Help....Lumpy idle on a 2.5

[Maxus]

Please help me!! My car is suffering from a lumpy idle. Happens when hot and cold. No problems starting. Runs nicely on the move. More smelly smoke than usual on tick over (not bad though). Ticks over slightly too fast (900rpm ish).

Have taken off the ICV and looked at the piston which moves as it should. Runs at 2000 rpm with it disconnected.

AFM flap not sticking and looks like its doing its job with the cover off. Runs worse if you tinker with the potentiometer.

Runs well on the move so don't think its plugs, leads etc

Haven't got any other inspiration from the Bentley manual.

Someone put me out of my misery. Any ideas?

[chu346]

Please help me!!

Someone put me out of my misery.

Come round to mine, I'll shoot you

If things aren't that bad, first clean everything out with carb cleaner, such as the ICV and AFM.

I'll let someone else take over from here........

[GDBN]

I just changed the temp sensors on mine. Has worked a treat on the tickover. Still a bit high when cold but when warm the tickover is perfect at about 650 rpm. It used to vary between 800 and 1000 but would stick all the time at about 1000.
The fuel consumption has drastically improved too ... even though the old one seemed to have the correct values across the terminals.
Guess after 19 years service they needed replacing.
G

[Sooty]

Got to agree with GBDN.
Coolant temp sensors are a well known cause of idle problems.

Two sensors at the front, RH side of the head, brown one supplies info for the temp gauge on the dash & the blue one sends info to the ECU for fuelling.

Using a 19mm, offset ring spanner, remove the brown sensor for easier access then change the blue sensor. Refit the brown one.
DON'T do as I did earlier today, and drop the crush washer into the depths of the manifold.

You will lose some coolant so have a top-up ready. You may also want to bleed air from the system via the bleed screw on the t/stat hosing (might as well while your in there).

HTH

Iain S

[Taylor325i]

Another possible cause is the rubber bellow between the air flow meter and the throttle body could be split. Check it thoroughly as it could be split underneath where it's not easy to spot. If it's split the engine will be sucking in un-metered air which will defo cause idle problems.


Taylor.

[Maxus]

Thanks all for the tips. I have had a new temperature sensor fitted so can take that off the list. Will take off the big pipe from the AFM to the throttle body and have a look underneath.

The AFM has been played with in the past so next step may be to try a new one of those after a tinker with the CO mixture on the current one.

I am a total novice when it comes to engines but I can thoroughly recommend the Bentley manual. Even I can follow it, although the problem is not solved yet.

[fannyj]

Coolant Temp Sensor = Thermostat ?
Where do i find it ?

[GDBN]

Nope ... the temp sensors are screwed into the top of the thermostat housing. One blue one for the ecu and a brown one for the dashboard temp guage.
You will see them easliy enough.

G