1992 Grand Caravan 3.3 High Idle Diagnostics help

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dybber - 25 Feb 2005 03:20 GMT

Hello,
On my 92 Grand Caravan 3.3 I have a high idle (2000 rpms in Park)
problem that
consistently trips the Code 25 (IAC circuitry). Here is what I have
checked
and replaced.
Idle Air Conntrol Motor
No known vacuum leaks or other gasket leaks
No other codes found
The code 25 immediately sets itself even after I disconnect the battery for
an extended period. I even disconnected the PCM and reconnected.
It will show the code before I ever start the vehicle again. It must
set itself
when key is in on position and checks voltage.
When I start the vehicle and backprobe the IAC connector(4 wires) with a
voltmeter I believe I should get a 'cycling voltage' from under 1 volt
to > 12 volts
on each wire. I get these voltages on all the wires except the
black/yellow one.
I traced the wire back through the harness and to the PCM and everything
looks OK.
Resistance tests appear normal. For those who know a ton more than me:
What would be your next steps if you were in my shoes? Thanks

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Comboverfish - 25 Feb 2005 07:23 GMT

> Hello,
> On my 92 Grand Caravan 3.3 I have a high idle (2000 rpms in Park)
> problem that
> consistently trips the Code 25 (IAC circuitry). Here is what I have

> checked
> and replaced.
[quoted text clipped - 4 lines]
> an extended period. I even disconnected the PCM and reconnected.
> It will show the code before I ever start the vehicle again. It must

> set itself
> when key is in on position and checks voltage.
[quoted text clipped - 7 lines]
> Resistance tests appear normal. For those who know a ton more than me:
> What would be your next steps if you were in my shoes? Thanks

Like you said, since the code appears immediately, the SBEC has found
an electrical fault with the AIS circuit, vs a rationality based
failure.

I would suggest checking all four wires to each other with SBEC and AIS
connectors disconnected for possible shorting. Then check them all to
ground for a short.

What do you actually read on the Y/B wire? It's possible that your
original AIS had a shorted coil that destroyed the SBEC driver. My
instinct tells me you have a bad SBEC which is uncommon, but a shorted
AIS could cause it's failure if Chrysler didn't incorporate adequate
circuit protection into the computer.

Toyota MDT in MO

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