Went to dealer to test why my 2000 Mustang GT had a jumpy idol no check engine light was on he said it was the IAC so bought a new new put it on and still does it. Do u guys think it is the TPS and for a 2000 u cant adjust it right u have to get a new one and by the way the mass air is clean. Someone said the reading was coming back IAC was bad is because of the TPS could tis be true.

If for some reason the TPS voltage is off, that could cause a bad idle and hesitation. I usually go for .95-1.00.

is that what it sounds like

Could be. It wouldn't hurt to check it though.

Your best bet would be to check the TPS voltage. I have this article which should get you started, but the wire colors may be different as that article is aimed toward 87-95 cars.

Too bad you bought a new IAC valve there is an article on this site about cleaning it, plus other ideas on rough idle. I just bought a hypertech flash/programer mostly because I changed my rear end gears, but it picked up on OBD II codes and I had no check engine light. Have you put a new PCV valve in? I was skimming through trouble shooting in the Haines manual and I'm pretty sure it mentioned the PCV valve, I don't have it with me now but I will loo it up and let you know.

Too bad you bought a new IAC valve there is an article on this site about cleaning it, plus other ideas on rough idle. I just bought a hypertech flash/programer mostly because I changed my rear end gears, but it picked up on OBD II codes and I had no check engine light. Have you put a new PCV valve in? I was skimming through trouble shooting in the Haines manual and I'm pretty sure it mentioned the PCV valve, I don't have it with me now but I will loo it up and let you know.

Sorry about the double post I'm just learning this site. I did however check about the PCV valve affecting idle RPM. To ceck the valve just remove it with the hose still hooked up, start engine and put your thumb on engine side of valve, you should feel a suction of some type. If not remove the valve and put your thumb over the hose and feel for suction. If no suction is felt find the obstruction.