MAF erratic readings

Tiny
GRAEME PARKER-WILLIAMS
  • MEMBER
  • 2011 VAUXHALL ASTRA
  • 1.7L
  • 4 CYL
  • TURBO
  • 2WD
  • MANUAL
  • 77,000 MILES
Mass air flow readings constantly fluctuate from 2g/s to 14 g/s at idle and fluctuate across all rpm ranges.
Friday, February 7th, 2020 AT 11:52 PM

21 Replies

Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Are you experiencing a fluctuating idle also? If it is hunting at idle, ie the engine revs are fluctuating i would advise first checking for intake leaks.

Here is a guide in the link below that will run you through the process:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I would also advise cleaning your MAF sensor, here is another guide for this process:

https://www.2carpros.com/articles/mass-air-flow-service

Let us know is you have any further questions and what you find after either of these processes.

Regards, Joe
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Saturday, February 8th, 2020 AT 7:41 AM
Tiny
GRAEME PARKER-WILLIAMS
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The car idles fine at 850 revs and does not fluctuate. There is a slight loss of power at revs under 2,000 but okay afterwards. I have cleaned MAF but still get the same fluctuations. I have replaced the MAF with a new one, but I still get the same fluctuations in MAF readings. I could not find any leaks but only had a quick visual.
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Saturday, February 8th, 2020 AT 1:57 PM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

What scan tool are you using to check the MAF reading?

Just to rule out an issue with the live data you are getting with the scan tool I would say try and borrow another scan tool to check against to verify.

With the readings you are getting you should be experiencing an unstable idle.

If it checks out then the next step would be to check for air leaks as in the guide in my previous message.

Regards, Joe
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Sunday, February 9th, 2020 AT 4:25 AM
Tiny
GRAEME PARKER-WILLIAMS
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Thanks. I am using an obd2 and the torque app. Would an air leak cause these readings and no other symptoms apart from a slight lag below 2,000 rpm's? I have checked for air leaks using carburetor cleaner but found nothing. What else could be causing it? I will try a different scan tool.
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Sunday, February 9th, 2020 AT 6:28 AM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Please do try a different scan tool and let us know.

If you can access a vacuum gauge I would advise checking what readings you get. Does the needle on the vacuum gauge fluctuate?

Also what are you getting from the MAP sensor live date, does this also fluctuate?

Regards, Joe
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Sunday, February 9th, 2020 AT 9:53 PM
Tiny
GRAEME PARKER-WILLIAMS
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I don't have a vacuum gauge so unable to check that at the moment. I have used two different obd2 readers and two different apps the MAP does not fluctuate have attached a screenshot of about one minute on idle.
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Monday, February 10th, 2020 AT 12:05 AM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Just to rule is out have you checked you intake for obvious damage/restriction?

Follow all of the intake pipe work and check for anything loose or damaged.

Checked the engine air filter?

I would also check the entire air intake for signs of oil leaks. An oil leak around the air intake system can point to a boost leak.

Regards, Joe
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Monday, February 10th, 2020 AT 8:08 AM
Tiny
GRAEME PARKER-WILLIAMS
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I have inspected the air filter box and filter, checked for any loose pipes and cannot find any. I had a look in the throttle body and a little bit of oil was present. I also took the revs from idle to 2,000 then 3,000 revs and the MAP readings hardly changed. Is this a bad MAP sensor causing the issue? See attached graph.
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Monday, February 10th, 2020 AT 8:55 AM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Can you please remove and clean the MAP sensor?

I do not have the information for your specific vehicle but a quick search online should show you the position on the intake.

It is likely that oil residue has clogged the transducer on the MAP and is causing it to not respond to the changes in pressure.

Let us know what you find.

Regards, Joe
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Monday, February 10th, 2020 AT 9:24 PM
Tiny
GRAEME PARKER-WILLIAMS
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Hi,

I have cleaned the MAP sensor and I am now getting readings up to 250kpa. The MAF readings still fluctuate. The strange thing is that during a regen today the MAF readings were stable. Regen happened after 10 minutes of driving. Regen is happening after every 50 or so miles bit it's mainly short journeys.
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Tuesday, February 11th, 2020 AT 8:04 AM
Tiny
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Hey GRAEME PARKER-WILLIAMS,

This points to a potential blockage in the DPF. It could also be an issue with EGR valve sticking.

