Finally understood the scene after Jimmy scopes out Pollos.

After the scene where Jimmy is fishing for his watch in the bin, he has a small interaction with Gus. After this scene theres a shot of Gus just cleaning the parking lot and he stops and just starts looking menacingly into nothing. I always found this scene weird. I thought it was just to add atmosphere of introducing Gus again to BCS.

Well I figured it out. At this point we knew Gus found Jimmy suspicous, as the bag Jimmy was looking at never gets picked up. Gus went to clean the parking lot, but to actually see where Jimmy was going. He sees Mikes car and starts thinking, hence the menacing shot.

Mike was already being surveillanced through the gas cap. Gus checks the GPS and now sees the emitter didn't show Mike at Pollos, although he was there. Gus knows Mike knows about the gas cap and figured out Mike was tracking the bag through the old gas cap. All this must have gone through Gus' mind in that standing menacingly shot. Shortly after they confront Mike on the road with the gas cap and cell phone.

Sorry if other people noticed this or it was easy for others. I watched BCS 5+ times now and finally made the connection through the 2 scenes.