1998 Isuzu Trooper smog failed:

At IDLE is where it is failing.
HC (PPM)
Max Ave Measure
100 17 175

at 2500 RPM PASSES
HC (PPM)
Max Ave Measure

170 13 30

Things done to try and fix and have it passed:
Removed and cleaned intake manifolds, EGR lines, NEW EGR, tune up (new plugs)...

No Vacuum leak detected.

One thing that may be causing this is a cut I made at the exhaust (upstream of the catalytic converter) because the starter gave out last year and I replaced it. The starter was on the drivers side front wheel. The only way to gain access to the starter was to remove the exhaust pipe. Unfortunately, I was not even able to loosen the three bolts to remove the exhaust pipe from the manifold and had to cut to the exhaust pipe to gain access to the starter.

I patched it up with the wrap around metal piping and used a high temp gasket maker to seal off any leak. Maybe this is what''s causing the high HC? I am not sure. Last resort would be to have it welded shut.

Can an O2 sensor failure cause high HC as well? maybe even a failing catalytic converter?

Any help is appreciated.

Thanks.