Problem with 09 Vios 1.5G idling

[JunDC]

Good day. I recently bought a 2009 toyota vios 1.5G a/t. On the day i bought it, i drove it 40kms from the seller to my place, walang problema. Then i used it that same day to go around town. The following morning, i was supposed to move it sa garage para ma detail. When i started the engine, the tachometer went up and down, ranging from 1500-3000 rpm. It has been going on like this for a month now. Minsan pag natanggal negative terminal, yung idling bumabalik sa normal(steady at around 750rpm). Usually, the problem arises kapag cold start. No check engine light. Just irregular idling, parang binobomba yung gas pedal. Meron na po bang naka experience neto? Or do you have any idea what the cause is? Throttle is clean, dinala ko na sa dalawang trusted mechanics ko pero persistent yung problem. I hope you could give me some inputs regarding this. Thanks in advance.

[dhenz76]

sir pa check mo po IAC, pwede rin po meron isa sa coil pack ang sablay na. linisin mo na rin MAF sensor at check vacuum hose leaks