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i've checked hoses, cleaned ICV..

have been using cheap (cheapo) gas regular (maybe water in gas?)..filled with different brand, seemed to run better

mechanic thinks there may be a leak at intake manifold to cylinder head..that's a big repair..

Rough idle could be caused by a vacuum leak. Under the hood, there is a diagram by the battery. Check all those hoses for cracks and tight fit. Sometimes, cracks would be hiding in hoses' turns/ribs. Chances are very high that it is some small stupid leak somewhere. I will tell you that I've seen a very few m30s with steady idle.