Can you please unplug the EGR valve and see if the MAF readings even out?

Regards, Joe
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Tuesday, February 11th, 2020 AT 8:58 AM
Tiny
GRAEME PARKER-WILLIAMS
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Unplugged EGR, still the same MAF readings. Unplugged MAF engine ran the same. On the emissions test on the app it says EGR failed not sure what that means.
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Tuesday, February 11th, 2020 AT 9:54 AM
Tiny
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Hey GRAEME PARKER-WILLIAMS,

I would advise removal and cleaning of the EGR valve.

The EGR being stuck open slightly could be causing the fluctuations in the intake that you are seeing.

Let us know what you find.

Regards, Joe
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Tuesday, February 11th, 2020 AT 1:20 PM
Tiny
GRAEME PARKER-WILLIAMS
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Going to remove and clean EGR this weekend. Do I need to reset ECU after new MAF.
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Thursday, February 20th, 2020 AT 7:25 AM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Perfect, let us know what you find there.

If you could send us a picture of the condition of your EGR valve that would be great.

You do not need to do a reset after replacing the MAF.

Resetting the long term fuel trim will make it quicker for the relearn to happen but it is not necessary.

Deleting the fault codes is a good idea so you can retest to ensure the fault is clear.

Regards, Joe
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Thursday, February 20th, 2020 AT 12:35 PM
Tiny
GRAEME PARKER-WILLIAMS
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Cleaned EGR it had a covering of carbon but not excessive. Car runs better but still erratic MAF readings not much else for me to check.
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Sunday, February 23rd, 2020 AT 10:33 AM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

If you clear down the fault codes and drive it do you now have any codes present?

Can you get any data for the soot loading of the DPF on your scanner?

How does the vehicle drive now? Are you still experiencing a lack of power?

What is the general use of this vehicle ie. Is it mainly used for short journeys?
Shorter journeys will increase the speed at which the DPF fills with soot.
If it is trying to regenerate it may be pointing to the DPF being loaded.
You may be able to force a regeneration if your scanner has the function or driving the vehicle on longer highway journeys may give it enough time to regenerate.

Regards, Joe
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Sunday, February 23rd, 2020 AT 3:43 PM
Tiny
GRAEME PARKER-WILLIAMS
  • MEMBER
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Hi, no fault codes stored, car is running better now slight lag before turbo. DPF is showing 72% after 58 miles. The car is mainly used for short journeys with one long trip a month. The car will regen when the load gets above 90% I then take it for a run to complete. It regens to 32% but according to the workshop manual this is what Asta 1.7 Cdti's regen too. I am going to try a completely different scan tool as the MAF readings are still all over the shop without any cause. I am getting an EGR error as per image not sure if this is okay.
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Sunday, February 23rd, 2020 AT 10:54 PM
Tiny
JOETECHPRO
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Hey GRAEME PARKER-WILLIAMS,

Please do keep us updated with the information from a different scan tool.

If you have a lack of power and the DPF is attempting to regenerate that often it sounds like the DPF being clogged due to the short drive cycles may be the problem.

Ash accumulates in the DPF if driven on short journeys too often and it can decrease the life of the DPF. Really a diesel vehicle with a DPF should only be used if it will do regular long trips. That or more regular DPF regeneration will be necessary.

Can you force a regeneration using you scan tool?

How dirty was the MAP sensor when you removed it?

Another problem with modern vehicles with DPF's running a lot of EGR to reduce emissions can be coking up of the intake. Especially on vehicles driving shorter journeys.
You generally would see alot of build up when you removed the EGR valve in these cases.

Your vehicle also may have a variable intake or fitted with swirl flaps.
It is not uncommon for the actuators on these to fail on if they are vacuum actuated vacuum pipes leaking. Excessive carbon build up can also cause the flaps to stick.

Again sorry I do not have the specifics for your vehicle but I would advise ensuring the actuator for the swirl flaps/intake works correctly if fitted.

Regards, Joe
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Monday, February 24th, 2020 AT 2:50 PM
Tiny
DRXANDER
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Hi, I have the same problem with fluctuating MAF sensor values. Did you solve the problem?
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Sunday, August 20th, 2023 AT 9:26 AM

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