Poor idle on petrol

[GavinC]

'95 960 singlepoint Tartarini:

Increasingly, just now, on starting (on petrol) it idles fine till I press the accelerator to move off. At that point the smooth idle sometimes becomes a weak/powerless 'hunting' idle which will stall unless it then gets a sufficient bump on the accelerator to push the revs up to switch it to LPG before moving off.

Sometimes, too, it'll start with the 'hunting' idle. Other times it'll start perfectly. On a 'run' if I switch to petrol during a standing idle, at times it'll idle perfectly... at other times it'll idle with a 'hunt.' Whereas on LPG, it'll always idle perfectly.

Codes show 113 ("Late models injectors 1,2 & 4: wiring, fuse, injectors") and 511
("Long term fuel trim, idling: Intake/exhaust leak, fuel pressure, excessive fuel in engine oil, injector(s), EVAP canister purge valve, wiring, MAF sensor, ECT sensor, HO2S.")

Weirdly, merely clearing the codes appears to make it **temporarily** behave itself... for quite a few starts.

In every other respect the car runs normally on either fuel.

Could stale petrol be a factor?

Any ideas, please?

[MikeHill]

Hi, apart from the Wife's bifuel S80 I run a peugeot partner van with a tartarini conversion. an LPG service garage I have used talk about the petrol injectors becoming "glazed" when running on LPG, the van is a bit problematic on petrol when first started these days at Present I am trying injector cleaning additive in the petrol to see if that eases the situation.

I would recommend you take a look at http://www.volvoforums.org.uk/showth...hlight=jimthan
This could be the best way to improve the running - I'd suggest you contact him.

[classicswede]

I'm pretty sure you have basicaly answered your own gestion by stating the problem is resolved when you clear the ecu. I'm sure if you ran the car on petrol only the problem would not arrise.

It looks very much like your LPG mapping is out - not much of a suprise for a single point system on a 960. The qucik easy answer would to be to by and fit a ecu reset modul to clear teh ecu every time you switch off.

[Clifford Pope]

I've noticed this on my 240 with a single point system, and indeed there was a thread here about ways of automatically clearing the ECU codes.

Disconnecting the battery for a few seconds of course clears the codes, but is fiddly and loses other stored information like radio settings.
So I identified the feed wire to the management system under the bonnet (found by trial and error at the main black connector by the battery) and fitted a simple 2-pin plug with the pins bridged as an instant pull-and-replug way of resetting the codes.

I don't bother normally if I am going to be switching to gas very soon, but on longer trips on petrol (eg I've run out of gas with nowhere handy to fill up) it is worth resetting the codes before starting.

I have confirmed that the codes are indeed spurious ones arising from the rather primitive LPG system not communicating fully with the ECU, rather than real faults, because if I leave it on petrol, no codes ever appear.