I recently bought an 89 Si Hatchback for parts. I got the 24 hour permit, and I was driving it around. It seems pretty solid... until later that night. Whenever I would put the car in gear, I had to really ride the clutch so that it wouldn't bog down, and die. Even on the highway, with the car in 5th gear, it would start to die. RPMs would decrease, almost like the throttle was closing. Before I go tearing things apart, what is a common problem to these symptoms? I didn't get a chance to check the ECU for codes, as I was leaving early the next morning. Could this be a mechanical problem, or could it be the o2 sensor?

 

Sounds like you are saying that it idles great, but whenever you put it in gear and drive then it bogs down and wants to die?

Is it throwing a check engine light/codes should be your first check

Could be a clogged fuel filter, failing fuel pump, etc. Bogging only while in gear suggests to me that the engine isn't holding up under load. Could also be a mechanical problem like the tranny binding up.
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^ WHat he said,and DEF chk codez...

 

mind kind of does the same but it idles okay but very low like 500 little bit less then when i push in the clutch it wants to die. it haves check engine light on but i dont really know how to read them ...

 

You can find more in the FAQ
Here's a few to get you started

https://honda-tech.com/zerothread?id=468260
https://honda-tech.com/zerothread/1710584
http://www.c-speedracing.com/faq/06.php

 

handbrake on? frozen brake pad?

 

It is funny though, on the highway when it was almost dying, I put it in neutral and turned it off for a few seconds, then I turned it back on, and it didn't try dying for a while.

 

get your codes and post them up on here!
Thinking you probably got a MAP sensor code.