TROUBLE: 2002 ZX3 Zetec IAC goes to 65% after throttle blip then drops slowly

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Seattle
State
WA
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United States
What I Drive
ZX3
#1
Thanks for reading this. I'm using a Launch X431V for diagnostics and it shows that I have no engine DTC codes (P1000 only after KAM reset).

Symptoms: With the engine fully warmed up, after I blip the throttle, the PCM indicates that it has a "desired rpm" of 704, but sets the IAC to 65% which launches the engine speed skyward to ~4500 rpm. When I attempt to drive the car, the PCM sets the IAC to ~60% and the car will essentially drive and accelerate (manual trans) without any throttle input. Yes, I agree, this is somewhat dangerous and I'd *really* like to resolve it! After a couple of seconds, the PCM gradually drops the IAC back down to 40% and the idle follows the IAC setting precisely.

I have good vacuum off the back of the intake. DPFE sensor and solenoid are working properly. No fuel in the vacuum line from the fuel pressure sensor. EGR works properly (stalls engine when run up). IAC works properly (complete control of idle). TPS works properly (0.95V at idle and responds linearly). I have blasted carb cleaner all over the intake and vacuum lines and not been able to detect a vacuum leak.

I was having idle issues with the idle running up and down and noticed wavering vacuum on the EGR line to the DPFE so I replaced the EGR which resolved that. I replaced the IAC that occasionally clicked while trying to control idle air at about 700 rpm, but PCM seems messed up as it commands IAC high when it should not be! Keep-alive-memory has been reset. No DTC trouble codes. Engine drive cycle has *not* run. The EGR tube is the updated design with the heat-shield on it. It does not collapse when the revs are run up. PCV is recently new and works perfectly. Valve cover gasket (replaced about a year ago) appears to be seeping oil a little at the front cover, but not filling the spark plug holes. I cleaned the MAF with MAF cleaner (without touching the wires) and it made no difference.

Recently resolved problems:
Replaced alternator about 6 months ago
Thermostat housing cracked, leaked coolant and the engine overheated a bit (did not seize and is not knocking, not losing coolant). The coolant distribution tube above the radiator also split apart and was replaced at the same time. Engine is not loosing coolant and builds pressure.

Known issues thought to be unrelated:
Power Steering Pump sensor throws a code after performing a KOER self-test. It's also a bit noisy. I have a seal kit for it, but I've been throwing my time at trying to resolve this IAC control issue.
Historically, the long term fuel trim sits at about +5% since I bought the car at 105k - it's at about 140k now. I haven't had any driveability issues with it. until recently when it started occasionally stalling at a stop. This became worse over time so I started investigating, which led me to find the clicking IAC, etc.

Any diagnostic advice with procedures for checking suspected failure points would be most appreciated. Or, if anyone knows the inputs that the PCM uses to decide how to set the IAC, I could try monitoring them to see why the PCM is controlling the IAC so high.
 
Last edited:
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ala.frosty

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Messages
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City
Seattle
State
WA
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United States
What I Drive
ZX3
Thread Starter #2
I guess I need to look elsewhere for Ford Tech people. :-(
 


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