Bri Bro

I ran that exact same setup without any idle issues. The only thing I had to do was adjust the AFR with the MAFblaster in some cells. If it was a transfer function in the MAX DME chip, we all would have had idle issues.

brrgrr

I checked TPS, idle set screw, vacuum leaks - all ok.

I sprayed some cleaner into the ISV.

I adjusted the curve in Mafterburner - basically leaned it out a little in the area just off idle. My theory being the car was getting too much fuel as the MAF drifted back to idle.

It is better - the car won't stall, but it comes close. If I am accelerating and then have to get off the gas and depress the clutch, the RPM will fall to "Zero" and then bounce a few times before settling down to idle.

MZMAN - you have a PM.

mzman

I will keep updating till I have at least made the issue more liveable, hopefully we can come up with some what of a solution.

Excellent information thank you for your help in this. I am with you I think I am going to see what I can do with the setup now. If worst comes to worst I may convert back to stock AFM.

I have a modified 1-series M now for my go fast kicks so don't feel like spending a ton on a Vitesse setup like I wanted when this problem came up a year or so ago.

Lean out some lower idle cells I am guessing? I'd be interested in getting your tune or a screen cap of your tune for idle if your willing to share.

Good to see you are making some progress, I hope to try all of these ideas this weekend if my shop doesn't get blown away in all of this bad weather coming. Checking my PM now.


It is so refreshing to come back to rennlist after being over in bimmer world for a little while. BF.C, e90post, 1addicts, etc. the quality of users and expertise here is far above anything you can get over there.

shortyboy

hows the condition of your blow-off valve?check if the diaphram is damaged.aare your venting to atmosphere?that could cause the same issue,because I am experiencing this issue after each full WOT, then letting off the gas, my tach needle would goto 0 and sometimes go back to normal idle but usuall dies.Ill also be checking my ISV and vac. leaks, though im pulling 16+ -mmHg at idle.

Tom M'Guinn

I’ve struggled with this several times. You definitely need to confirm all the basics are good – TPS, ISV, Base Idle, vacuum leaks, grounds, temp sensors, etc. What usually happens is that the MAF signal voltage is remaining too high when the rpms get to idle speed, and the motor is flooding as a result. Normally, at idle, the MAF signal voltage (as measured on pin 7 of the DME) is around half a volt, plus or minus. When you floor it and let off, the voltage needs to go from whatever it was (say 2 volts) down to half a volt or so before the rpms drop to idle and the injectors kick back on. Normally, this isn’t a problem as most MAFs react quickly. However, if you have a vacuum leak, it will act much like a blow off valve vented to the atmosphere – i.e., it will throw off the air fuel ratio because the MAF is measuring more air than ever makes it to the cylinders and as a result the DME will deliver too much fuel. Also, if the MAF is too close to the bypass valve (or turbo) or you clock the MAF in the wrong way, the bypass air (or turbo) can create a windstorm in the MAF and generate a mistakenly high voltage. Early MAFs were notorious for this. Speedforce racing made an early name for itself by figuring out to move the MAF further away from the bypass valve. You can test all this by watching the voltage on pin 7 of the DME via datalogging or a friend with a multimeter in the passenger seat. If you floor it and let off at low RPMs, you will probably see the voltage remaining too high (e.g. twice your steady-state idle voltage) when the RPMs come down to idle speed. If your fuel controller has the granularity, you can mask the issue by strategically taking lots of fuel out under and around where it idles (but preserving the normal idle itself). As for a real cure, every time this has happened to me, it’s either been a vacuum leak (even though I would have sworn on a stack of bibles I had none) and/or a base idle set too low.
So here’s what I’d suggest. First triple check all the basics. Then check again for vacuum leaks – pull the I/c couples off and bend them in your hands looking for slits that might open under pressure, etc. If that’s fine, then I’d set the base idle (the screw on top of the throttle body) as high as you can while still allowing the system to return it to 840+/- when warm. If you still have the issue, try clocking the MAF differently and/or extending it as far away from the bypass valve and turbo as possible. If none of that works, chuck it and buy a Vitesse MAF.

Tom M'Guinn

Pulling up this thread to see how many others have this issue? Having seen it too many times, I now have a foolproof hardware solution, but curious if it's even relevant still in our modern MAF world...?

Black51

No issues with M-Tune here.

jmj951

I have this exact same idle issue. Although I have a Vitesse MAF, this started occurring about two years after the conversion. It popped up the last two months that I was in the U.S. and didn't have time to work on it, so I just 'drove around it' like a previous poster described, driving down through the gears until I came to a stop so that the idle did not drop quickly and kill it. I won't be able to troubleshoot this until December. I have a WB, but I don't recall exactly what it was reading when it died, I was too busy trying to 'catch' it with the accelerator.

mzman

I followed all of the suggestions in here and upping the idle was the only thing that helped a little. I'd be interested in a hardware solution, but also thinking about going to a M-Tune maf setup and ditching all of this.

Would be interested in seeing what your hardware was.

lart951

i have the same issue with the 2nd gen lartmobile

Brian Morris

If there's not an underlying issue like vacuum leak etc, this can be fixed easily by changing a parameter in the software. When the tps goes to idle and the rpm is above a certain rpm the dme turns the injectors off, lets the rpm drop, then it turns them on at a certain rpm to "catch" the engine before it dies. The "turn on" rpm is easily set on the chip. People also have this problem with lightweight flywheels. Whoever made your chips should be able to easily fix this for you (if there isn't some other problem).

Tom M'Guinn

Here's a picture -- it's another Arduino project Put simply, it just clips the MAF voltage to an idle-friendly limit anytime the TPS throttle switch is closed. (The Arduino is overkill for this purpose, but it can also double as a fuel controller this way.) The traditional reason MAFs fall through the idle is that the MAF voltage is not returning to idle levels fast enough after heavy load. For example, assume the MAF voltage is normally .65 volts at idle. When you floor it, the voltage goes up, but then has to come back down quickly if you let off the gas and push in the clutch. With the turbo still spinning and the blow off valve blasting air in the j-boot, there is lots of frantic air moving around to confuse the MAF and make it read too high. That's why clocking the MAF and moving it further away from the turbo (like SFR did a decade ago) seems to help. If you log pin 7 of the DME you can confirm it -- the voltage will stay up over 1 volt even though the rpms are down to 840, and as a result the engine is overly rich and either stumbles until the voltage comes down or just dies. By clipping the voltage to a reasonable upper limit whenever the TPS throttle switch is closed, the motor drops right back to idle speed without risk of dying.

Dougs951S

Elegant Tom. I enjoy reading about what you do with the Arduino boards, and this is no different. Could a trim pot be added to this and used to control fuel globals?

Tom M'Guinn

Thanks, and yes, it can easily provide global fuel adjustments, but because it's all software based, it can also adjust fuel based on any input desired -- rpm, engine temp, manifold pressure, time of since start up, extra tip-in, time of day, you name it... I'm going to get started on timing adjustments for a more complete piggyback -- stay tuned.

Dougs951S

I'm staying tuned to this. I'm on a bit of a personal mission to see how far I can push the AFM. Mine is ported to hell and back and I'm interested in using something like this to add fuel based on a MAP reading to compensate for the MAP levels which exceed the AFM's ability to control fueling. I spoke with Joshua a while ago and he told he could accomplish the same thing on chip, but that it would of course be an iterative process to get the variables correct. Something like this would make it easy to keep twisting a dial ( simplifying it I know ) to get my fueling correct. I think a true 400 rwhp is doable with an AFM-MAP tune.