Slightly rough idle on '92 190e 2.6

[scotth_uk]

Hi All,

I've recently purchased a 1992 190e 2.6 with 140k miles on the clock. The car seems in reasonable condition and has been running very well. I've had it 'serviced' by my local garage, which was filters and fluids.

My concern is that every day the idle is becoming just a little less smooth. The idle speed on the car is roughly 600-650 by the tachometer, and the oil pressure shows between 1.8 and 2. Put your foot down and it's smooth, and there are no signs of misbehaviour at any speed other than idle.

I have read plenty about idle control bits and pieces, but keeping in mind that I am not particularly mechanical I'm not sure I fully grasped the concept. :-(

Would any of you care to offer suggestions, and perhaps assist with your experiences in similar scenarios? It would be much appreciated.

 

[jimmy]

Seeing as it is electronic fuel injection there is little you can do to adjust things like you could on carburrettor models, everything should look after itself and adjust accordingly unless there is a faulty component.

Check with the engine running to see if any of the ignition leads are arcing out out or breaking down. Might be worth changing the spark plugs and the ignition leads, if that does not cure it then probably something more complicated.

Spark plugs are the usual suspect when it comes to poor or rough running, manufacturers recommend longer service intervals but this can cause problems. I have seen many Mondeo Zetec engines where the plugs have been left for 50K miles and you cannot remove them, quite often results in broken plugs left in their threads, and the only way to remove them is by removing the head.

 

[UKEvo]

There are a few things that can influence idle quality. The idle regulator may need to be removed and cleaned out with either carb cleaner or brake cleaner.

The airflow meter may need to be cleaned along with the throttle body underneath as they always gunk up.

You can clean the AFM and throttle body by squirting some brake cleaner/carb cleaner around the air flow meter with the engine running, or you could use redex.

Good idea would be to get a brush and clean thoroughly with a toothbrush removing all the built up gunk. I gather the oil and air filter was changed recently if not replace them and the spark plugs. Make sure you have the plugs gapped correctly.

You can clean about 80% of the above with the exception of the idle regulator which you'll have to remove. Try the stuff below first.

The picture above is of my 2.5 16v 4cyl but most of the components are similar. In the centre of the image, resembling a tower with a bar crossing it, rubber stop in the middle - thats the air flow meter. The air filter sits on top of it. You'll need to remove the filter first to see the AFM. Inside the AFM venturi there is a plate, you can push that down and clean the air flow meter around where the plate normally rests. If you push down the plate as far as it goes, using a torch you will be able to see the throttle body and the closed throttle plate/butterfly. Pull the accelerator linkage and you'll see the plate open. See if you can get the toothbrush in there and clean it all up as much as possible where the plate seals to the wall of the throttle body. It's tricky but you can do it. Best practice of course it to take the AFM off, clean it, remove the throttle body and clean that but you might not want to go that far.

Of course it could also be a fuel problem. Have the injectors been replaced? Run a bottle of STP injector cleaner through it with a 1/4 tank of petrol - repeat. Normally you'd get about 100,000mls out of a set of injectors. I would change the spark plugs every 10,000mls for best performance.

It could also be a tuning issue, running too rich. How is your fuel consumption? Pull a spark plug, what colour is it? Black& sooty? 190's have CIS (continuous injection system) which is mechanical with basic electronic control via fuel pressure regulation it is not an "EFI" system with electronic injectors. Idle mixture is set mechanically, idle speed is electronically regulated by the ECU controlling the idle speed regulator largely from feedback from the engine coolant temperature sensor. BTW is the problem the same no matter the operating temp of the engine? ie Cold start, cold idle, hot idle?

Any questions about the above just ask.

HTH
Neil

 

[scotth_uk]

Thanks for the help guys. I will try a few of your tips this weekend and see how I go.

 

[stwat]