A big plus 1 to getting the codes read. Invaluable at trying to figure out what's going on with these cars. I have a basic Torque Pro always plugged into both the XK8 and XKR. As a fixture.

This might be a silly question but I'll ask. After you received the ECU back and reinstalled did you (or the ECU repair folks) do a hard reset on the ECU? In thinking about it, removing and replacing them capacitors must or may have "reset" things but you might try a WHOLE CAR reset (if you haven't already) to flatten all the cars capacitors and start "afresh"...

Over the course with both cars, I have done O2 sensors, changed spark plugs, swapped TCS and MAF sensors etc and without a reset and the car just hates it. I mean, hates it.

I always amazed at the number of held adjustments the systems in the car makes to accommodate for wearing parts and things being out of wack. When ya get thing back in WACK the car is working on all this accumulated old info...and struggles.

The way I do the reset is to clip the cables together and then leave the key, the longer the better, in the RUN position while I do other things. My "logic" is that with the key in the ii or iii position the circuit is complete for many of the major systems in the car. I then turn to key to off and reconnect the battery as usual. Just a suggestion

 

^^

What code(s) do you see?

 

We’ll I went to the parts store today and used their scanner I was surprised to find out that there were codes logged. I guess my scanner is not compatible with this car which is kinda weird because I’ve cleared and read codes before!! Innova 3100a.

Anyways the codes that were present are 171 system too lean bank 1, 174 system too lean bank 2 and PO 300 random misfire & lastly P1316 Misfire is causing excessive emissions.

im assuming that this may be caused by an air system leak? But my question to the forum is can this cause random misfire and rough running at idle

 

An air leak is entirely consistent with the motor smoothing out as the RPM rises. You may have more than one issue, but I'd look at the lean codes first. A smoke test might be your best move to start with since there's no specific cylinder reporting a misfire.