I have an '86 Sammy, with 30K miles on it. Recently, it has begun to run REALLY badly after warmup. This symptom will come and go, but it now is mostly here to stay. After W/U (and now, even when cold) this pup acts like spark advance isn't working (it is)... it won't GO. I can hear exhaust escape from somewhere under load (above 2000 rpm or so) like it's leaking past a gasket. Here are the things I noticed:
The catalytic recently started intermittently rattling (but the heat shield seems okay). When the rattle is gone, this problem seems to be worse.
When the symptom appears, the exhaust tube from the EGR (not the vacuum fitting tube) valve blows off the modulator assembly (indicative of very high exhaust pressure?)
Sound like an obstruction to you? In the cat? The odd thing is that this problem can vanish for days or weeks.
I yanked the O2 sensor today and the beast runs well. The modulator hose did NOT blow off.
If you all agree that I should deal with the exhaust, what would you recommend? I live in California, so I need to keep the cat. I'd like to put up a set of headers, a new cat and a reasonably quiet muffler. Suggestions and sources? What kind of cat? What should this cost?