Yes another vibration thread... I know there is a ton of them because I have read every one that I can find... Seems everyone has a different scenario. Just looking for some advice on where to go next with mine.

Ill keep it as concise as possible:

1990 Formula 305 TPI/ 5 Speed all original 74k miles bought it last spring to fix it up wasn't running at the time.

I have been slowly fixing everything on it to make it my weekend cruiser and have everything ship shape.
Have put a bunch of sweat and tears into it (fuel pump, shocks, brakes, ball joints, interior etc) finally down to my last gremlin

Engine vibration at low RPM typically worst at about 2100 RPM and when under load, happens in gear at all speeds, but also in neutral sitting still in the driveway (so eliminates a wheel/suspension/driveshaft issue)
Can see the engine shaking slightly when standing over it and holding revs, but i feel it more in the cabin/seat and shifter when I am in the car.
The engine seems to sound great and pulls strong through the rev range when driving it however

First I replaced the Transmission mount with the nice rubber one from NAPA that has more meat than the cheap ones, the original one was cracked but not falling apart - no change
My clutch was chattering and didn't feel great sometimes so after reading threads I figured both the vibration and chattering could be the clutch and flywheel with hotspots/warping.

Decided to have a shop do the whole clutch kit and replace flywheel - price was reasonable and I had enough of laying on my back in the driveway for the year.

The chattering is gone and the clutch feels great now, so I am happy I did the replacement (there was lots of hot spots) but the vibration is still there and feels about the same.

Motor mounts visually look OK and I can't see any movement at the mount
only other related thing I've replaced is New R45TS spark plugs when I first got it in the spring

Any advice on what else it could be? some type of misfire? timing? (even though it runs great?)

Thanks for reading everyone, any comments are welcome

 

Have a look at the harmonic damper , specifically , look to see if the rubber between the inner hub and the outer ring has deteriorated enough to allow the outer ring to slip and loose it's index with the inner hub .

 

Is the engine missing? Have the injectors been replaced yet? When they get sticky from age, they can cut in/out at different rpm. That'll give you an odd shake.

 

thanks I will take a look at that.. Ive never messed with the harmonic damper on my thirdgens but I will look at some other threads and my service manuals

 

it really doesn’t seem like it’s missing or cutting out at all, the rpms climb smoothly and it pulls hard, I will not rule out injectors yet though thanks for the input. I had bad injectors on my GTA and they behaved much worse

 

Well if you eliminated the flywheel and everything behind it it's now engine related. Remove the fan belts or serpetine belt and check for vibration to rule out the accessories.

If not an accessory then compression and leak down tests will show you a weak cylinder. You should read your sparkplugs at this time also. Could be something simple as a cracked sparkplug.

Finally try pulling one plug wire at a time to see if you can identify which cylinders are good and any that are bad as running on six cylinders should be worse than seven.

Good luck and hope this can help.

 

Thanks! I will be looking at the harmonic balancer/ belt accessories and plugs and go from there

 

Just for anyone's future reference, new injectors did solve the problem! they must have been gummed up from when the fuel pump went bad and there was bad gas in the tank when I bought it (the rubber pump ring was all melted as well). I put a set of bosch d3's from southbay in and she is running great now.