We don't know because A) we rarely see an average Vulcan, B) IQ tests are a poor measure of intelligence and C) "intelligence" is ill-defined.
How do you measure intelligence? The OP mentions IQ, and IQ is thrown around in Star Trek a lot. It's possible in the future they've developed a definitive definition of intelligence and a reliable IQ test, but I doubt it. They're still struggling with sentience. Lacking any evidence, I'm going to use the modern ideas of intelligence and IQ.
There are a variety of different IQ tests which attempt to measure "intelligence", but they're all widely acknowledged to be biased. It's not known if IQ is measuring intelligence or a person's social and economic standing. Given that IQ tests are controversial in humans, they're probably going to work even worse on aliens.
And then there's the matter of the IQ score. Star Trek loves to throw around absurdly high IQ scores like 1200 for super-Barclay or 2005 for Q. These are nonsense. Your IQ score is based on your raw test score, but it doesn't scale linearly. An IQ score of 2005 means Q had a raw test score of something like 10,000 on a test where you're supposed to get raw scores of 20-500. How does that work? Does everyone but Q get most of the test wrong? Did Starfleet make an IQ test scaled to Q's intellect? Likely the Q have their own completely unbiased test for themselves, or Q just made it up on the spot to try and impress (not so) gullible humans.
But I digress.
What about the Vulcans we do see? Let's look at Spock (in TOS), T'Pol and Tuvok.
Spock and T'Pol show extraordinarily high deductive, analytical and mathematical skills. Spock, in particular, is able to perform astonishing math equations in his head. However, they both show extraordinarily low emotional intelligence, particularly with regard to humans. They're so bad at it they often choose to belittle it or simply ignore it leading to some very poor decisions. This could be a product of trying to understand humans, but other races don't seem to have that problem.
Spock and T'Pol are both scientists, either graduates of the Vulcan science academy or worked with the science council. Both show signs of indoctrination. Spock, despite his years among humans, continues to ignore their emotions. T'Pol hates emotions (yes, hates) and has an even lower view of humanity than Spock, but goes even further by letting her biases cloud her scientific judgement by denying observations which contradict Vulcan scientific doctrine (ie. time travel).
In contrast, Tuvok is not a scientist. He is a graduate of Starfleet Academy and later taught archery. While he finds human behavior often curious, he rarely demonstrates the same frustration or derision that Spock and T'Pol do (or only to get a rise out of Paris). In fact, he seems to have figured out humans (and everyone else on Voyager) so well he can practically predict their actions. This serves him as security officer very well.
In short: "Intelligence" is very slippery, many factored thing that cannot be measured with a single number. Someone can be very tuned into certain factors, but totally blind to others. This combination, coupled with arrogance in their own thinking, can give them some very poor judgement. I think most Vulcans are well rounded, but the Vulcan Science Academy turns them into awkward, arrogant, bigoted science nerds indoctrinated in the superiority of Vulcan logic.
Fortunately, Spock gets better as he gets older.