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What can cause rich idling?

scam75

scam75

Well-known member
Afternoon chaps

I have also posted this on TIPEC, following on from my ICV and chipset adventures, this is where i am now.

My car used to idle about 13 on my AFR gauge. It has richened up a bit over the last year or so. It seems to idle around 12.5 not long after start up and then once out and about and engine fully heated up it is nearer 11.5. I had suspected ICV and have been doing some cleaning in situ but starting to think it has nothing to do with AFR's. The car idles smoothly enough and on throttle all seems to be as it should be. I have no reason to suspect my AFR gauge is faulty as it reads as expected on throttle. I also run a SciVision MAF so do not have an idle adjustment screw. I calibrated my ICV as per Clark's Garage procedure at the weekend and the ICV seems to be working fine. Also worth adding engine is quite fresh after a recent rebuild and all manifold gaskets are new. Don't seem to have a vac leak either and in all honesty if I didn't have an AFR gauge I wouldn't be looking for an issue although there was a slight hunt at idle a few weeks back when I noticed it was super rich, 10.8 or something but other than that blip it idles as described above. I have also cleaned the throttle body and as mentioned the ICV has had a bit of a clean up and seems to work normally, when it was bypassed the idle went up to 1,100 rpm. I adjusted this with the screw on the TB and reconnected the ICV. Have also checked vac pipe on FPR and seems normal, no fuel smell. So what should I do next? Full car set up is in sig.

Cheers in advance

Stuart

 
Yes FPR could cause rich idle as could one ore more drippy injectors. Failing this it may be an idea to pop down the MOT station and ask them to stick the probe up its Khyber to see what is going on with an independant machine. You can find CO to AFR conversion tables on line.
 

ORIGINAL: Lowtimer

Have you checked that the fuel pressure regulator is delivering the correct pressure?
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No I haven't. What is the procedure for doing this and what readings should I be looking for? I have a 3 bar FPR.

Cheers

Stuart
 

ORIGINAL: robwright

Yes FPR could cause rich idle as could one ore more drippy injectors. Failing this it may be an idea to pop down the MOT station and ask them to stick the probe up its Khyber to see what is going on with an independant machine. You can find CO to AFR conversion tables on line.
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Yup 2nd opinion be good but I think my AFR readings are true as it's all good on throttle.

Stuart
 
ORIGINAL: scam75
Can the MAF sensor be cleaned? Spray it with carb cleaner maybe?
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Not sure, but I heard Bosch had a lot of issues with these MAF sensors on Alfa Romeos and Audis.
If needed the sensor shouldn't be too difficult or expensive to source.

FWIW I have one of the first SciVision MAFs on my S2 and it is still working fine after 10 years, but I religiously keep using the standard paper filter on this car.
 

ORIGINAL: TTM

ORIGINAL: scam75
Can the MAF sensor be cleaned? Spray it with carb cleaner maybe?
Click to expand...

Not sure, but I heard Bosch had a lot of issues with these MAF sensors on Alfa Romeos and Audis.
If needed the sensor shouldn't be too difficult or expensive to source.

FWIW I have one of the first SciVision MAFs on my S2 and it is still working fine after 10 years, but I religiously keep using the standard paper filter on this car.
Click to expand...

I've had mine about 4 years with no issues. Promax said when they go tits up they go massively lean through the rev range. This has not happened although I'm sure they could go tits up any way really! Maybe worth flinging on another FPR and see if that changes anything before I go MAF fault finding.

Stuart
 
Temp sensor in the head for the ECU on it's way out telling porkies to ECU about true temp ?
 
You know James that's a good shout! That would explain why it idles about 12.5 when still heating up and then down to 11.5 when fully hot. ECU being told it's cold and pumping in more fuel? Could also explain poor fuel economy?

Does anyone know what it defaults to unplugged? Does that make car think it's hot or cold? Oh and where is it??

Cheers

Stuart
 
Cheers. Is it part number 944 606 125 00? There are 2 of these according to PET. Where exactly is the DME temp sensor? Is it a 2 pin plug, one of those rectangular jobs with the square retaining clip?

Edit to add that is part number and it seems to be on the block under the throttle body. Porsch-a-part seem to be wanting £60 [:(] Seems to be a Bosch one and a FAE one from international sellers. (US and AUS). About a tenner for the FAE one and £15 for the Bosch. About a tenner for delivery. Will phone OPC tomorrow, might get a nice surprise!!

Stuart
 
The DME temp sensor is the blue one at the upper front of the block, below the coolant tube exiting the head going to the radiator.
 
Cheers Thom. Got one from OPC. £34 Inc vat delivered. Fairly sure this will be the culprit. Can it be changed easily enough or is there anything needing removed to get to it?

Stuart
 
Obviously you will have to remove some of the coolant, and maybe the coolant tube which is in the way to give room to the spanner. Should be comfortably doable in a couple of hours, beer excluded.
 
I did it, it was pretty simple in situ with ratchet spanners and some u-js for the socket set. I lost a couple of tablespoons of coolant that was all.
 
Good stuff, can cope with a couple of teaspoons of coolant being lost! Then the joys of bleeding it, although my driveway is on a good old gradient so that always helps the bleeding process. I will do it from cold for obvious reasons!! [:D]

Stuart
 
I was going to reply and tell you not to buy a FAE item, i fitted one and it lasted 12 months maybe !
 

ORIGINAL: Frenchy

I was going to reply and tell you not to buy a FAE item, i fitted one and it lasted 12 months maybe !
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Glad to hear that after purchasing a Bosch one! [:D]

Stuart
 
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