INTPs are more logical, but INTJs are more efficient.
Also, it is theoretically possible for INTJs to be more motivated by emotion...in fact, this is probably more true of them than INFJs. This is due to the INTJ's tertiary Fi, which means they could have a stronger sense of internal values.
When not extroverting, the INTJ uses Ni and Fi, which could combine to form an idea subconsciously motivated by passion, which is then expressed forcefully via Te, without regard to established norms.
The INFJ, by contrast, uses Ni and Ti, so they are more motivated by imagination like the INTJ, but their tertiary function is motivated by pure reason and logic. When these introverted functions work together, we get the stereotype of the INFJ being a psychic prophet, or the paranoid person whose conspiracies are right...it's the axis of Ni's imagination and Ti's penchant for logical skepticism.
When functioning internally, the INTP uses Ti and Si, and this is how they represent the "walking encyclopedia" stereotype or a person who is interested in learning for the sake of learning. Ti analyzes the logical fluency of Si's internal forms. When engaging their Ne, the INTP has a knack for gaining a new way of logically seeing reasons behind things.
The ISTP, using Ti and Ni internally, is probably the source of this type's tendency to be rebellious. When engaging Se externally, the ISTP is able to use these functions for troubleshooting. This type is also stereotypically a keen observer of subtle changes in the environment. And since Se alone is focused on pure enjoyment of physical impulses, the function is modified for the ISTP and is thus more graceful and conscientious of them -- they are less reckless in expression of physical impulses. They use Ti to satisfy Se, and Ni serves this type's improvisational skills. I have observed, too, that many ISTPs are indeed interested in martial arts, individual sports, mechanics, working with tools, etc., and at the core, the ISTP, like the INTP cousin, is into science and mathematical theory, but the difference is that the ISTP will use the theory for more applied purposes (troubleshooting, observation, labwork, and so forth), while the INTP will use it to dream up something new with their auxiliary Ne.
So the INTJ and ISTP are more similar in that they are more concerned with usefulness. But the INTJ is more useful in that he uses the external world for purposes of fulfilling a vision, while the ISTP uses the internal world as a means for planning the next physical move. Now the INTJ also has Se as an inferior function, but since it is so undeveloped, the INTJ could merely fantasize about the physical responses to make by imagining various scenarios -- a famous example of an INTJ is, therefore, Travis Bickle in the film Taxi Driver -- the ISTP is more about analyzing opportunities for the next move.