Hunting idle RPM

[classicswede]

Spray carb cleaner of Lynx will do around all joints. If the engine note changes when you spray a joint it is leaking air.

Have you ordered the plugs I recomend?

[PeteBDN]

I have ordered (and recieved) Denso K20PR-U for a 2004 S80 2.4 normally aspirated. I intend to fit them early next week.

I will get some spray carb cleaner or Lynx.

Thanks classicsweede.

[PeteBDN]

I have changed the spark plugs, but the hunting at idle is still there. It is more stable when the engine is at normal operating temperature. When cold it is all over the place as it was before.

Haven't seen any hunting on petrol since the change, just on LPG. I have probably jinxed it now and it will hunt later on my way home!

I am going to look for air leaks next, gotta go get some spray first.


MOT next week, does anyone know if the hunting idle rpm is a fail?

[Joe Harding]

Might seem silly, but as the thread shows, you have done most of the obvious things. Have you checked the brake vacuum servo. If that has leaks, it will dilute the vapour, and this will show up most at idle. Try pushing the brake at idle and see if the engine stutters.

[PeteBDN]

Originally Posted by Joe Harding

Might seem silly, but as the thread shows, you have done most of the obvious things. Have you checked the brake vacuum servo. If that has leaks, it will dilute the vapour, and this will show up most at idle. Try pushing the brake at idle and see if the engine stutters.

Not silly at all, I will try it and see what happens, I have noticed the idle respond when the brake pedal has been depressed before, normally when the car is still moving but slowly, say 10 mph. Again it is intermittent so until your post I have never equated the two events as related.

Thank you

By the way, the car passed the MOT fine, adivisory for both front anti roll bar bushes.

[PeteBDN]

Originally Posted by Joe Harding

Might seem silly, but as the thread shows, you have done most of the obvious things. Have you checked the brake vacuum servo. If that has leaks, it will dilute the vapour, and this will show up most at idle. Try pushing the brake at idle and see if the engine stutters.

Have tried this lots over the last few days, and pressing the brake pedal is not causing the engine to stutter. The car is behaving a little better now the weather is warmer. I doubt that will last though!

[DXMachina]

Bringing up an older topic as my query is highly relevant to the discussion above

I've been running my V40 for 8 months now and am nearly convinced its a good one and worth the spend on the conversion.

In preparation I'm planning to get the new plugs, coils and HT leads that are always suggested, as well as sorting out other minor niggles the vehicle already had.

Its generally suggested to get the 2-electrode Denso copper-core plugs as suggested for the model by their online catalogue. My problem is that for a B4204S2 engine, Denso suggest using K20TXR - which is a nickel plug

Are the Denso copper K20PR-U's mentioned here and in several other threads compatible with my car? IE, are the threads the same and will I be able to just screw them right in ?

Cheers
Chris

[classicswede]

I have a new set of genuine Volvo HT leads I no longer need if they are interest. I also keep NGKspark plugs of the correct type for LPG. I'm not sure what the Denso number is taht will be needed.

It would have better to start your own topic. Perhaps a mod can split this off.

[Paul Newell]

Hi,
I've got a 1996 850s Estate. I changed the battery for a spare the other day so as to charge the spare. And the engine started hunting.
I've put the first battery back in again but this did not sort the problem.
It settles down a bit once it has idled for a few seconds but this is a bit disconcerting when at junctions, at the lights or slow manoeuvres like parking.
The engine revs drop rapidly when changing gear too which make changing gears a real pain as the rev's drop below 450. Even the kids have noticed that it runs really roughly.
Some of the symptoms are listed in other posts so I've checked for split hoses, lose clips etc but have found nothing so far.
Having said that when I disconnect the mass airflow sensor wires the revs return to normal (I haven't been brave enough to drive it in this mode yet). The mass airflow did not seem to be very dirty when I took it off for inspection.
The engine had new spark plugs, oil change with filter and air filter 2500 miles ago and has just done a 1600 mile French tour (more like a French road race as the average speed was in the mid 70's with, at one point, 185 miles covered in 2 hours) without any problems.
Does anyone out there have any idea's? Is this going to cost a fortune or is it something simple?

[classicswede]

Is the running off on petrol?

If the running is off on both fuels then I suspect the ECU might just have lost its bearings and needs some time to reset. I would try and do a decent run on petrol. When you remove teh power the petrol ECU resets all faults and returns the fuel trims to zero.

If it runs perfectly on petrol but only a problem on LPG then the LPG ECU could have lost its programming and will need setting up again.

What ECU type is the LPG system?