Why my signals surge when I increase the nebulizer gas?

We infused 1ppm caffeine to MTQ with standard spray condition for infusion. The signal disappears slowly when initially sprayed to the system. Nothing we do will improve the signal, until we increase nebulizer gas pressure from 0.5 to 1.0 then 2, and 3 bars. Each time signal surged and then drop. Later we found that it was because the syringe pump was not working. The surge of signal was due to the nebulizer gas drawing the same from the spray needle.