Alright this is driving me nuts.

I'm getting a sporadic ignition issue. It seems to be getting progressively worse. First time I noticed it as a slight miss while cruising at constant throttle, which happened once or twice on a two-hour drive. A few days later at a stoplight, the idle started to stumble, went from a smooth 900rpm to a rough 500-600rpm, a/f goes from ~12.5 to around 10.5. It usually only lasts about 5-10 seconds and then goes back to normal.

Recently it has gotten really bad, the idle will stumble randomly every few minutes. Usually it stays running by itself, but it has died a few times, the idle just keeps dropping and stumbling until it shuts-down. If I blip the gas when it's stumbling it hesitates a few times and then revs smoothly.

It also does this while cruising, which is the worst, all of a sudden I'll just lose all power but the RPMs don't really drop (which makes me think the leading coil is randomly not firing and the trailing is barely keeping the motor running). A/F goes really rich and I get pops in the exhaust like a 2-step if I keep on the gas. Car is pretty much undrivable because of this, it happens so often.

When it goes away after a few seconds, the car pulls super hard and idles smooth like it should. I replaced the plugs today because they were pretty carbon fouled, but new ones didn't make a difference.

I'm wondering if this could be a wiring/ground issue? CAS signal? I've gone through the wiring and connections and haven't found anything suspicious, but I could be missing something.

It was running perfect for the past few months since the Haltech was installed, prior to this issue. So I don't think there is anything wrong with the maps. Some details:

-S4 13BT swapped into a 1st gen (motor has ~35k on it)
-Bare bones, no emissions or BAC
-Haltech E11V2 (red), stock FC ignition set-up, Haltech TPS
-New plug wires, brand new plugs
-Checked grounds
-CAS wiring is as far away from plug wires/alternator as possible
-Doesn't seem to happen until the car is warm (but it's random)
-Coils don't feel hot after driving (haven't checked resistance though)
-Good vacuum (18-19in.Hg at idle)

Any suggestions? Thanks guys.

 

The mystery continues. I was messing with it again today, hitting areas with contact cleaner. I started it up and it stumbled once briefly, then idled solid for a good 15 minutes. Shut it off and started it up 3 times, trying to get it to stumble again, and it stayed solid. So I go for a quick trip to the gas station, and it sputtered and died out of nowhere before I could get out of my neighborhood. So I turned around and parked it, then just let it idle for a good 10 minutes to see it the problem would pop up again. Nothing. Idle stayed rock solid. Which is making this really hard to diagnose.

Could it be a faulty sensor? I'm not sure if any of them would cause a problem like this. The CLT/IAT/TPS/MAP sensors were all brand new from Haltech when it was installed.

I guess I should note that I'm not getting any dimming or flickering lights when this happens, so I don't think the charging system is suspect.