I'm the original owner of a 1990 CRX-Si 5-speed with 110K miles on it. It is in great shape and only driven during fair weather. I do all the maintenance on it. Recently while driving on the interstate, I am feeling a vibration. If driving at say 75 mph and you start to accelerate, there is a shuddering or vibration felt. It is especially noticeable when accelerating on an incline. If on the level and holding 75 mph, there is no shuddering. It is only when accelerating that the shuddering is felt. The tires are fairly new high-performance and balanced. The shuddering-vibration feels like it is coming from the driveline. I inspect the CV boots every oil change (3K) and there are no tears etc. But I am suspecting it may be CV-joint related. Does anyone have any ideas of what may be causing this? Thanks, Charles

 

Did a little searching in FAQ and came up with this:

https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/faq-axle-replacement-tutorial-pics-382416/

Sounds like it is the CV joints.