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Discussion Starter #1 (Edited)
Hi my Corsa C 1.2SXi Z12XEP has recently started idling slightly high. I noticed it the other day having been out for a drive for an hour or so and when I pulled up at home it revved up at around 1200-1300rpm.

It mainly seems to do it when warm and so I’ve just done the pedal test and the following codes have shown in that o

I had new coil pack and spark plugs at the end of Feb and have probably only done at most 2,000 miles since so the garage may not have cleared the P0300 & P0303 codes.

I’m wondering if the P0170 may be the MAF sensor and causing the high revs. I would be grateful for any thoughts/ideas.

Cheers.
 

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Any trouble starting? Taking off the MAF and trying a spray with contact cleaner (not WD40) is certainly worth a go and it's a top suspect. O2 sensor(s) could be the cause or a leak in the fuel line. I think people who know about such things might say that live data would be useful (not to me; I make no sense of anything like that) if you have the capability.
 

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Discussion Starter #3
Any trouble starting? Taking off the MAF and trying a spray with contact cleaner (not WD40) is certainly worth a go and it's a top suspect. O2 sensor(s) could be the cause or a leak in the fuel line. I think people who know about such things might say that live data would be useful (not to me; I make no sense of anything like that) if you have the capability.
No issues starting or idling when cold I don’t think it seems to just be when warm. I wondered the same MAF or o2 sensor don’t think it’s a leak in the fuel line as it’s not been going down any quicker. Do I just need to take the MAF off and spray then leave to dry? Can you recommend a cleaner?
 

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Well, I don't guarantee it's a fix, but there may be some contaminants on the sensor that you'll see poking down in the middle of the MAF tube that could send the wrong info. This is why WD40 and those types of water-repellent sprays are the last thing to use. Electrical contact cleaner will displace gunk without leaving a residue. Halfords sell a 500ml can for £4 but CarPlan Bright Spark is nearer £2 for 400ml, which is very plenty. Make sure, after spraying (it'll dry off really quickly) that you put the MAF back in the same direction; there's an arrow on it that should point from air filter towards engine. Otherwise, your sensor will be pointing the wrong way.

If that briefly works and your next step is to replace the MAF, get a Bosch; more expensive but the £20 ebay types are not liked by the C.
 

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Discussion Starter #5
Well, I don't guarantee it's a fix, but there may be some contaminants on the sensor that you'll see poking down in the middle of the MAF tube that could send the wrong info. This is why WD40 and those types of water-repellent sprays are the last thing to use. Electrical contact cleaner will displace gunk without leaving a residue. Halfords sell a 500ml can for £4 but CarPlan Bright Spark is nearer £2 for 400ml, which is very plenty. Make sure, after spraying (it'll dry off really quickly) that you put the MAF back in the same direction; there's an arrow on it that should point from air filter towards engine. Otherwise, your sensor will be pointing the wrong way.

If that briefly works and your next step is to replace the MAF, get a Bosch; more expensive but the £20 ebay types are not liked by the C.
That’s great thanks I’ll try giving it a clean first although can get a new Bosch one from eurocarparts for about £60 at the moment. Would this cleaner be ok https://www.eurocarparts.com/p/wynns-air-intake-carb-cleaner-500-ml-555770650?type=shopping&gclid=EAIaIQobChMIzNiUoezS6wIVmK3tCh1frg0xEAQYBCABEgJ54_D_BwE
 

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Never used it but, reading the description, yes it should do the trick.

A Bosch MAF for £60 sounds ballpark but (a) be on the lookout for suspect box printing, badly embossed printing on the part etc. I don't know about the MAFs but I have read elsewhere and on this forum that cheaply made copies of sensors, coil packs, even clutch kits masquerading as Bosch and other top brands are around and places like ecp and carparts4less have had them in (legal note - this is what I have read, not what I have experienced - just saying to know what to look for).

Secondly, a MAF clean resulting in problem solved indicates the grot was a likely cause and you might think a replacement soon or for JIC is prudent but... problem not solved doesn't necessarily = MAF is a total dud and must be replaced. There are other possibles and £60 is a lot for no difference to the result. I think (Marks152 will know for sure) that idling your engine (while warm, seeing as that's the issue) after disconnecting your MAF might be a free experiment worth doing. If your MAF is feeding false info, its absence could cause a default to "that'll do" calculations and the idle goes to normal. Then you'd have more of a pointer before spending. The can of cleaner, for a few quid, is something worth having in your kit anyway and, if I were to be taking it out for a look, might as well give it a spray too on the "might work and won't harm" basis.
 

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Discussion Starter #7
Never used it but, reading the description, yes it should do the trick.

A Bosch MAF for £60 sounds ballpark but (a) be on the lookout for suspect box printing, badly embossed printing on the part etc. I don't know about the MAFs but I have read elsewhere and on this forum that cheaply made copies of sensors, coil packs, even clutch kits masquerading as Bosch and other top brands are around and places like ecp and carparts4less have had them in (legal note - this is what I have read, not what I have experienced - just saying to know what to look for).

