air flow on intake filer cause rough idle...? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mtdave2 · 01-03-2022, 12:02 PM

I noticed that when my cooling fans come on at idle, my motor would start running rough. i figured out that it was air from the fan blowing onto the intake filter that was the issue. why I don't understand.

i moved the intake tube out of the line of the fan blast and all is fine, but id like to understand what is going on. I know others have their filters in the fan blast and don't have this issue.

I found I did have some vacuum hoses run incorrectly at first but have them all sorted out now, and the issue is still there.

i made a video showing how a small fan on the intake causes a rough idle. perhaps that is normal?

https://youtu.be/9Ig1KhCTtLI

LS short box · 01-03-2022, 06:02 PM

The additional air from the fan can "fool" the mass air flow sensor giving the ECM a false reading.

87chevy.com · 01-03-2022, 09:30 PM

double post

87chevy.com · 01-03-2022, 09:38 PM

is the ECU tuned for the different mass air sensor if not stock? that tube size is probably definatly not stock diameter.

when I bought the airraid universal maf card adapter, it was a little larger than OE. it would make it run like crap till the tables were tuned. this is a L83 motor which may be different than LS tuning?

look at the scanner and see what its showing..

Clint

mtdave2 · 01-04-2022, 01:10 PM

Speartech did the harness, tuning, and it is their intake tube and sensor. I've spoken with them about it they are stumped as well. perhaps a faulty sensor? it will send a code for the sensor when I put a lot of air in with a bigger fan.

in its current position, everything runs fine.

87chevy.com · 01-05-2022, 10:42 PM

absolutely unrelated, but thought I would share, I watched a youtube video while back on customizing something... wound up on a hose clamp mod / trick / hack or something or another.... dang it was stupid awesome.

(on the intake tube coupler)

harbor freight roll of heat shrink tube over the hose clamp, then shrunk down with the heat gun...
clint

LS short box · 01-06-2022, 06:00 PM

Very cool on the hose clamp thing.

01-03-2022, 12:02 PM	#1
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	air flow on intake filer cause rough idle...? I noticed that when my cooling fans come on at idle, my motor would start running rough. i figured out that it was air from the fan blowing onto the intake filter that was the issue. why I don't understand. i moved the intake tube out of the line of the fan blast and all is fine, but id like to understand what is going on. I know others have their filters in the fan blast and don't have this issue. I found I did have some vacuum hoses run incorrectly at first but have them all sorted out now, and the issue is still there. i made a video showing how a small fan on the intake causes a rough idle. perhaps that is normal? https://youtu.be/9Ig1KhCTtLI Attached Images __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban Last edited by mtdave2; 01-03-2022 at 12:23 PM.

01-03-2022, 06:02 PM	#2
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 2,132	Re: air flow on intake filer cause rough idle...? The additional air from the fan can "fool" the mass air flow sensor giving the ECM a false reading.

01-03-2022, 09:30 PM	#3
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: air flow on intake filer cause rough idle...? double post __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress Last edited by 87chevy.com; 01-03-2022 at 09:39 PM. Reason: edit

01-03-2022, 09:38 PM	#4
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: air flow on intake filer cause rough idle...? is the ECU tuned for the different mass air sensor if not stock? that tube size is probably definatly not stock diameter. when I bought the airraid universal maf card adapter, it was a little larger than OE. it would make it run like crap till the tables were tuned. this is a L83 motor which may be different than LS tuning? look at the scanner and see what its showing.. Clint __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress

01-04-2022, 01:10 PM	#5
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: air flow on intake filer cause rough idle...? Speartech did the harness, tuning, and it is their intake tube and sensor. I've spoken with them about it they are stumped as well. perhaps a faulty sensor? it will send a code for the sensor when I put a lot of air in with a bigger fan. in its current position, everything runs fine. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

01-05-2022, 10:42 PM	#6
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: air flow on intake filer cause rough idle...? absolutely unrelated, but thought I would share, I watched a youtube video while back on customizing something... wound up on a hose clamp mod / trick / hack or something or another.... dang it was stupid awesome. (on the intake tube coupler) harbor freight roll of heat shrink tube over the hose clamp, then shrunk down with the heat gun... clint __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress

01-06-2022, 06:00 PM	#7
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 2,132	Re: air flow on intake filer cause rough idle...? Very cool on the hose clamp thing.

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