Erratic data logging

[cortez2220]

When I try data logging or the dash, it gives many seemingly random numbers while occasionally showing values that make sense.
For example, the coolant temp (actually 203) will cycle through values like -40, 350, 120, etc.. and occasionally show the true value of 203. Its the same with all other data readouts as well.
I've played with the COM driver settings and found that setting the latency to higher values tends give a higher percentage of accurate readings but isn't much of a fix.
I'm using the Tunerpro RT V5 with a cable from aldlcable.com and the latest drivers for it. The car is a 1995 Olds 88 with the N/A 3800 S2. There don't appear to be any problems with the ecu as the car runs fine and local shop scan tools can read it fine. I'm also fairly sure I'm using the right definitions ($5B6).
Any help on this problem would be appreciated.

[Mangus]

Most likely another module in the ALDL line (digital dashboard, transmission control unit, etc) is also communicating on the line and needs to be silenced with a Mode 8 command. Make sure your definition includes this in the connection macro. This may be challenging if you don't have all the info you need, such as which module ID is causing the fuss.

Here's an example of a discussion about this.

http://www.gearhead-efi.com/Fuel-Inject ... t-607.html