Mk3 ls400 misfire when warm

[Mr Ponkerson]

Hi folks,

I've done a fair few searches on this and just after some confirmation that the fella working on my car is likely to be correct.  My car has developed a misfire once warm and the revs drop below 1k.  The idle is eratic/rough and it splutters on acceleration on part throttle and bogs down and splutters even more on full.  This first started after the car was serviced.

 I initially put this down to non OEM plugs so ordered denso ones and got new leads - this made no difference.  He's been looking more over this past week and had found and replaced a split hose (vacuum I think) which has improved things but it's still really not running right.

He's certain it's due to the blowing exhaust between the two O2 sensors causing ecu confusion, but reading everything on here I'm not sure a simple.blow in the exhaust (the usual flange deterioration) would be enough? Or is it more likely a duff sensor, edu capacitor leakage? I had also managed to get a couple of error codes for the air intake temp.sensor and air flow meter.  Not had time to check again since the hose has been replaced.

As an aside (in case it's relevant), the temp gauge has never really properly worked on the car (occasionally kicking in to the bottom of the gauge but nothing more), he replaced this at the same time as the second set of plugs but nothing has changed except that it seems a little more willing to get to this bottom of the gauge point.

 

Apologies for the long winded message 

[Bluesman]

It was the sensors you mention that was my misfiring and I had both replaced and problem solved. They were replaced with Lexus parts.

[Ben01]

Leak between the O2 probes could confuse ECU and makes nasty idle, but if it is realy bad, it should drops error on cat or probes (like P0420).

If there is no error on cat/probes, but a bunch of errors on inlet, stay focus on inlet. Air temp sensor and air flow meter HAVE TO be fixed (or any reason they throw errors has to be fixed, it could be sensor, electronic/electric, "pneumatics", etc), before any move (and cost) further, to O2 sensors, ECU etc.

If temp gauge is dead the coolant temp sensor could badly fool ECU too (I don't remember if this LS has two ECT sensors or common one for gauge and ECU).

In whole picture, it could be nasty and/or stupid electrical problem, like broken harness core or in-plug pin, or smth like this - it is not normal you lost a few sensors at once, they probably lost the common power supply or similar problem.

[Mr Ponkerson]

Thanks guys, I'll pass this on (and will recheck engine codes)