Hunting Idle - MAF Issue Maybe?

[Gregski]

so I've been driving myself crazy over the past few months trying to tune out a small Idle Issue I have, not sure it's quite a hunting idle, but here's what the problem is:

Either in park or in drive my RPMs go up 50 or down 50. So I should idle at 550 RPM in Park, well I can see it drop to like 490 or go up to like 590 I also see timing go from 19* where it should be down to 16* or as high as 25*

I understand that the PCM adjusts the timing via the Idle Adaptive Spark Control aka Overspeed and Underspeed to pull the RPMs back to the desired Idle RPM, but I don't know what is causing the RPMs to be off in the first place.

My MAF grams per second may very ever so slightly 5.1 to 5.2 (and the frequency goes from 2527 to 2510 for example) and timing goes 21* to 20* so is that it? is that enough of a change and what can be done to make the MAF less sporatic, is it time for a new MAF?

My MAF is attached to the OEM air intake so it is the stock distance from the throttle body. I am using a cone air filter though i tried the OEM air box and stock air filter as well. Also I tried cleaning my MAF, I also tried a second MAF (same part number) I happen to have a spare and of course I re calibrated it, as it was reading up to 12% lean.

[sprint_9]

Does it do it when it stays in either drive or park, or as you shift from one to the other?

What are you running for exhaust.

Have you tuned on it at all? Do you have a wideband o2 sensor hooked up?

A cone air filter cold be enough to mess it up slightly. How long did you leave the stock one on after you switched it back?

[Gregski]

Originally Posted by sprint_9

Does it do it when it stays in either drive or park, or as you shift from one to the other?

It does it in Drive (stopped at a red light) and it does it while in park (sitting there in the driveway).

Originally Posted by sprint_9

What are you running for exhaust.

Dual 2 1/2 exhaust into Magnaflow mufflers. Hooker cast iron exhaust manifolds.

Originally Posted by sprint_9

Have you tuned on it at all?

yes I have calibrated the MAF

Originally Posted by sprint_9

Do you have a wideband o2 sensor hooked up?

I own one but it is not hooked up at this time.

Originally Posted by sprint_9

A cone air filter cold be enough to mess it up slightly. How long did you leave the stock one on after you switched it back?

Had the stock box on there for a few hours drove around with it like that, had no change.

[prodjay10]

What is considered normal? I wouldn’t say my idle hunts, but it does go from 520 or so up to 575 or so. I would consider that to be normal, you probably won’t see it on the factory tach, but I’m not sure. You can’t tell the truck is on since it doesn’t shake at all.

[Wildkarde]

Is this a electronic throttle motor or cable. If its cable, dirty IAC motors are notorious for causing idle hunting issues.

[Gregski]

Originally Posted by Wildkarde

Is this a electronic throttle motor or cable. If its cable, dirty IAC motors are notorious for causing idle hunting issues.

hmmm, thank you it's drive by cable, suggestions on how to cleanatize it?

[sprint_9]

Just to confirm that when you calibrated your Maf you had all the appropriate settings off so it wouldnt go into closed loop, etc? You also used your Wide band to calibrate the Maf table?

Have you tried reverting to a stock Maf table to see if that fixes the problem?

[Gregski]

Originally Posted by sprint_9

Just to confirm that when you calibrated your Maf you had all the appropriate settings off so it wouldnt go into closed loop, etc? You also used your Wide band to calibrate the Maf table?

Have you tried reverting to a stock Maf table to see if that fixes the problem?

I calibrated using the Closed Loop method relying on the STFTs + LTFTs and the narrow band oxygen sensors. I had the MAP disabled in the Engine \ Airflow \ Dynamic disable at this RPM setting by lowering it to 100 RPM

my MAF was reading 12% lean so I bumped my entire MAF curve by 10% to enrichen it and keep the smooth slope, now I am in the -1% to -2% range at idle and cruise so it looks great and I am on the safer side ie richer

I will tune the WOT with a wideband AFR gauge later, at this point I just want to take care of the annoying idle RPM fluctuations

[sprint_9]

Thats great to get it close and get you out on the road, I used a similar method to get mine in the ballpark. I was like 80% percent off out of the gate though.

