Getting plenty of misfires only at idle

[Ludeem1]

This started recently, my gas tank was almost empty when I started to feel a misfire through the steering wheel, I figured it was because my gas tank started to get low. I put about more than half a tank and still the same. It’s been getting a bit worse. I check the gap on my spark plugs and they are all gapped correctly, also put back my stock coil packs, have whoosh ones and same issue. I work about 15 min away all street driving, all stop signs. I’m monitoring misfire count and on the way home today I only got one misfire, but as soon as I got home and let it idle the misfire count climbed pretty fast. Been sitting here about 10 minutes and misfire count is at 56. Idle is kinda rough compared to how it was last week. No codes yet. I’m thinking evap harness. Car isn’t misfiring under load and doesn’t seem low on power. Car has 67k. Car has an S280. Any ideas ?

 

[Ludeem1]

https://youtube.com/shorts/vy-9ztuR9oc?si=h_-_KVjFiLwRWRFC

 

[Ludeem1]

I did a compression check, engine was stone cold. 120 PSI all across. Weird the misfires stop when the ac is turned on and the idle climbs.

 

[TyphoonFiST]

Is the check engine light on?

 

[Ludeem1]

Is the check engine light on?

No codes, once this tank of gas empties I will try another station. The 76 I put gas at always seems to do weird stuff. Last time my OAR went to -0.98 after a few hard pulls

 

[TyphoonFiST]

Then you didnt meet Fomoco threshold for illuminating the MIL light with the Ign. system.If you have access to e85 put a gallon in with your next fillup. Then check the Misfire counter.

 

[Mega ST]

I have the same issue. It's itermitten though. If I fill up it's very hard to start. Have to do the EVAP line fix.

 

[Ludeem1]

I been wanting to the the evap line fix for a while now and pulled the trigger. Didn’t fix the problem. But today I had about 1/4 of a tank left, added a bottle of Techron to the tank and let it idle for a bit. No luck. Decided to put in about 2 more gallons of gas from another station, current gas I have is 76, decided to put shell as i always do , the misfires completely went away after 2 miles of driving. Got home and let it idle for about 20 minutes, not a single misfire. I might of gotten maybe a bad batch of gas. Even though my OAR read -1.0.

 

[Mega ST]

Probably because you didn't have the code indicating something else was going on. I have the P1450 code which def indicates an issue with the EVAP system. Also had a P2196 B1 S1 O2 code and had to replace that today. AFR was frozen at 14.70 and car ran like crap. One weird symptom when the system can't bleed pressure is the fuel gauge creeps upward and sometimes the fuel pump will wine or some noise comes from the tank. A P2282 code popped up last week too. Hope thats related to the EVAP issue or I'll have to track down a leak somewhere.

 

[Ludeem1]

So the issue did come back. Determined it wasn’t the fuel. The misfires are pretty bad now, only at idle. If A/C is turned on the misfires stop. I’m thinking maybe a vacuum leak. Still No CEL.