First of all, I really did try to search, but the search function has been disabled . WTF
Anyway, a week and a half ago I had my car running for the first time in a while. The harness was fucked so I had to tear the intake off and redo the harness. When I got everything back together, it had a really bad vibration that started at 5k RPM and kept going. It did this in all gears (except 5th which I couldn't test at those speeds) and while revving in neutral. When I got it running the first time it was not doing this. The engine was perfectly smooth all the way up to 7k (the highest I took it.)
Its pretty bad and I'm worried it could damage something like it is. What would cause a vibration to suddenly start like this?

 

Mine has a similar vibration. I have new engine and tranny mounts, yet it still vibrates. Mine does it a bit when in neatral and revving, but mostly under load running hard on the interstate. Makes me nervous to go over 5,000rpm, scared **** will fly apart

 

Well mine does it just about as bad regardless of whether its in neutral or what gear its in. The things that I can't figure out is why it would suddenly start doing this when I didn't change anything. All I did was put in new plugs and wires. I'll have to do some more tests tomorrow I isolate exactly how its behaving.

 

Only thing on my car that I havent tried changing is plug wires. they are pretty old, but now that I think about it, I guess they could be worn out to the point that they arent delivering voltage at high rpm's and causing it to run very rough... maybe. Otherwise i have no idea. I have a new clutch, flywheel, counterweight, pilot bearing and seal, trans mounts, engine mounts... what the hell else would cause such a violent vibration

 

Put the correct counterweight on?

 

Yes. Now that I think about it, mine sort of seems like there is a certain rpm it does this. Its not a gradual increase in vibration, it just suddenly starts at a certain rpm. Is yours like that Sideways?

 

I am in the same boat. I found that occationally should my car flood, it'd solve the vibrations for the next hour or till I turn the car off. I am checking my plugs tomorrow and checking the fuses.

 

My TII seems to vibrate small amounts at almost all speeds and rpm's. Might be missfiring throwing the rotor off its oblong path a little. That's my best guess.

 

its probably lack of spark. sort of like the rev limiter (not sure if its fuel or spark cut) at high rpm's the plugs areneeding to fire faster than the ignition system can supply, wether it be plugs, wires, or something else. This is all I can figure. Like I said, mine mostly does it at high rpm. Very slight atl ess than 5k but over 5,000rpm-5,500rpm, it gets really bad all the way to redline. Its slowely shaking my cars interior panels loose.

 

I had the exact same problem. It was my stock fan clutch not releasing. If you still have it try changing it with another and see if the vibration goes away.

 

Thats a great idea, Umi. I'll have to check that out.
And yes, FCKing, thats almost exactly what its like. At 5k it gets worse to 5.5k where its really bad all the way up.

The thing I forgot to say earlier is that its really just my gearshift that is vibrating. I can't feal it in the seat or steering wheel but the gearshift feels like a powerful massager.

 

I've had the same problem for a long time now on my 88 GTU and I've never really figured it out. It makes my whole interior resonate... lot of rattling practice. It seems to be correlated with the exhaust--it depends on the frequency basically. I haven't been able to figure it out.

Strangely, it really showed up when I switched from catback from Apexi N1 duals to RB. Weird... like I remember I had to take it to the muffler shop and when I drove it after that I noticed the shifter and the whole interior vibrating a ton. Yet the car itself is a lot quieter. When I pop the hood while the car is idling I can see the engine vibrating.

 

Mines pretty much the same. I still have a slight vibration throughout the car, but mostly in the gearshift. Makes my hand hurt it vibrates so hard. I might just take my fan assembly off and drive it real quick and see if that does anything

 

Yeah, it really does almost make my hand hurt. It reminds me of when I hit a tree stump with my lawn mower and it got out of balance.
As for removing the fa, I think I might try that too once I get the time. I think I might also be missing a nut on the fan clutch, but I don't know why that would make it suddenly start vibrating. Once I get home I'm gonna do some further testing.

 

let us know.. i have a similar problem.. i can see the engine shake at idle that smooths under load (for the most part) when i manually press the throttle with the car parked in neutral. But when driving its much like the rest state, the gearshift is like a hand massage, ive just had the alignment done and that hasnt solved the shake so im fresh outta ideas

 

Well, for some reason it has somewhat cleared up. I noticed that when I was revving in neutral, the vibrations were worse when I was on the gas than when I let up. I decided to test this while in 2nd gear and after me messing around a bit, the vibrations had mostly gone away. I drove around some more and it has stayed that way. There is still some vibration and I can still hear it vibrating something, but it is far less. It is now to the point where I'm not scared something is going to break, its just a mild annoyance. Sometimes it seems to clear up some more past 6.5-7k, but I can't be sure yet.
There is one possible thing I thought of today. First of all, my car has been idling at 3k. I have the thermowax on but not connected to the idle is higher than normal. For some reason the fast idle cam is jacking the idle WAY up, much more than in the past. When I took it off the cam and back to normal, it started bouncing due to a vac leak. When it bounces there is a metallic "hammering" for a sec at the low end of the bounce as the engine vibrates. I think this might be because a motor mount isn't all the way tightened down or something, which could partially account for the vibrations. I plan on checking into that on Friday.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/pulley-swap-alt-upgrade-getting-high-rpm-vibration-638776/
had a similar problem after switching to serpentine pulleys, vibration at around 5k
up to about 6k rpm. Turned out to be clutch fan for me.

 

Wait, so what did you do to make it go away? Fan clutch?

 

No, it just isn't quite as bad. Trust me, its still there, and it might just be in my head that its better, but it seems like it isn't as bad.
What I have determined is that my fan clutch is bad, as in not working enough. I found this out when I went into town today and my temps started rising. It got up to 195 or so before I could get moving again and bring the temps down. so I think that rules out the fan clutch sticking. That or its just tempermental, who knows, because I could have sworn it seemed like it was too stiff when I first put it on. I still have to test out some stuff, but I'm gonna be busy tomorrow so I dunno how much I can do. Once the car cools down I'm gonna check the tightness of the motor mounts just to be sure.