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My 2005 st220 3.0 V6 starts to shudder an lose power at 3 or 4000 rpm. It has done 120k miles, this problem all of a sudden happened a few weeks ago and hasn't stopped since. The RAC plugged it in and said something about the catalysts running to lean and that it would fail an MOT on emissions. Could this be the reason for the power loss and what can be done to rectify the problem? I have also been told it could be the airflow indicator or the temperature gauge. Any clues as to what it could be would be much appreciated.
Thanks.
 

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I have the exact same issue with a 2.5 v6...

This is what I've done so far and it hasn't resolved the problem:

Replaced MAF
Replaced Lambda Sensors
Replaced Fuel Pump
Serviced it inc Fuel Filter
Removed Cat (suspected a blocked cat but was fine)
Disconnected the ECT as it was reading 144c for some reason, by disconnecting it the ECU assumes a default value
Checked hoses, LIM, UIM, gaskets and IMRC.
Checked Idle Control Valve
Checked Fuel Pump loom

ECU reports bank 1 and bank 2 running lean.

So don't rush in to doing the above lol...

If anyone's got any ideas? I'm all out!
 

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I did wonder... One thing I noticed a couple of times is that if I reset the ECU the first couple of high rev attempts seem to go well then it falls back in to the issue at hand...
 

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Sounds like an ECU fault on me.

Do you know anybody with the same car, that you could borrow an ecu from to try ?

It would be they only way you can be completely sure.

Chris
 

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Yeah I have my own v6 but tbh I rather not mess with that! Is it possible it could be a blocked pre-cat? The 3rd Lambda sensor reads higher than the other two, and higher than my v6 which has a decat. Is ECU faults common on the v6, I know theres a few known issues with the 1.8 and 2.0s due to their failing coil packs but thought the v6s were pretty solid.
 

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I have not heard anything in the way of ECU faults for the 220 or the 200


I know 3-4K upwards on the 200's is a sticking secondarys fault, they need a take off and good clean. but do the 220s have secondarys?
 

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Nope not on the 3.0 lumps. It's not the secondaries as it happens while they're open and sometimes before they'll open.
 
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