Rough idle and misfire at cold start

I have started to experience a very rough idle at first startup in morning, after sitting in garage all night. Air temps are around 70F. It flashes right up, but seems to stumble a bit and revs are unstable. Occasionally this sets off a misfire code as well. Once it�s been running for 3-5 mins, all is good and runs fine. Restarting through the day, no problem. Only seems to happen with first start of the day. I did a smoke test, as my first thought was a vacuum leak. Negative, all tight Ran Durametric actual values RPM 916 MAF 23.6 kg/h Hot film voltage MAF 1.37V FRA bank 1 1.08 FRA bank 2 1.03 RKAT bank 1 3.70 % RKAT bank 2 4.13% O2 voltage ahead of cat .86V O2 voltage behind cat .49V Now, something interesting (well, at least to me). When I first hooked up the Durametric for that �first start�, I lost signal. So I turned car immediately off, unplugged, restarted Durametric, then restarted car. Idle was smooth. It certainly didn�t warm up, as it ran about 2 seconds on the first start. All the readings above came from this second start, so unfortunately I don�t have numbers for the initial start (when the issue occurs, and what I was trying to capture). Seems very strange that 2 seconds of running, would make such a difference on the restart, but it seemed to, at least this time. I throw it to the collective wisdom for suggestions. I know almost nothing about the numbers generated, aside from those RKAT numbers looking lean? All this electronics/data stuff makes my head hurt Thanks Joe

Disconnect your mass air sensor and se how it goes it’s sounds to like a faulty sensor

Thanks NYPOWR4, that is next on my list. Trouble is, it won’t do it until tomorrow morning now. I do have a spare MAF that I changed as a precautionary thing a few years ago that I can try as well. edit: I should have also noted that I did try “cleaner” on the MAF the other day. I’m not much a believer, but worth a try. Did nothing.

Generic misfire code or a specific cylinder misfire code? Fuel pressure issue?? Just spitballing here.

OP - Your symptoms also would make me think vacuum at first. From just the info you provide, keep it simple. Try a few of my amateur suggestions before grabbing the flamethrower. You might already have done this, but, to help the troubleshooting� Get back to a baseline: -Have you reset the ECU? You want to do this to allow start injection timing to readapt. -Eyeball all those little vacuum lines again. -Turn key and listen for the throttle body. If you don�t hear the test you may not get the butterfly opening properly at start. -Clean throttle body. -Start engine and hear the secondary air pump operate. If the idle is fluctuating after you reset ECU (normal) add a tiny bit of throttle. I believe the baseline fuel injection is defaulted to lean. -Try one start with a/c off and one with a/c on to see if idle stabilized in either/both ECU program modes. This checks for loss adaptation. Idle with a/c off should be about 1100. -Durametric values for air mass deviations-secondary air and short term fuel trims. I don�t recall if a non-PIWIS has the value for air mass deviation. Once the engine is at stable idle, look at your actual values for fault isolation. Of note, your start air mass appears to be on the higher end of the range for start/idle in that snapshot. Your MAF voltage is correct. Remember the MAF doesn�t really play at idle rpm. If the FRAU (idle or low load) are skewed over time, so will the RKAT adapt percentage. Your stable start idle is only valid after the secondary air quits.

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Generic and specific to one bank...then other bank.

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Thanks for all the ideas! Yup. That�s why I smoked it first. All seems to be tight. No leaks evident. I�ll try the ECU reset. Makes good sense. Throttle body cleaned. I�ll have to get another body to help with hearing throttle body, but good check! Interesting comment on the AC. I did notice, while it was idling smoothly, that turning the AC on and off does change idle, but it seems a bit delayed. Takes a couple of seconds for the change in idle. Maybe normal but I�ve not noticed it before. I know it is faster on my other cars when AC turns on, and engine doesn�t struggle.

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Hi Joe, did you ever resolve the cold start misfire? I have very similar symptom, misfire on cold start after sitting for 24 hours, subsequent starts throughout the day are no issue. If I start it, let it run for 10-15 seconds turn it off and restart there are no misfires. Also noticed doing this abbreviated start and restart process the secondary air pump is no longer running upon the restart. Appreciate your feedback. Thanks

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I tried replacing cam position sensors, but still happened intermittently. I then swapped out the crank position sensor and it hasn�t come back. This crank position sensor seems to have a variety of odd symptoms, as I had another friend whose car wouldn�t rev beyond 3500 rpm, after changing AOS. We hunted figuring a vacuum line or something got knocked off, but to no avail. He then took a total shot in the dark and replaced the crank position sensor and it was magically fixed. I�m not a fan of throwing parts at things but not being able to replicate the failure in the sensor on a bench, makes it very hard to diagnose, and Porschetech3 (Doc) is too far from me to use his magic wand

Removed my crackshaft position sensor, had some debris stuck to the magnet, cleaned it off and reinstalled, solved the cold start misfire. Ordered and installed a new one for peace of mind. Appreciate your quick response. Thanks