Idle Issues
 

Hello, tuning noob here. I have a yr 2000 nb with MSPNP2 and have been having idle trouble for a few weeks now. The car idles (mostly) fine when it's warming up, sometimes stalling on cold starts, but when the coolant gets hot and oil gets to 180 or so, it goes really lean and starts jumping around. If I hold my foot on the gas to try and keep it steady, it'll dip every few seconds then rise back to the RPM I'm keeping it at. It stalls quite often unless I can rev it to keep it going. Using the AC during idle immediately kills it. I have the AC idleup enabled but it doesn't seem to be doing anything. Could be totally wrong but I feel like the outside air temp has something to do with it. It idles much better and richer early in the morning and late at night. Mechanically the car is really solid but I'm just looking for a second opinion on the tune to try and sort it out. Any help would be greatly appreciated.

EGO is disabled, which obviously doesn't help controlling AFR at idle. You do have MAT air density correction pulling around 5-10% depending on air temps, do you have a log of it idling? The initial value table doesn't look like it's tuned very well, but if you're idling around 32.9% DC, it might be ok.

Here's a log of the car idling and getting up to operating temp. I turned on the AC and blipped the throttle a couple of times to show the effect, and the final time turning on the AC stalled the car.

Your VE at idle is 72, injector dead time and voltage correction is correct, and that results in ~16.8 AFR once WUE is off, and before it starts oscillating like crazy, most likely from running lean. Your target AFR is 14.7. Simple math of 16.8/14.7 is 1.14, so you need 14% more fuel at idle, 72*1.14 is 82, which is crazy high for idle VE, should be in the 20s or 30s, maybe 40s. I would be willing to bet you have a fuel pressure issue or injector install issue.

Try the attached tune, it has a number of fueling changing to help you correct idle, load it and take another log at idle.

I really appreciate the help and explanation. Took a log just now and noticed a slight difference, but it returned to the same sputtering after pressing the gas. The fuel pump is stock which might be the culprit.

Main relay can become carboned up at the contacts and make resistance, too. It can degrade the performance of the fuel pump semi-irregularly as it is slightly different resistance each time.

Or 30 year old fuel pump is 30 years old, or however old yours is.

I still think you have something weird going on with fueling, but I'll keep entertaining this as long as its....entertaining.

You have cyclic fuel cut every ~25 seconds (before your major idle oscillation) that I can't figure out. It looks like over run fuel cut, but you haven't met the parameters? It's right after you reach the temp min of 175*, and you're idling below the min map of 30, but you're below the min RPM of 1500. Anyways, here's another tune with over run fuel cut disabled, and a huge smoothing of the fuel table. Don't do anything but idle with this tune.

I'm glad I could present a challenge at the very least. And in any case it seems to be idling much better now. I also checked the main relay and there was no sign of any corrosion. Not sure if I still have a fuel issue but from my limited point of view it seemed better. Now I just need to make this tune driveable.

So it's idling most of that time at 85%, so it's pulling 15% fuel. So you could take the idle region and multiply by 0.85, ending around 70-71VE, which is still high, but better than 82. EGO is deactivating due to MAP min of 20kpa, which is some crazy good vacuum btw, so you might drop that down to 15kpa. IIRC FF640s have some weird VE numbers, but it's been a bit since I've tuned a set. IIRC the difference between idle and WOT on naturally aspirated cars was surprisingly small for whatever reason, but double check your fuel pressure is within spec first.

Just threw a DW 200 in there. Going to check fuel pressure and see if that changes things.