Secondly, a MAF clean resulting in problem solved indicates the grot was a likely cause and you might think a replacement soon or for JIC is prudent but... problem not solved doesn't necessarily = MAF is a total dud and must be replaced. There are other possibles and £60 is a lot for no difference to the result. I think (Marks152 will know for sure) that idling your engine (while warm, seeing as that's the issue) after disconnecting your MAF might be a free experiment worth doing. If your MAF is feeding false info, its absence could cause a default to "that'll do" calculations and the idle goes to normal. Then you'd have more of a pointer before spending. The can of cleaner, for a few quid, is something worth having in your kit anyway and, if I were to be taking it out for a look, might as well give it a spray too on the "might work and won't harm" basis.
Thanks again and that’s what I’m thinking for a few quid it’s got to be worth trying to clean it.

If it isn’t the MAF then I suspect the o2 sensor but these look to be around the same cost to replace. If it was this would that potentially cause issues not just when warm do you think?
 

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I don't know from exp, I'm sorry. I'm hoping Marks152 will chime in. He has this uncanny knack of reading a post and pinpointing the issue in one reply (he does fix a lot of cars so I guess he has a library in his head).

My line of thinking is that a MAF is easy to locate, undo, clean, run without so it's a good place to start whereas an O2 sensor isn't so much. One thing I have rolling around my head (and I may be wrong) is that a lambda sensor doesn't really get doing its job until it's warmed up. If so, and again my logic may be wrong, it's possible that the ECU supplies fuel on a "that'll do" basis because it's not hearing anything from the lambda, then your sensor gets up to temp and starts sending duff info so the ECU then dictates the wrong fuel level.
 

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Discussion Starter #9 (Edited)
I don't know from exp, I'm sorry. I'm hoping Marks152 will chime in. He has this uncanny knack of reading a post and pinpointing the issue in one reply (he does fix a lot of cars so I guess he has a library in his head).

My line of thinking is that a MAF is easy to locate, undo, clean, run without so it's a good place to start whereas an O2 sensor isn't so much. One thing I have rolling around my head (and I may be wrong) is that a lambda sensor doesn't really get doing its job until it's warmed up. If so, and again my logic may be wrong, it's possible that the ECU supplies fuel on a "that'll do" basis because it's not hearing anything from the lambda, then your sensor gets up to temp and starts sending duff info so the ECU then dictates the wrong fuel level.
I will definitely try cleaning the MAF first but I’m wondering if you’re right about the lambda sensor if it only starts sending info to the ECU when it’s warm then maybe it’s at fault.

I should have also said when the issue occurs if I press the accelerator and rev it very high it seems to then return to normal.
 

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I'm speculating on the lambda sensor, based on a bit of info rolling in my head. For instance, even if the theory's valid, if the Corsa has some pre-heater of some sort to get the sensor up to temp rapidly (I don't actually know - I would have to have an internet rummage) then that's my pencil-chewing thoughts down the pan.

Your other info puts thoughts like "throttle position sensor" and throttle body cleaning (I do remember a thread written on this by someone who does know what they're talking about - might have been Liviu2004 - as it does get manky) but I'm flailing around a bit without having dealt with or even handed over to my garage for a problem like yours (they're pretty tolerant of my dim questions and happy to lower my ignorance). There's this video, and your spray can is just the stuff:
 

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Discussion Starter #11
I'm speculating on the lambda sensor, based on a bit of info rolling in my head. For instance, even if the theory's valid, if the Corsa has some pre-heater of some sort to get the sensor up to temp rapidly (I don't actually know - I would have to have an internet rummage) then that's my pencil-chewing thoughts down the pan.

Your other info puts thoughts like "throttle position sensor" and throttle body cleaning (I do remember a thread written on this by someone who does know what they're talking about - might have been Liviu2004 - as it does get manky) but I'm flailing around a bit without having dealt with or even handed over to my garage for a problem like yours (they're pretty tolerant of my dim questions and happy to lower my ignorance). There's this video, and your spray can is just the stuff:
That’s great thanks again. Would the carplan bright spark cleaner you mentioned work for cleaning the throttle body as well as the MAF?
 

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Yes, it's volatile degreasing solvents (as is that Wynn's that you linked) that should make it a lot easier to shift off the grime and crud with a rag or, in the case of the sensor in the MAF, blast it off by pressure and dissolution, leaving nothing behind. The WD40 type of spray leaves a thin film of light lubricant which is not what you'd want on the MAF sensor. The other two sprays are good for all sorts of degunking and clean up unless it's important to have a lube film.
 

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Do you have any live data that we could see. Need to look at maf readings, o2's, fuel trims etc. If you could upload some data I'll take a look.
 

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Discussion Starter #14 (Edited)
Do you have any live data that we could see. Need to look at maf readings, o2's, fuel trims etc. If you could upload some data I'll take a look.
Hi thanks for reading my message and looking at this. I don’t have anything to get live data with what would be the best kit for me to get? In the meantime I’ve ordered some carplan bright spark as well.

I should say I know that the rear lambda sensor needs replacing as I also have the P0141 code showing but this has been on for a while and I’ve not had the spare funds to replace it and it doesn’t affect the running of the car as far as I’m aware.
 

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141 is a lambda sensor heater circuit, hence why the car still runs on it. Iirc code 141 is the second sensor(sits in the centre exhaust section).

Hope this helps.

You can disconnect the MAF sensor and the car should still run, maybe even improve...

Hope this helps

Cal
 

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Discussion Starter #16
My carplan bright sparks has arrived so I will have a look at cleaning the MAF this weekend.

I’m also tempted to get something to read the live data as suggested by marks152. What would you recommend to buy please?
 
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