Mga Gurus, pa-help naman.
My ride is a 1997 corolla xl. I had it serviced by a shop in cavite for oil leak elimination. However, after that, oil pressure indicator shows up everytime I step on the brake, at pag very slow moving at pag naka-idle. I also had the water pump changed and the engine tuned-up sa ibang shop naman.

Medyo nawala ang nginig ng makina, at medyo lumakas ang hatak niyo, pero me whistling sound na sa engine. Malakas ito pag kai-start lang, at nawawala rin afterwards, pero bumabalik din pag umaandar na pero medyo mas mahina na. Ano kaya ang dahilan nito?