Random misfire on Acura – and seems mysterious

1999 Integra LS with 144k miles and Auto, B18B1 – no mods
Well maintained. Due to the random misfire at idle (car shakes too), did the following still an issue:
P0300, P0304 and at times P0303 – now all cylinders
– sparks (OEM), wires (after market)
– front O2 sensor (OEM)
– cap & rotors
– valves adjusted 22k miles ago
– air filter has 8k
– cleaned IACV
– Compression were from 175 to 190
– Spark plugs did not show any abnormality
– Swapped ignition coil but no change
– Batt and Alternator tested fine
– cold start gave gas smell through exhaust
– at times smelt gas under the hood but no sign of leaks
– engine compartment is mostly dry – needed to put new O-ring on Dizzy – the issue started before this repair
– Lately idle misfire goes away when warms up but happens at 2500rom – then misfires on all Cyl
– only known issue is the car would need jump start if you don’t drive for 2 weeks & high NOx

Fuel Trim:
Originally:
1500 rpm 2500 rpm
LTFT 6.2 6.2
STFT 6.2 8.6

After I disconnected the battery and let all the Capacitors discharge at idle:
LTFT – 4.6 4.6
STFT – 7.8 – 12.5

Had the car for more than 10 yrs.
Any help? How can I get Eric to reply?

Can 87 vs 91 gas or additives cause misfire?

• This topic was modified 2 years ago by  .
• This topic was modified 2 years ago by  .

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[ms2000Participant]

My car passed SMOG despite the potential of P0171 at idle:
Test 2021-Final → 2021 (prior 2 tests)
15mph 81 → 357-> 578 (from highest 578 to 81)
25mph 44 → 1079-> 639 (from highest 1079 to 44)

This is a 1999 with 144k miles. Emission levels are amazing! These are better than what I had 10yrs ago.
I still have to figure the Fuel Trim maxing out on idle! I was going to change the IAC but saw some improvement (unsure its lasting improvement) so instead went for the SMOG. I will be pursuing a diagnosis.

[Author]

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