Engine idle with CS 4” intake

[Speedie6]

My turner says the idling issues I’m having just the way it is with a 4” intake and aggressive cams. Sometimes it idles smooth as glass, particularly if the engine is fairly cool and it is moderately cool outside. But say I’m in stop ‘n go traffic on a hot day. The engine gets on the warm side. I’ll inch up to the next stop. The engine RPM will drop to near the expected idle speed, but, then jump back up to around 2500 RPM. Then it will bobble for about 15 seconds between 2200 and 2500 RPM. You hear the engine UUuuuUUUuuuUUuuuUU. Then drop back down to regular idle. Then repeat again at the next stop ‘n go. I asked my tuner who replied:

it’s when the vehicle is on the hotter side of things what you are experiencing is the Radiator Fans pushing air towards the intake. When this happens it’s adding air flow past the MAF sensor that is not a consistent air flow and only at certain times. This unfortunately cannot be tuned for and the issue is made more present with the larger diameter intake.

Do other people experience this? Is the tuner basically correct? I’m considering trying to stuff a honeycomb air straigtenerer into the MAF. It already has a basic standard style air straightener, so my guess is that it won’t help much, but I figured it wouldn’t hurt to try.

 

[L337TurboZ]

Try this. Take a piece of cardboard and block off the intake from the radiator fans. Make it so the fans push air away from it and see if the issue occurs again.

If that is the case maybe start making a cold air induction box kinda like how Volant makes one for the Silverado trucks.

This is just for reference
https://www.americantrucks.com/volant-pro5-closed-box-cold-airtake-0408-54l.html?utm_content=AT Intake - CAI|Volant&T5_Var4=T532541&utm_campaign=AT+Brands+Medium&dialogtech=ppc&utm_source=google-pla&utm_medium=shopping&T5_Var2=shopping&T5_Var3=red&gclid=CjwKCAjwyryUBhBSEiwAGN5OCNPgMm_hUo3jEA8ZP7HQE4f_5eoGgbAgkhx8ajZhbImAj11vo-rc4BoCtbMQAvD_BwE&gclsrc=aw.ds

If the filter box isn't an option due to space restrictions then hood vents and a deflector installed behind the fan could work. This is what the Corvette ZR1 has. It routes down and into the fan shroud.

https://i.ebayimg.com/images/g/AS4AAOSwBLlU5MEw/s-l400.jpg

 

[Cfoldone]

Only running a BNR S3, JBR 3.5" full path, Honey Comb air straightener. I use VersaTune and if you were able to get air flow / maf voltage your idle flows are almost flat line until about? 5% total air flow. So short answer yes, you will have low idle flow to partial throttle plate openings for maf to measure actual good flows. Flow speeds are a big change at low flow side of a stock 2.67" ? To 4" Intake pipe size. MAF just can't measure at very air flows.

 

[Enki]

Raising the idle to 1k will help a bit too. What brand and size filter are you running? I'd think this would be more of an issue with, say a K&N vs AEM Dryflow due to filter media density.

 

[Easter Bunny]

How is the battery. I had weird idle issues when my battery was dying

 

[L337TurboZ]

How is the battery. I had weird idle issues when my battery was dying

^
This is definitely something to check. If a battery has a bad cell or is faulty the ECU can lose it's stored memory causing weird issues. I've seen cars lose their theft deterrent settings for keys, throttle bodies becoming uncalibrated, and other wonky things.

 

[Speedie6]

Raising the idle to 1k will help a bit too. What brand and size filter are you running? I'd think this would be more of an issue with, say a K&N vs AEM Dryflow due to filter media density.

I don’t recall what the stock idle was, but it is already around 1300 or 1400. I’m using the filter which came with my CS, and they use AFE Pro Dry S filters.

How is the battery. I had weird idle issues when my battery was dying

Battery is good.

Try this. Take a piece of cardboard and block off the intake from the radiator fans. Make it so the fans push air away from it and see if the issue occurs again.

If that is the case maybe start making a cold air induction box kinda like how Volant makes one for the Silverado trucks.

