That’s it.
He is trying to fix the misfire - Carbon build up can cause misfire.
I am now a hostage! I do not what should be my communication strategy? M/c seems a believer of Carbon to misfire as he stated it to my partner when she took the car there. But he did not perform but found other issues. Customers say he is honest - I do not think that a human will be 100% honest.
He seems the best in town and the Honda specialist - negative review seems about communication - he also has about 2-4 wks of waiting before he can attend to your car. The shop I used to go is closed - he was an awesome m/c and fast.
This is the first mention of misfire. If you want help with this, give us more info about the circumstances and symptoms of misfire.
Some old Hondas/Acuras with distributors develop some play in the shaft. There is also an electromagnetic pickup in there - like a crankshaft position sensor. Those can interrupt the ignition, especially when hot, when they start to fail. How’s the cap and rotor, if present?
Current state:
M/c fixed the vacuum leak. Lean condition became Rich condition that he is investigating now. I tried to suggest that the computer needs to re-learn! He also did not test fuel pressure.
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:
LTFT - 4.6
STFT - 7.8 - 12.5
Originally:
- idle random misfire P0300, P0304 and occasionally P0303
- Changed spark/ front O2 sensor (OEM) - Spark is platinum a level up from OEM
- Changed cap/rotor, spark wires with aftermarket parts - still misfire
- Swapped the Dizzy coil but still misfires
- Engine compartment is dry except Dizzy neeeded a new O ring - took care
- Compression was good 175 to 190 (renage 135 to 199)
- M/c did the leak down test and no issues
- I added S1 fuel injector cleaner and the car started running fine (for a day!) but then misfiring closer to 2400rpm on road and not on P gear. Misfires on all Cylinders. Basically it misfires at idle and stops once warmed up. But on the road, it misfired around 2400rpm.
- Owned the car for over 15yrs with little issues.Last yr IACV had to be cleaned. Carbon build up stopped its functions temp - after cleaning it started running like a new car. Throttle body is clean.
- Use Mobil 1 5W30 every 5k.
- valves adjusted 22k miles ago
- air filter has 8k
- Spark plugs did not show any abnormality
- Batt and Alternator tested fine
- cold start gives gas smell through exhaust even before the misfire
- only known issue is the car would need jump start if you don’t drive for 2 weeks
Related thread:
https://community.cartalk.com/t/are-the-cap-rotor-still-good/175532
Update:
I did edit here and there and added new info.
I found a review saying “I have been using it for many years. I put 4oz. in a full tank of gas every 4th of 5th fill up. I always start a long road trip with a treated tank of gas. It cleans up the valves & valve guides and it also frees up the piston rings and fuel injectors.”
He puts 4oz. the bottle is 32oz. Does this mean, whole bottle can harm?
https://www.oreillyauto.com/detail/c/marvel-mystery-oil/marvel-mystery-oil-top-cylinder-lubricant-1-quart/mvl0/mm13r?
Slow and steady. IIRC 4 oz. per 10 gallons or per tank - whatever the instructions on the product said, that’s what I did. I think every tank, once I started with it, for a year or more.
Didn’t this misfire problem begin after you performed your ignition system maintenance?
Ignition system maintenance was only initiated after the misfire (rotor/cap …).
Another m/c wanted me to change the Sparks and Wires before he diagnose.
I have been using MMO for many years in every vehicile I owned. I put one bottle in a full fuel tank and one in the crankcase twice a year don’t know if it did any good but it did not hurt any thing.
Just to toss some ideas of the potential root cause…
Timing chain/belt stretched or jumped a tooth?
Valves getting tad-bit too tight, enough to give OK-ish compression reading, but failing under higher RPMs?
Worn camshafts, having timing out of spec?
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Nothing to add . Will check back when this reaches 100 posts.
All valid points - took note of them.
Tightening valves - is this something mechanics will hear right away?
Also, not all can be diagnosed - eg one guy had his ignition coil passing the test using volt meter but when he swapped, it fixed the misfire.
M/C has not gotten to the fuel system when I spoke last - I raised the issues from this thread. Similar scenario - I spoke to the m/c about it but he is meticulous so I need to wait - m/c only spoke about one gasket on the FI (but there are 3) - apparently the gasket on FI were bad + CAT?
https://www.acuraworld.com/threads/cylinders-1-4-misfire-tried-everything.91148/page-1
that’s a problem you DO NOT hear 
I bet the engine would have valve cover easy enough to open and checking the clearance would be relatively easy to do to check this problem out
fuel rail pressure must be another good thing to check
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The first thing I would do is replace all the aftermarket ignition pieces with OEM. Japanese cars are notoriously sensitive to aftermarket ignition parts and often run like junk when using them. I KNOW that the problem preceded the parts replacement, but I would start there. Once you are running OEM components (including spark plugs) in the ignition, see what kind of result you get.
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I was told the same working on 15-years-old Nissan… and number of shiny non-OEM parts were needlessly replaced… only to underline that the root cause is “somewhere else” 
I would say part swap is not a substitute to diagnostics
-
Misfire
One of the 4 injector was bad (but passed ohm test)
Replaced all 4 with reman injectors and the misfire is gone -
IACV & Vacuum leak
- Last yr Idle Air control was clogged with carbon giving P0505
When the AC service was done they said AC would not work at idle due to IACV. Two shops said cleaning will not work. I cleaned and all issues gone. - This time shop found a vacuum leak since I did not change the gasket. He changed the gasket and the car developed P0171 at idle.
- P0171
– When the car is idling, the STFT slowly creeps up and the car earns the P0171 CEL at idle
When driving steadily, CEL goes off.
The car has no drivevability issue.
Fuel pressure and regulator were tested fine.
Shop tells me that the next thing in their manual is Valve adjustment.
Shop also told me the Scanner shows less responsive (new) O2 sensor! Is this ECM or wiring? ECM is not common on this car.
I am wondering what is causing P0171 at idle? IACV, … ECM, Valves adjustment, Leak, something else? Shop did not have a Smoke machine.
Update:
Past LTFT was about 6 and STFT was about 8. After the Vacuum leak repair, LTFT goes to 19 or so at idle and comes down to 14 when driving.
Should I re-introduce the leak at IACV and see if the CEL goes away?
IMO there’s still a vacuum leak.
Try pinching off the brake booster and EVAP vacuum lines while idling.
@circuitsmith - will do so.
It appears to me that this was introduced in the shop since LTFT is way high compared to when I took it to the shop. It might have been because of the age of the car. Car is very clean.
So when I pinch, what should I expect to confirm a leak or no leak?
Watch for change in fuel trims.