just fixed the O2 sensor issue, see post "independent says bad ME1 module and though all was good (except for now knowing cats are gutted.)

Now have new problem(s) -

1. Hot start takes several tries and seems like engine is getting no fuel. Cold start is OK.

2. Warm idle is rough. Started out intermittent but is getting more and more constant. engine seems to miss up to 2000 rpm or so. Cold idle is OK.

3. Exhaust backfires slightly during freeway deceleration (foot off pedal, throttle fully closed) and can sometimes get it to do it at rest if I rev it and then take foot off pedal.

My question is this, could the lack of cats cause these symptoms? If the ECU is trying to lean out the mixture to compensate for the inefficiency (not there) of the cats, how lean will it make it? Will it go so far that driveability is compromised?

Also have a question about the cats. The code I get now is for main cats performance below specs, and the only way the computer knows cat performance is from the O2 sensors. It looks at the readings ahead of and behind the cat and evaluates the performance, I assume.

On many posts I have looked at, people refer to the cats near the exhaust manifold as "PRE-CATS". The ECU though is saying the MAIN cats are bad, not the pre cats. Based on where the O2 sensors are, the main cats are the ones closest to the engine, where the heat is, and where they can be the most efficient. The other ones farther back must be a "post" cat, maybe used to further clean up what the main cats may have missed.

Am I wrong in my thinking here? If the rears are the mains, how would the ECU know they were bad if there are no sensors behind them?

I searched for hours but there is little info on the newer cars (tons on the W124 though.)

Any help will be appreciated - Thanks in advance.