I had a similar issue and it turned out to be two issues, bad injectors and one bad coil. Injectors in 90-92 are a big problem over here caused by Ethenol added to our fuel. Are they adding Ethonol over there? If so might be time for injectors. Any type of alcolhol will destroy your injectors. I replaced with FIC injectors. Here is a good read:
http://zr1specialist.com/HAT%20Web/a...eplacement.pdf