OTSir, it is a two-way traffic. In early to mid-90s there was a lot of sectarian violence with equal support provided by Iran. Low-key sectarian violence is still taking place, and Iranian-supported groups are on the losing end, generally.
Iranians have been recruiting volunteers from Parachinar (adjoining Afghanistan) to fight in Syria. However, I will concede that in the past years monetary support from GCC has emboldened some groups to support violence inside Iran. But then it is not purely a matter of terrorism as such, since Iranian Mullahs suppress Sunnis who predominate in certain areas such as Sistan (Baloch areas under Iranian control). Balochistan is sparsely populated and poorly governed and Pakistan find it difficult to secure the border and cut cross-border movement.
There are other issues such as Iranian tacit support for Indian-sponsored subversion inside Pakistan, Crime bosses from Karachi traveling on Iranian passports, generally hostile Iranian policies on International fora, etc...
In this context, one can place the latest incident of JF-17 being used to kill the Iranian drone deep inside Pakistan's air-space. If Iranians had wanted a partner in peace, there would have been a positive engagement from Pakistan, since Pakistanis generally view Iran favorably. From the Iranian side, though it seems to be a different story.
Iran has no interest in conflict with Pakistan. The threats from US and KSA are enough. Think also of the wars in Iraq and Syria.
There is of course suspicion of Baluchi's in Sistan because some of them are subverted by the Armed Non Governmental Organisations from Pakistan but Iran does not in general suppress Sunni's , Christians or Jews. The country that is interested in subverting Pakistan is India. And there are of course factions in Afghanistan.
Iran is an industrial nation and Pakistan is beginning to grow into an industrial nation fast because of Chinese support so trade between Iran and Pakistan promises to become important. That is more important to Iran than a possible wish to subvert Pakistan: What would be the purpose?