Lq9 MAF sensor help needed!
Thread Starter
Teching In
Joined: Feb 2023
Posts: 48
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Lq9 MAF sensor help needed! Hey all. Ive been having an idling/maf sensor issue for the past week on my sled puller. It started out throwing a couple different maf sensor codes, so i purchased a (cheap) new maf sensor on amazon as i needed it for this weekend. Had the ecu out and my tuner went over it aswell found no issues. Im gonna try a data log at tonights fair, but the truck still throws a p101 maf sensor performance code. I can clear it and itll idle back down to 850 without issue, but after 30 seconds the truck will shoot back up to idling at 1200 rpm and stay there. Any ideas?
Note: up to 2 months prior to this, it NEVER had an issue idling.
Note: up to 2 months prior to this, it NEVER had an issue idling.
Good rule of thumb, at idle the maf should read about 1 gram per litre of engine size. So if you're a 6L should see about 6grams of air if I recall. You may be more if your idle higher than stock. Someone correct me if I'm remembering that wrong.
I "think" the pcm is comparing your MAF with an expected measurement based off of your MAP and throttle and RPM...? Make sure your MAP and TPS look right too, MAP should be around 100kpa key on engine off depending on your altitude.
I "think" the pcm is comparing your MAF with an expected measurement based off of your MAP and throttle and RPM...? Make sure your MAP and TPS look right too, MAP should be around 100kpa key on engine off depending on your altitude.
Thread Starter
Teching In
Joined: Feb 2023
Posts: 48
Likes: 1
Good rule of thumb, at idle the maf should read about 1 gram per litre of engine size. So if you're a 6L should see about 6grams of air if I recall. You may be more if your idle higher than stock. Someone correct me if I'm remembering that wrong.
I "think" the pcm is comparing your MAF with an expected measurement based off of your MAP and throttle and RPM...? Make sure your MAP and TPS look right too, MAP should be around 100kpa key on engine off depending on your altitude.
I "think" the pcm is comparing your MAF with an expected measurement based off of your MAP and throttle and RPM...? Make sure your MAP and TPS look right too, MAP should be around 100kpa key on engine off depending on your altitude.
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Verdad Gallardo Yep vac leak certainly would make idle high, not sure I've seen it throw that MAF code though but makes sense it could if large enough. Just going by what Ive seen.
Fuel trims will show adding a lot of fuel. Also your MAF won't show that 1gram per litre flow. Scan it up! :-) If 1200 RPM is LESS than 1gram per litre then yea bad leak or bad MAF.
Check that MAP though because I can see a scenario where a bad MAP could make the PCM condemn the MAF, and I believe once the MAF gets a code the PCM goes back to Speed Density mode where a bad map again would cause havok because I think it then ignores MAF completely.
I'm probably focusing on the MAF code too much and overthinking this whole thing
Fuel trims will show adding a lot of fuel. Also your MAF won't show that 1gram per litre flow. Scan it up! :-) If 1200 RPM is LESS than 1gram per litre then yea bad leak or bad MAF.
Check that MAP though because I can see a scenario where a bad MAP could make the PCM condemn the MAF, and I believe once the MAF gets a code the PCM goes back to Speed Density mode where a bad map again would cause havok because I think it then ignores MAF completely.
I'm probably focusing on the MAF code too much and overthinking this whole thing
Last edited by mk3cn4; Sep 27, 2023 at 07:48 PM.