Have you done any logging to slowly make changes to the maf table in order eliminate the maf error and zero it in, or have you just flat out add 10%?

If you just added 10% its likely that the cells you idle in are off a little bit causing your idle issues.

[Wildkarde]

You can clean the IAC motor with some air intake system cleaner and a toothcrush through the throttle body or remove the motor. I use a plastic bristled brush that basically a industrial grade toothbrush. the motor will smoke like a deisel rolling coal when you first start it back up.

[Gregski]

Originally Posted by sprint_9

Thats great to get it close and get you out on the road, I used a similar method to get mine in the ballpark. I was like 80% percent off out of the gate though.

Have you done any logging to slowly make changes to the maf table in order eliminate the maf error and zero it in, or have you just flat out add 10%?

If you just added 10% its likely that the cells you idle in are off a little bit causing your idle issues.

Thank you for the ideas and suggestions. My idle problem existed before I even started tuning / messing with the MAF.

I did the immediate 10% bump cause I saw Goat Rope Garage guy do a 15% increase on his when he saw his error being 14%. Then I did more data logging and saw the numbers all between -1% to -2% after two test drives of about 20 minutes each, steady gradual throttle changes trying to stay out of DFCO and WOT. Pic attached.

Don't worry it's not the only video I watched I actually paid for some training and read a ton as well. Even some of the instructors were perplexed by this idle issue although I don't expect them to tune it over the phone, chat, or email, ha ha.

[Gregski]

Originally Posted by Wildkarde

You can clean the IAC motor with some air intake system cleaner and a toothcrush through the throttle body or remove the motor. I use a plastic bristled brush that basically a industrial grade toothbrush. the motor will smoke like a deisel rolling coal when you first start it back up.

Thank you very much, I appreciate that.

I also found this video, seems inline with what you said, I really like this guy and how he explains things, drama free, ha ha:

How to Clean a Throttle Body and Idle Air Control ( IAC ) Valve - Quick and Easy

[Gregski]

Originally Posted by prodjay10

What is considered normal?

sorry I missed your post the first time around

550 RPM in Park is the commanded Target Idle Speed by the PCM aka normal - see pic below green section once the engine is at operating temp

525 RPM in Gear is the commanded Target Idle Speed by the PCM aka normal - see pic below green section once the engine is at operating temp

this is for a 2001 4.8L with 4l60e trans 3rd Gen obviously

Originally Posted by prodjay10

I wouldn’t say my idle hunts, but it does go from 520 or so up to 575 or so. I would consider that to be normal, you probably won’t see it on the factory tach, but I’m not sure. You can’t tell the truck is on since it doesn’t shake at all.

see if yours is 575 in Park and then drops to 520 in gear, that would be normal, but if you are sitting at a red light and the needle bounces aka hunts from 520 to 575 then you have the same problem as I do, ha ha

I would keep an eye on your timing in real time as well, perhaps sitting in your driveway idling in Park instead of at a red light of course, I bet your timing is dancing as well

most folks don't care but I'm a perfectionist plus I don't want to build on a shaky foundation if you will

[Gregski]

just wanted to provide a quick update, so I cleaned the throttle body and no dice, thank you all for trying to help I appreciate that very much, I am going to replace the IAC valve/motor next just to see what transpires

[OutlawDrifter]

I'm not familiar with your setup...stock 5.3? GM ECU? Aftermarket?

Both of mine move a touch, the Z28 has a good sized cam, but even the stock LQ4 in my '49 doesn't just idle at a SET RPM. It's easier to see in digital format then on an "analog" gauge.

[Gregski]

just a quick update spoke to a few pro tuners / instructors, and this appears to be normal, here's a quote from Andre Simon of HP Academy

"Yes that's totally normal. The ignition timing is used to help control the idle speed and as such it will jump around significantly in order to control engine torque."