ECM fault?

[Programmer]

If the O2 sensor is contaminated, it's usually coated with a white powdery
coating, and will result in a high but false O2 reading. This'll command
"lean" from the PCM and fuel will be reduced.

A sticking TPS (over 1.25V) will disable idle control from the ECM

If the IAT sensor differs from ECT by more than 5 degrees, check for high
resistance in the ECT circuit or the sensor itself. Cleaning the IAT probe
can help, too.

If your brother has a scanner--what's the long term fuel correction doing at
idle ? Has anyone confirmed mechanical condition of the engine ? Sure you
may have 20" vacuum--but is it rock solid steady ? Does it fluctuate with
the change in engine "idle" speed ?

Is charging voltage consistent ? If the voltage varies at idle, the IAC can
actually change position, which results in poor idle quality.

Make sure A/C refrigerant pressure isn't too high if "idling" in defrost or
A/C on. A defective pressure switch can cause an unstable idle.

IS the scan tool receiving an A/C "on" request, though the A/C is off ?

IS the P/N switch showing correct position via scan tool ??

Here's some more to chew on...

Lyndon

-----Original Message-----
From: Akselrud, Boris <AkselruB at moodys.com>
To: 'gmecm at efi332.eng.ohio-state.edu' <gmecm at efi332.eng.ohio-state.edu>
Date: November 8, 1999 3:15 PM
Subject: RE: ECM fault?


>1. My brother owns an auto repair shop with all the tools including
>scanners. No trouble codes has ever come up, unless you disconnect
something
>on purporse.
>
>2. I don't know if such thing as fuel conditioner would make any
difference.
>Basically whatever my brother did in his shop with the engine did not have
>any slightest effect on idle behaviour. I could feel more power after new
>spark plugs, wires, distributor, timing set, fuel injector cleaner etc.
>However Idle behaviour remains the same: 2 sec or smooth running followed
by
>2 seconds of rough idle.
>
>3. I even was to a dealership with the intention to fix this problem. They
>responded that this is normal for that engine and even newer cars exibit
>stronger rougness (as well as charged me for the job they done and wich had
>no effect what so ever). However this is not the first V8 engine I drive
and
>I believe that this idle behaviour is certanly not normal.
>
>4. O2 sensor is new.
>
>5. Car has 110,000 miles.
>
>6. Could you explain what do you mean by was it "exposed to any silicone" ?
>
>Do these 5.7 TBI engines run rough at idle?
>
>Thank you for the responce.
>
>-----Original Message-----
>From: nacelp at jvlnet.com [mailto:nacelp at jvlnet.com]
>Sent: Monday, November 08, 1999 3:30 PM
>To: gmecm at efi332.eng.ohio-state.edu; gmecm at efi332.eng.ohio-state.edu
>Subject: Re: ECM fault?
>
>
>Try some good fuel system conditioner (ie Quaker State/Slick 50, only stuff
>that comes inna metal can).
>Has a complete tuneup been done?. All the electrical/wearable parts, at
>once?.
>Has it been on a scope, do you own a scan tool?.
>Personally I can't diagnose your car over the net,
>These are just a cople thing to look at.
>What shape is the O2 in, miles, was it exposed to any silicone?.
>Grumpy
>
>
>>Unfortunately no one answered my first post regarding what I think is ECM
>>related problem in 5.7 TBI in my 1993 Cadillac Fleetwood.
>>The problem is erratic or I would say unstable idle. Looks like ECM is
>>leaning the mixture (don't know for sure) causing idle to go below
>>comfortable level for 2..3 seconds followed by 2..3 seconds of smooth
>>operation
>>
>