I’ve often wondered why nobody, as far as I know, tried making something that looks similar to the stock air filter box, but for bigger intakes. But the hole that heads down to the wheel-well isn’t big enough to supply a 4” intake, I don’t think. But its an idea that I’ve mulled. If it could work, it would be a CAI. I guess I could look again, measure the hole and see how much area it really is. And just as an experiment, I could try the cardboard idea.

If the filter box isn't an option due to space restrictions then hood vents and a deflector installed behind the fan could work. This is what the Corvette ZR1 has. It routes down and into the fan shroud.

https://i.ebayimg.com/images/g/AS4AAOSwBLlU5MEw/s-l400.jpg

I’m not quite understanding how this routes, but, looks like it could be complicated. Of course we have the scoops for the stock TMIC and I’ve wondered if that could somehow be repurposed for an air intake. In fact, not sure if anybody recalls, but CS, in the early days, made an FMIC where they put a gigantic air filter where the TIMC is and used that for the air intake! My guess is, it didn’t actually work that well as they discontinued that design years and years ago. But it was still an inventive idea.

I guess just for a first try, I will get the honeycomb straightener. I don’t have much hope but it is pretty cheap and I guess worth a try. After that, I guess I will either just live with it, or look at something more exotic. And try the cardboard test.

 

[Enki]

Stock idle is 750...If you're idling at 1300 there's something wrong here.

 

[Easter Bunny]

The csgiant filter was found to flow worse than stock because of the convoluted piping

 

[Speedie6]

By the way, I'm also running a Cobb throttle body. And one reviewer on Cobb's site said that he found that it caused some idle fluctuations. So, with the huge intake and large throttle body and performance cams and large intake manifold, I might be forced to just live with some idle issues. Still, I hope to find some improvement.

As far as adding a honeycomb air straightener, first, I don't know if it will help any or not. Secondly, it wouldn't be easy to add. The included straightener is right at the end of the pipe just where the filter goes. See photo:

https://d1th1shy3lujuj.cloudfront.n...speed-6-4-inch-intake-system.jpg?t=1636590671

Well, I could remove the included air straightener but I don't think I want to do that. Or I could tack weld it to the included air straightener and have it sit inside the air filter. Will it help? I doubt much actually.

But, I've looked at the hole to the wheel well and after further consideration, I think it will supply sufficient air for a 4" intake. So building an airbox might help. I have some crap of my own located in that area that I can relocate. After that, there are various harnesses, gizmos and doo-dads that I don't even know what all they are in that corner. So I probably couldn't easily get an air-tight seal, but, that shouldn't be necessary. As long as it is generally sucking most of the air from the wheel well it should work. But it will be some work to make it. I can build some mock-ups first cardboard, then wood. Then the final probably out of composite sheets or something like that. I don't know how long it will take me to do that, probably a while. I'm surprised that nobody as far as I know had made such an airbox.

The csgiant filter was found to flow worse than stock because of the convoluted piping

Csgiant filter? I have no idea what you are talking about here. I have an AFE Pro Dry S filter which came with the intake.

 

[SyntheticAtmosphere]

Maybe not as air tight as you are lookin for, but I built one that pulls from the left front fender. here

 

[Speedie6]

Maybe not as air tight as you are lookin for, but I built one that pulls from the left front fender. here

Pretty cool! I guess you have the tools to do metal fabrication. I don't. But you did good work, thanks for the link. I'm sure that whatever I come up with will be much crappier, LOL.

 

[Speedie6]

Well, I made some progress. I looked at the idea of building an airbox. And it could possibly help lower BATs a bit. But I am now doubtful it would help much with my idle issues. The reason being that I think the air in the wheel-well is probably turbulent on par with the current location of the air filter. One reason, my fog light fake air vent is an actual air vent on my car as I made it vented because I have Damond's power steering cooler. And I've also had thoughts of maybe someday putting in an oil cooler. So I think the air in the wheel-well is pretty turbulent.

The issue that I was having, I can describe more accurately after further observation. When coasting, like when in stop and go traffic and the traffic is slowing down again, the engine would tend to fluctuate between 2100 RPM and 2300 RPM. This fluctuation was particularly annoying as you hear the engine UUUHHHHuuuuuhhhhUUUUUUHHHHuuuuuhhhh... Once coming to a stop, after a few seconds, it would settle down to its "normal" idle of about 1300 RPM. I know the idle is a lot lower on stock and near stock cars. But I don't recall, would I normally expect the engine RPMs to be a little high when coasting and then go back down to idle when fully stopped?

