[allyv8]

Failed Oxygen sensors will not cause poor starting - the engine ecu will not run closed loop off the Oxy sensors for at least 10 - 15 secs.It fires up on info from the crank and cam sensors,coolant/air and fuel temp etc.When it gets to 500 rpm it will start to look for a Maf reading too.A session on testbook will show up most likely causes of the poor running.

 

[allyv8]

You dont need the Rovacom to check if the Oxy sensors can switch,a volt meter is good enough to see if they switch down to 0v - rich from 5v.Hook up to the black wire on the sensor and to earth.If the oxy sensors fail to switch at all it will run very rich.

 

[allyv8]

I didn't see the starting issue.

I still am going to disagree, while it is a closed loop at start up, if the air mixture is still not right, then it can cause abnormal start up.

But its not closed loop on starting,its a fixed map from mostly coolant temp.For the mixture to be too lean at cranking there would have to be low fuel pressure or similar - but nothing to do with closed loop control from Oxygen sensors.

 

[allyv8]

You need to forget anything to do with the Oxy sensors in terms of starting issues,they simply are not hot enough to switch with out at least 10 secs worth of heating - even after restarting immediately,and even if they did work the ecu would not be looking for their input till it decides to swop to closed loop.
Look elsewhere,fuel pressure,pump relay,crank sensor,fusebox etc,etc.

 

[allyv8]

Where did the Cats come from ? Since the fault has only been there after they were fitted I'd try taking out the upstream sensors,leave them plugged in and hanging down.Then see how well it starts,I'm thinking there could be too much back pressure - if it fires straight up you have your answer.
Here in the UK aftermarket Cats have been causing allsorts of problems.