So here goes, I've been reading / searching etc. for the past 2 months, so bear with me.

The Car:
1998 Civic Si (canadian edition) 5spd, No A/C, 170k km / 110k miles. Stock everything.

The Problem:
When cold ---> the car is generally fine, quick starts and no real issues to speak of.
When warmed up
- Fluctuating idle when stopped, almost to the point of stalling
- At speed, when applying light throttle, car will drive normally. Revving freely up to 6k+.
- At speed, when applying a reasonable amount of throttle, the car will "stutter" or hesitate. If you stay into the throttle, the car will shudder more and throw a P300,301,302 & P1399 code.

What I've done
- Replaced spark plugs (twice, with factory NGK & bosch)
- Replaced ignition wires (NGK blues)
- Replaced cap & rotor
- Swapped distributor and resistance checked 3 sensors (all are ~350 ohms)
- Replaced ignition coil
- Replaced PCV valve
- Cleaned throttle body
- Replace air, oil and fuel filter.
- Checked for intake/ vaccuum leaks
- Adjusted / Calibrated TPS sensor
- Cleaned IACV
- Cursed the thing and contemplated rolling it into a lake...


I'm starting to think my cat might be plugged up, does anybody see something I'm missing?

Any help would be greatly appreciated!

-Adam

 

I'd check your MAP sensor, get one from a junkyard, auto stores usually charge around 80 for one.

 

check the timing

 

Check your primary O2 sensor as well. Mine had a hesitation/stumble and it was just a wasted O2 sensor. Mine never threw a code though.....Replaced it and it made a WORLD of difference. I even picked up like 3mpg...

 

Should have mentioned it,

I had changed the O2 sensor and it had no effect.

-Adam

 

Try cleaning your IACV as well.

Also, are there NGK plugs in now? Check the gap.

 

might be the cat as well..

 

Cleaned the IACV, adjusted the TPS within spec. No change, problem persists.

Map sensor looked clean and tested fine.
Plugs have been gapped.

-Adam