"91 S-10 Failed Emissions - HIGH HC - help???

[davidzog]

My son's 91 2.8L s-10 failed with high Hydrocarbons but had low CO....

The catalytic converter was rusted and noisy, so we had it replaced and I replaced the IAC valve as the idle was goofy, and I also am going to replace the oxygen sensor and EGR valve this weekend.

However, the engine idle recently started surging from 800 to about 1200 rpms (back and forth) and I have no idea where to look...any help on passing emissions and idle surging would sure help a lot...thanks

[maxwedge]

High hc's are usually raw fuel fumes, make sure the oil is freshh, the vapor cannister is not loaded, no misfires. As for the rpm surge, vacuum leaks # one, carb base, possible egr not seating was common, scan it and look for codes and proper sensor operation also.