Drifter

Recap:

“Cruising my way cross-town today with my a/c running. Temperture was about 95 degrees. I came to a stop; the light had just turned red so I put the car in neutral to wait out the light. The cars temp gauge was reading normal. About a minute after I stopped the car stalled. I tried to restart it and it would die immediately. I turned off the A/C switch and it started & ran normal. After a minute or so I put the A/C back on with no further problems. This has happened several times only on hot day when the A/C is running.

On other occasion a similar stalling has occurs when I come to a fast stop, also with the A/C on.”

“When I rev my engine to about 3000 rpm’s with the a/c and headlights on, all my lights including dash and interior, dims down at about 1000 rpm’s when the revs are returning to idle. It sometimes stalls the vehicle. I also suspect it to be the cause of my vehicle sometimes stalling when coming to a fast stop.

It doesn’t appear to do it with the a/c off.

Note: I lubricated the ISV (Idle Stabilizer valve) and no change.”

“My idle decreases slightly when I turn on the a/c. Is this related to the auxiliary air valve for A/C?”

“My idle decreases slightly below my usual 600 rpm idle when I turn on the a/c. I was told today that the ecu controls the idle via Idle Stabilizer Valve (ISV). What do I need to check to isolate the source of the problem, before buying a new ISV?”

After a response from Rich9928p aka. www.electronikrepair.com.

“Dave,

If your idle speed is too low, you may need to check to see if your 928 has the correct LH fuel injection controller. The GT LH has a different ROM that provides a higher idle RPM and max engine RPM. If you don't have a GT specific LH it is possible that your GT engine can't support the extra power draw of the A/C compressor at too low of an RPM.

I've had several GT customers send their LH modules to me for rebuild that were not GT part numbers, probably because the GT LH purchased for replacement were not available. I reprogrammed their non-GT EPROMs with the proper GT ROM code all were happy!

FYI, for your 1989 GT, the correct module part numbers are:
LH p/n: 928.618.123.14
EZK p/n: 928.618.124.22”

I found that my 89 GT’s LH module 928.618.123.14 was at some point switched with a S4 LH module 928.618.123.13.

I got some second opinions and was told several times “I do not believe that your low idle problem and stalling are caused by the LH/EZK”.

However reading thru the “Service Information Tecknic” for the 89GT & S4, it supports that there can be a conflict.

Quote from the “Service Information Tecknic”;

“The part numbers of both engines control units have been changed due to
modifications in the software of the control units (idle speed, 6800 rpm
speed limit by interrupting the injection signal, different ignition curve
family, etc.).

S4 engine idle @ 675 rpm
GT engine idle @ 775 rpm

S4 max. Engine speed @ 6600 rpm
GT max. Engine speed @ 6800 rpm

S4 max. Engine power @ 6000 rpm
GT max. Engine power @ 6200 rpm

S4 max. Engine torque @ 3000 rpm
GT max. Engine torque @ 4100 rpm

M28/47 engines have modified camshaft.
~ 1mm higher cam
~ New cam shape

The timing is changed as compared with that of previous four-valve engines of the eight cylinder model series.”

I decided go with Rich @ www.electronikrepair.com. For $160.00 service & shipping, I could not pass up my Sharks brain transplant. I sent my LH module to reprogram the EPROM software on a Thursday and had it back on Tuesday!

My Shark feels much different now. More power, more rpm range, no stalling.. With or w/out a/c, idle does not decease below 800 rpm’s even on an abrupt stop, no more lights dimming, engine temp seems cooler!

My thanks to everyone’s input, special thanks to Rich for job well done.

Rich9928p

Dave,

Thanks for the kind words! Another 928 GT is running the way it should. It is amazing that just one digit in a part number can make such a difference.