My beautiful yellow 1991 2+2 NT (129,000+ miles, had since new) has been at the local Nissan dealer service center for weeks. After they put in dye (for the second time) to trace an AC leak (cost me $$$ for new compressor), engine started running rough intermittently. They cannot seem to diagnose it as it is "old technology". Any ideas on the problem (I think they dislodged as hose, cracked a wire, etc), and/or how they can diagnose it as it is intermittent? It happened from something they did, but of course they are saying NOT.