Engine misses at low idle

I have a 1992 Honda Accord LX with 175,000 miles. I have replaced the cap, rotor, plugs, wires, oxygen sensor, fuel filter, and air filter to name a few. The car still misses at low idle. I can't afford to replace everything, and two shops that I have taken it to have not been able to figure out why it runs great at higher rpms, but misses at low rpms and idle. At stop lights if you put the car in neutral it stops missing. No codes come up on the dash. My guess is that it is probably a vaccuum leak. But do not know for sure. Any help would be greatly appreciated.