I as an Iranian who remember both pre and post-revolution times can share my understanding as follow;
- Most people have no correct understanding of the reality of Pakistan and its people.
- There used to be a very positive view before revolution, yet not as positive as Iranian view toward Japan, France, Germany, Lebanon, etc.. but among neibours Pakistan was one of the top options...
- During Iran-Iraq war (80-88) Iranians had also a positive view of both the country and its people.
- During Khatami presidency (ending by 2005) Pakistan has its peak of positivism as a country and somehow still positive view for its people.
- In last decade few negative phenomena started to affect this positive perception in Iran.
First, Pakistani national beggars became a visible scene in Iranian streets. I personally encountered tens of them begging for money in streets under fake excuses. There scene is no longer tangible in Iranian cities due to the action by the gov and awareness of Iranian citizens. This phenomenon seriously harmed Iranian view toward Pakistani brothers and sisters. There is another scene that is working against them. In Mashhad, if you go to Bus Terminals or cheap inns, you often see a large group of Pakistani religious tourists sitting (sleeping) on the dirty ground in a not so sanitary way. I have witnessed some personally. The scene is like you see 50 to 100 Pakistani male and females and children sitting on the hard ground or asphalt in a big human mass and they threw visible trash around them in a visible circle. This is not a good scene and I always was angry with their tour managers to not think about the image. I,m sure all of those people were nice and good people but every mass activity needs some rules and managers to handle it nicely.
Second, recent Pakistani political and religious backup of Saudi Takfiri agenda that is obviously an anti-Iran movement made so many Iranians hurt. They thought like Pakistanis are much much more closer to Iranians than Saudis, culturally, religiously, history, etc... But Iranians think Pakistanis are not independent enough to decide for themselves. This is what the majority thinks..
Today, the general view is that Pakistan is a poor developing country that despite its huge 200 million population is not independent and always listen to others for its decisions. Iranians became sure that Pakistan even though they have atom bombs are not strong enough to have even one gas pipe line for their own people needs and are always listening to the ones who bribe them with money or threatens them with power.
Most Iranians consider this Iran-India relation excuse of some Pakistanis as a very fake excuse as most of Pakistani's more firmer allies have far more strategic relations with India than Iran ever had.
Despite all these that I mentioned, if you ask an average old man or woman they would say they still have a positive view of Pakistanis. If you ask a young Iranian they would either say, they never thought about it or care enough to think about it or will try to be polite and say "we are neighbors"..
A few month back I had a Pakistani family friend came to me directly from, Islam Abad and I was a host to them. I took their young guy and girl to the average people and to markets and we interacted with normal people. Most people reacted as if they are Indians working in Iran. When I said they are Pakistanis they were surprised. but the overall reaction was still positive and friendly.
btw, I,m saying all this but you have to know that a considerable number of Iranians are racist people even without knowing it... If you ask them they would say "No, we are not racists" but then their actions shows how they are racist. This is a very bad problem and thanks God, it is diminishing among young generation.
overall, I think Iranians will become more positive toward Pakistanis in future. The more we hear about Pakistani becoming advanced scientifically and technologically and the more we see decent Pakistanis in Iran the more we get positive about them.
Religiously, Iranians consider Pakistanis to be very pure and sensitive. I found out recently that even Paksitani Shias who visit Iran for religious reasons are so so so much traditional and firm on their culture and beliefs. This is both good and bad at the same time. but one thing I am sure by now is that Pakistanis are very kind and pure people in heart and can become good friends for life.