I'd be very grateful for a bit of help with an erratic idle, which I haven't been able to pin down. My car is a lovely 2.0 ts 156 which used to occasionally stall at junctions or in traffic, but now merely idles erratically between 250-1500 revs. Any ideas or help much appreciated... Runs beautifully otherwise.
You need specialist equipment to test these sensors properly. Does the problem happen from cold ? For about the first 30 seconds after startup the lambda sensor is not up to temperature so its signal is ignored. If the problem happens within this window then its probably the air mass sensor.
Do you have a "fly-by-wire" throttle on your model ? Sometimes you have to do a reset if the EMU looses track of where the throttle plate is and this can cause a hunting idle too.
James, before replacing the MAF, check the throttle body if it's full of grimes or deposits. If it's dirty, clean it with carb cleaner and see if that helps. Also check the MAF for dust build-ups, it may cause the sensor to malfunction.
I don't reckon it would be the AFM, but to rule it out you can disconnect it. The injector light will show, and it may feel a bit rough at low idle revs, but drive around with it disconnected for a day and see if it still erratic.
If it turns out to be the AFM and its the same as fitted to the 145/146/155 2ltr 16vs, I have a spare second hand one which could be purchased for a very reasonable sum
James, before replacing the MAF, check the throttle body if it's full of grimes or deposits.
Exactly right. For the price of can of carb cleaner try cleaning the throttle body first. Its a really easy job and should be the first step before trying anything else. Just disconnect the large rubber pipe from the main throttle body and spray all over the exposed butterfly valve. Carfully open the valve with your finger (don`t force it - do it slowly) to get the spray inside. Wear a glove BTW or you will give your hand some horrible cancer or something.
Unless you have the proper tool for re-fitting you will need a 70-90mm or 80-100mm jubilee clip to replace the snap-fit metal clip you have at the moment. Any engineering merchant will have one, but car shops usually don't.