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[Bourne]

Hi chaps,
            My 98 3.0 mv6 is running ridiculously rich ,so much so that it wont idle properly. Plugs are really sooty as is exhaust. I've tried another o2 sensor, first in one downpipe which made no difference so I replaced the second 02 sensor with the one I took out first assuming it must be ok.I've also cleaned the maf sensor and changed the the water temperature sensor just in case. None of these has helped.So unless I've got 2 dodgy o2 sensors (seems unlikely) I'm a bit puzzzled what to do next. Any ideas chaps? All suggestions welcomed. :-/

[hotel21]

Have you checked that the air filter is clean/new and the associated plumbing to ensure adequate air supply?

[TheBoy]

Is the EML on? If not, does the bulb work

If it is on, paperclip it.

[Bourne]

New air filter , pipes all clear, no eml. Have access to code reader ,no faults stored.Can't find any evidence of air leaks either.

[Kevin Wood]

It won't be in closed loop O2 control at idle so the O2 sensors don't come into the equation.

I wonder if the fuel pressure regulator is shot or the return line is clogged?

Are all the plugs sooty? If it's just a cylinder or two could be an injector problem.

Failing that MAF sensor? Would have thought it'd recognise the fault and go into limp home with sensible substitute values though.

Air or coolant temperature sensor? Again, would have expected it to substitute values and at least run but you never know.

Reading the fault codes would be a good move.

Kevin

[Kevin Wood]

Ahh, just noticed no faults stored  

Are you sure it's not an ignition related misfire giving a petrol smell and the appearance of richness?

Edited to say may be worth cleaning out the ICV in case it can't get enough air at idle.

Kevin

[hotel21]

choked/blocked fuel return causing over poressure of injectors?

[TheBoy]

Unplug the MAF, does it run better then (will bring on EML obviously)

[Bourne]

Every plug is sooty so not likely all injectors faulty. Have had icv off and cleaned thoroughly with carb cleaner.Don't think its a mis-fire as it revs perfectly as soon as you touch the accellerator. Will check fuel pressure as suggested.Have you seen a blocked fuel return line before ? seems unlikely somehow but worth a look as I'm starting to get desperate now.

[cem_devecioglu]

First bad idle problems can be caused by too many factors..And can be very complex..

The air fuel mixture problem (being very rich) also is another..As its the result decision made by ecu
from combination of responses from the censors..

As I have bad stories about working censors what behave different under bad wiring or different temperature ranges.

As a first step I would try connecting tech2 and watching the lambda sensor voltages and volumetric amount of air passing the inlet at idle..

And if these dont give any idea I would try to make the problem matrix  smaller checking crtical elements one by one..

Also MAF may be is worth checking twice..

PS:  Critical sensors is worth trying with a new one (without buying) but this can be done in a vx/opel dealer environment (once I did but they were not happy)

[JasonH]

What's the exhaust system like? They can suffer from blockages which means the engine still runs but at reduced power. I didn't even realise I had a problem until I changed the exhaust.