I really wasn't sure if a honeycomb air straightener would help or not, but I decided to give it a try. Leaving the Cobb air straightener in the MAF, I could stuff the honeycomb about 1/8" into the MAF. I used RTV silicone to hold it in place. See pictures below. The results were better than I expected actually. When coasting, the RPMs are still around 2100 RPM. But pretty steady. The engine UUUHHHHuuuuuhhhhUUUUUUHHHHuuuuuhhhh is mostly gone. And when I come to a full stop, I think it settles to the "normal" idle of 1300 RPM faster than it used to.

My tuner said the idle is set so high due to large intake, throttle body and also even because of my aggressive CAMs. But I think it probably could be set lower now. I might see about that. It might still need to be higher in the winter. It doesn't get that cold here in Houston, but it gets cold enough that it is somewhat more finicky on cold mornings. Maybe I could have a winter tune and summer tune with different idle speeds?

In addition to the honeycomb, I experimented with a different filter. Amsoil got out of the performance air filter business years ago. But I happen to still have an Amsoil 4.5" air filter. It is 1" shorter than CS's provided AFE filter. But it has an inverted top. I don't know of any other dry filter available with an inverted top. And inside, there is a rubber cone air director. I'm guessing this is probably not significant but I figured I would try it. Tomorrow, I will put the AFE back on and see if I notice any difference.

Bottom line, I was happy with the improvement made so far, whether or not I can get the idle lowered or not.

See pictures below of the honeycomb, and of the Amsoil filter if interested.

 

[Sho]

What cams you have?

I have none of these issues with an HTP 4" intake with no air straightener and kelford 247-C cams with idle at 1000rpm

 

[Speedie6]

What cams you have?

I have none of these issues with an HTP 4" intake with no air straightener and kelford 247-C cams with idle at 1000rpm

I guess I need your tuner! (Or if you tune yourself, I guess I need to hire you.) I have Kelford 247-C. The only other thing I know of that could be a factor is the CS throttle body. One review of it said it impacts idle. But, by itself, I wouldn't think it would be that much different.

 

[Sho]

I guess I need your tuner! (Or if you tune yourself, I guess I need to hire you.) I have Kelford 247-C. The only other thing I know of that could be a factor is the CS throttle body. One review of it said it impacts idle. But, by itself, I wouldn't think it would be that much different.

I tune myself. I also have the cs TB lol

 

[Speedie6]

I tune myself. I also have the cs TB lol

I reviewed your I see you also have the JMF intake manifold and CPE exhaust manifold like I do. I was stunned to see you have a Kozmic downpipe! I'm in Houston, as is Kozmic and they built me a custom DP. And they are also my tuner. I thought I was the only person who had an MS6 with a Kozmic DP. I googled and see that they used to market one for the MS3. But you have an MS6. So, I'm a bit baffled as to what exactly you have. But bottom line is, we have pretty similar builds. You even have the CS strut bar which is pretty rare.

Anyway, this leaves me more confused what my problem is. I'd drive over if you'd be willing to give a hand, but Kentucky is a bit of a drive. I'll give Kozmic this information and see what they have to say. But thanks much!

By the way, how does your car handle cold weather? Mine is a little worse in the winter, but we have pretty mild winters. I figure mine would be undrivable until warmed up if I lived where you live in the winter.

 

[Sho]

If you're going thru kozmic, you're in good hands. I'd imagine Justin (freektune) has his hand in your tune.

The kozmic dp i have is part of one of the edge autosport PTE turbo kits they used to offer back in the day. Cpe exhaust manifold, kozmic dump tube and kozmic down pipe with your choice of PTE Turbo. There's a few of em around, granted ms3 version of the kit was way more popular



I just got this setup back on Monday. So I can't comment on cold weather with the cams.

But. Based on my built motor experience when I had my ms3 and lived up near Cleveland, where negative Temps were normal in the winter, I always warmed it up. And it ran like shit if not allowed to warm up