Hi all, i have been chasing a high idle problem since i bought my indy a year and a half ago, i have replaced or fixed just about everything on it, which did fix the worst of the high idle, but it still idles around 1400 rpm, today i was looking around my engine compartment and noticed a hairline crack on my exhaust manifold, just above the 02 sensor(at the weld joint), could this be the cause?? If so is the a way to fix it without replacing the manifold?..thanks..jim(2 '84 Indys)

Yes it can cause problems if it's letting air into the O2 sensor. There is no reliable permanent fix but to replace the manifold.