Variable and lumpy idling.
 

After the annual service (which included removing and cleaning the PCV box, which was described as full, but not completely blocked) of the 940 2.3 LPT, the idling varies that sometimes it is about 500 rpm and usually it is about 750 rpm. It is also a bit lumpy, as in the engine occasionally has a big shiver and the car rocks slightly.

Before the service sometimes the car would just cut out when idling, but that was very rare. Since the service there has been no cutting out.

Any thoughts on what is going on and what I could do?

A "Annual Service" including what exactly?

It sounds like a fuel side issue - the usual culprits include the throttle body requiring cleaning, vacuum leaks at the various signal level and intake hoses, and leaks at the injector seals.

Does it run ok under load ie when you are driving normally, or accelerating?

Have you checked the idle control valve (under the intake maifold)? They get crud build up so can't operate properly - i usually clean mine with a good blast of carb cleaner at each service. It's where i'd start, plus no harm in removing and cleaning it even if it doesn't fix the issue (really easy job to which is a bonus)

Also, when was the fuel filter last changed? And i'd second checking for vacuum leaks/gasket leaks with easy start or wd40? Possible something was knocked or loosened during servicing.

One last one, when i got my new wagon (well as new as a '97 can be lol) the idle wasn't great but a simple swap to v power (other premium fuels are of course available if the lawers are reading) has helped no end. I've put 3 full tanks of it through now and you can tell the difference - v power especially has a lot of cleaning additives (swear i don't work for shell... :tounge_smile:)

Hope this is of some help - good luck.

PP

What those two ^^^^^ said! :thumbs_up:

Also check the convoluted hose between the air mass meter (AMM) and the throttle body - i'd hazard a wild guess this was removed for improved access to the oil separator and/or the flametrap. If this wasn't replaced properly (or the clips weren't tightened) this will also give similar symptoms.

A quick localised squirt of WD40 with the engine running will also help you track down where the leaks are, the engine note will change when you squirt round the leak area.

Also check the throttle position switch is operating when the throttle is released.

All of the above should keep you busy for an hour or two today while you escape from the xmas preparations! ;) :D

Basic service, oil, filter, plugs. It runs fine under normal driving.

I am on to tank two of a switch to premium unleaded and will have a look at the other suggestions. Thanks.

Just an idea - check all the plug leads are secure on the plugs. If one is loose then at idle it may cause a misfire but be perfectly fine at higher engine speed.


Also next time the fuel gets low (nearly running out) add a couple of litres of meths to the fuel tank before adding a maximum of 2 galls (9L) of petrol. It's possible you have condensation in the tank and this is causing poor running at idle, the meths forms an emulsion with the water and allows it to be burned off instead of sitting at the bottom of the tank.
At higher revs you're usually moving so the water sloshes about and you get a more pure amount of petrol going through.

I added Wynns Dry Fuel and since then, there have various times when the car loses power. If I am idling the car cuts out. If I am on the move the revs die away and then after a few seconds come back. Is that the point where the water mix is being burnt off?

The plug leads were all fine.

The drop in idle speed to 500 rpm has stopped.

The lumpy idle is still there.

Meths is probably a lot cheaper than the Wynns stuff and does the same job. Ideally with meths you need a 10% concentration so 2L for 4 gallons (18L) of fuel for it to work.

The symptoms you describe suggest water in the fuel so the meths is worth a try. ;) :D

I decided to use Wynns as I work opposite a Euro Carparts and that is what they had in stock. Plus 2l of meths from the local Toolstation is nearly £7, the Wynns was £10, so not much of a saving.

It is clearly doing its job as I put it into a full tank, I have done about 70 odd miles and there has been three power losses.