Over the weekend I was able to get a hold of an XJR ECU so I could diagnose my weird idle issue. (Idle's ok when IACV is unplugged, just no cold starts. Idle's at about 700rpm in drive/reverse and 800-900 in park/neutral)
My originall ECU part number is LNB 1410DD Date 11/11/02

The replacement ECU I got has a part number of LNB 1410DC/41R

I know there are a few different version of ECU's but I'm curious to know what the differences are...

After installing the replacement ECU, the car idle's fine but then occasionally (once every few minutes) it will start to misfire during idle and even while cruising on the freeway at about 70/75mph. Plugging the original ECU back in, no misfires but I get the high idle when the IACV is plugged back in

 

Here are the part numbers.

bob gauff

 

Each time you install a different ECM into the cars network you should perform an engine setup that includes throttle position and oxygen sensor orientation.

You can't just swap ECMs and get the same results from module-to-module.

You can use PDU, WDS, IDS etc to perform the setup.

Read the TSB about configuration.

bob gauff