Hunting idle RPM

[PeteBDN]

Originally Posted by ajpaynter

I have had this trouble for a long time. It has been partly cured by disconnecting the new Mass Air flow sensor which had been fitted by Volvo in Malton. The engine management light stays on all the time though. It doesn't cure it completely but it is more comfortable than the terrible hunting & hesitation I had before. I don't know where to start looking for leaks in the air flow system.
A clean out of the ETM helped a bit at first but not for long.

Seems like a perfect description of my problem, it is at its worst when the engine is off the choke but not fully warm, when warm it can go for a hundred miles and not have an issue, but when coldish it does it about a quarter of the time and it is steadily getting worse!

[C70T5Driver]

I've just started to have exactly the same problem on my C70 T5 2006, at first I thought it was an LPG issue because the idle hunting seemed to sort itself out on petrol, but today it was hunting like crazy, far worse than before, racing between 100-1100 rpm even after i switched back to petrol before eventually settling down at 900 rpm. It is quite intermittent but seem to be getting worse

The LPG installer suggested I had a MAF Sensor problem, the dealer says they need to first try replacing both the O2 Sensors, and today I've been reading a lot about ETS issues which can cause this type of problem.

Needless to say the dealer wants a ton of money for the O2 sensor replacement and now it seems any problem I have is LPG related!!!

Any checks I can do to determine the root cause of this before I part with money to a dealer I don't really trust.

Many Thanks in advance.

[classicswede]

I'm fairly sure that replacing O2 sensors is just going to be a wast of money. A o2 sensor is either working or not. The readings on the OBD reader will clearly show if there is a problem. Again the MAF can be checked with the OBD reader,if failed it will not read normaly. If the readings are just off then cleaning will cure this.

The most common cause is the ETM and in most cases a good clean out will solve the problem.

I'd start with ETM and then try MAF is working blind (no reader)

[C70T5Driver]

Thank you very much for your help Classicswede.

Are you able to give me any guidance in how I go about locating, dismantling and cleaning the ETC. I'm no mechanic but can follow instructions pretty well if its a job I have the tools to do.

Do you know if there is thread which explains more about the ETC for my car and year, I did look through the ETC thread here but it seems to be a discussion for older models ?

I need to invest in a ODBC Reader will order one from amazon right now, just came back from a spin to the shops running on petrol and the car almost stalled at the lights, so I need to get this looked at asap I think.

Many thanks again, Richard

[classicswede]

The ETM is the throttle unit mounted under the inlet manifold. You need to remove it from the manifold and clean it up. The throttle plate is the main part that needs doing. The cleaner the better.

[C70T5Driver]

Thanks Classicswede,

That's my boxing day sorted out then, thanks again I'll let you know how it all goes.

Merry Christmas everyone

[C70T5Driver]

I finally got the time to strip down the ETM on my T5 56. Everything went well, hose came away easily with 4 screws holding the ETM in place, with 1 in a slightly awkward position which was a bit fiddly. I was a bit surprised by the amount of oily gundge in the hose and the unit!

Added a few pics, I should have taken one before I started the cleaning job, I used halfords carb cleaner.

Clean ETM, new oil, filters & plugs and the car runs very smoothly indeed on petrol & LPG, but I still have slight signs of hunting on LPG at idle - very much less of a problem than previously reported but noticeable.

I also got myself a code reader and it still reports P0100 Mass Airflow Circuit, my dealer has now said that the O2 sensors have not failed, just as suggested by ClassicSwede and they now recommend a new MAF - incredibly the OEM replacement MAF is not available until APRIL!!!

I have read that these can be cleaned also but I have no idea where I would find it; also with just over 150K I'm thinking that its worth replacing the O2 sensors anyway, is that sensible?

Any advice, as always, is very much appreciated.

[classicswede]

The MAF is located normaly onto teh air filter housing. It is held on with two screw and has a multiplg with the wires connected to it.

Typical case of dealers with no Idea on what they are doing. The MAF can be checked for operation via the scan tool. I would still recomend a clean but doubt you need a new one. You should be able to find info in the genral forums with in depth detail on cleaning teh MAF.

If your lambdas are working OK then leave well alone. Replacment sensors tend not to be as good as the originals. If it aint broke dont fix.

You could quite well have an air leak. This could be anywhere from between teh MAF and Turbo or from the turbo to teh cylinder head. Check every single joint. If you have power loss then could quite well be one of the boost pipes. If you have 100% power and no boost loss then it can only be somewhere between teh MAF and Turbo.

[C70T5Driver]

Many Thanks Dai,

Will have a hunt around for the MAF and check for air leaks as you suggested.

Cheers, Richard

[PeteBDN]

My hunting has come back with a vengance with the cold weather, has started doing it on petrol and LPG, up until a week ago it was just on lpg.

I have cleaned up the ETM valve as posted earlier in the thread.

I will have a look for air leaks soon, any advice on the best method for spotting air leaks?

New spark plugs have been ordered too as they are pretty much due change anyway.