My 1989 Accord Lxi runs well, but when it's in neutral or park, the idle speed goes back and forth from about 1k to 2k at a frequency of about 1 Hz. The dealer cleaned the O2 sensor and that fixed the problem briefly (at least till I drove out of the shop and down the street). Any ideas what may be the problem? And given that it doesn't seem to affect performance, is there any reason to fix it? Thanks Steve