High idle - P1506

[biederboat]

This is the latest in a continuing saga of trying to get my 2000 ZTS (DOHC) ready to sell. Started with bad timing belt. Let it sit for a few months, replaced it. Battery and fuel pump bad, replaced them. Now a high idle w/ a P1506. So I'm thinking with all the engine jacking up/down to replace the belt must have pulled a hose loose. I've looked pretty thoroughly and can't find/hear anything. Throttle/cruise cables are fine. Idle speed varies, I think it's mostly around 2K.

Is it likely the IAC has gone bad just from sitting? I can't see how the gasket would just start leaking in that amount of time.

Any suggestions greatly appreciated, would like to get this sold as a well running rig as it's in otherwise fine shape.

Thanks,
BB

[Sponsor]

[VillageT]

Look at the large vacuum hose that runs from the IAC to the PC Valve. They split underneath where it is very difficult to see. This is a very common Ztec problem.

[biederboat]

Thanks, I'll check that one out. If that doesn't work out, am I supposed to disconnect the IAC connector while it's warm and running? If the idle doesn't change then the IAC is likely not the problem, is that correct?

BB

[BC_ZX3]

Originally Posted by VillageT

Look at the large vacuum hose that runs from the IAC to the PC Valve.

No such hose. PCV line runs to the intake manifold. IACV uses a separate passageway within the intake manifold.

As a first step, check the IACV electrical connector and wiring is not damaged and is indeed connected. If it checks out OK, disconnect it after the car has warmed up and then been turned off. After restarting the car, no improvement in idling indicates the valve is stuck or unresponsive.

P1506 - Idle Air Control (IAC) Overspeed Error
This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm.
Causes:
IAC circuit short to GND
Damaged IAC valve
IAC valve stuck open
Vacuum leaks
Failed EVAP system
Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.