tech cannot quite figure it out either. I replaced the injectors with RC Engineering cleaned ones. I changed the plugs, adjusted the valves. I cleaned the throttle body. I think that since my ECU is throwing the O2 sendor code, I will replace them and see if that helps.

Odd thing, after driving for two hours at interstate speed (70 ish) the vibration goes away (like after I stop to buy fuel or get a donut and take off again, hitting that rpm range.)

nis350 · 10 May 2015

This is normal....

Buddy said:
Guys,

I have a 1996 automatic transmission.

Car runs great. But when the RPMs are in the 1,800 - 2,300 range, the car experiences a substantial vibration. At idle, it's smooth as silk, as it revs up towards 2,000 it begins to vibrate to the point that it can be felt in through the steering wheel. This vibration gets stronger as the rpms increase to 2,000, then begin to decrease as it passes the 2,300 mark. Once I'm over 2,300, it goes away, and the car once again runs like an NSX is supposed to.

I've had three highly experienced NSX mechanics, check it out, and no one has been able to find a solution.

Even Ferman Acura in Tampa is shaking their heads.

Please, any help would be appreciated.

The vibration also occurs with the car sitting on level ground in neutral.

It almost feels like it could be a transmission shudder caused by the tourque converter, except I'm told that it would not happen in neutral if it was the TC.

Speedmaster · 22 May 2015

O2 Sensors replaced.

Vibration still there. (No surprise.)

I am beginning to think it is mechanical (i.e. clutch).

solidol · 23 May 2015

Speedmaster said:
O2 Sensors replaced.

Vibration still there. (No surprise.)

I am beginning to think it is mechanical (i.e. clutch).

Does it go away or becomes less noticeable after you warm up clutch? Sprinted drive shifting at higher rpms.

Speedmaster · 23 May 2015

solidol said:
Does it go away or becomes less noticeable after you warm up clutch? Sprinted drive shifting at higher rpms.

It seems as though it does go away after I have been driving for a decent amount of time (60"+)

What are you suggesting?

solidol · 23 May 2015

Speedmaster said:
It seems as though it does go away after I have been driving for a decent amount of time (60"+)

What are you suggesting?

Some chatter when cold and contribute to slight vibration. Goes away when warmed up. Like few hours of driving. I've seen it happen and my single disc definitely behaves like this.

What clutch do you have? Have you checked engine mounts? Does it happen with steady throttle applied or when on and off it? If you go to neutral does it still vibrate?

Speedmaster · 23 May 2015

Happens in neutral, I don't feel it at all when in gear and accelerating.

My original thought was that I had a misfire or stutter of some sort. Three NSX techs (one of which is very well-known here on Prime) at different times have seen it in person and are unconcerned about it. (As an aside, as I travel for work, I like to bring my car to different NSX techs to get their feedback on the car when they do their reviews, etc. I bring parts with me like O2 sensors and have them do a job and then ask for any commentary/feedback on what they see.)

To be clear, it is an ultra-light vibration, happens between say 1800-2100 rpms, while in neutral. To me, it feels like a mechanical mis-balance somewhere. My sense is that it is clutch-related since I know I will need one in the next 10K miles.

chussey · 23 May 2015

"In the V6 with 90° between cylinders, split crank pins are required to offset the connecting rods by 30° to achieve an even 120° between firing intervals, and crankshaft counterweights are required to offset the primary imbalances. In the 90° V6, a balancing shaft is desirable but not entirely necessary to minimize second-order vibrations, depending on the level of smoothness required."

"Therefore, designing a smooth V6 engine is a much more complicated problem than the straight-6, flat-6, and V8 layouts. Although the use of offset crankpins, counterweights, and flying arms has reduced the problem to a minor second-order vibration in modern designs, all V6s can benefit from the addition of auxiliary balance shafts to make them completely smooth."

There is a reason Honda added a balance shaft to the later 3.5 C series V6.
Our engine mounts that are potentially up to 25 years old do not help the situation either.

solidol · 24 May 2015

Speedmaster said:
Happens in neutral, I don't feel it at all when in gear and accelerating.

My original thought was that I had a misfire or stutter of some sort. Three NSX techs (one of which is very well-known here on Prime) at different times have seen it in person and are unconcerned about it. (As an aside, as I travel for work, I like to bring my car to different NSX techs to get their feedback on the car when they do their reviews, etc. I bring parts with me like O2 sensors and have them do a job and then ask for any commentary/feedback on what they see.)

To be clear, it is an ultra-light vibration, happens between say 1800-2100 rpms, while in neutral. To me, it feels like a mechanical mis-balance somewhere. My sense is that it is clutch-related since I know I will need one in the next 10K miles.

C30A is not very smooth in that rpm range. I've noticed this since day one. I just got rebuilt front/rear engine mounts and very curious if stiffer insert will transfer more of this vibration to the chassis but it also should help minimize unbalanced state when engine rocks back and forth under acceleration/deceleration.

When you're in N clutch released or not?

Speedmaster · 24 May 2015

Yeah, no change with clutch in or out.

Andy swung by today and didn't even notice it when I had him rev the motor. I might be a tad "particular" on this one. After all, it is not BMW 6 cylinder (smooth).

We can close this one down. If NSX techs tell me not to worry and you do as well, I am moving on.

s14_tat · 26 May 2015

The vibration is normal. A few years back i drove a 2002 with under 30k miles on it just to see if his had this vibration and it did.

Mysterious vibration around the 2,000 RPM range

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