I saw a PID that just said long term fuel trim on yours but not on bank 2 I think...this may be total fuel trim (B1+B2) but I did see 12% which is a little high (+or - 10% is OK)...did you feel a misfire ??...the bank 2 sensors were probably not fully heated up and that’s why they were low...I had kept my engine at 3000 RPM for 5 minutes or so to see those numbers on my screen shot...with 12% long terms at 3K it’s either fuel delivery or a dirty MAF sensor..your MAF looks OK at idle but for now I’d use a couple cans of fuel injector cleaner, clean the MAF and see if your plugs are being oil fouled.

 

The O2 sensors are saying add fuel due to a lean condition. Along with reporting misfires in all cylinders suggests a few possibilities.

One is a dirty MAF under-reporting air delivery into the engine, so you have a lean condition that requires fuel trim compensation for proper fuel/air ratio. Unless you have a S/D tune, the PCM initially sets fuel delivery based on MAF reporting air in. Then, the O2 sensors are the feedback loop to validate and/or correct the fuel delivery (fuel trims). A very happy system will show fuel trims both short and long hovering around zero.

The other is the PCV system having a break in one of the external hoses, giving un metered air to the engine.

If were leaky intake gaskets they usually improve their seal when the engine warms up.

A leaky bellows between the MAF and TB

bad TB gasket/loose

Another could be the vacuum lines at the back of the intake, the Brake booster hose, the MAP itself cracked, and the little vacuum line going to the vacuum accumulator.

I’m not hearing exhaust leaks in your video, but look for loose exh manifold bolts.

So add MAF reporting in g/s and MAP pressure so we can check off vacuum leaks. At the end of the day there is possibly more air going in requiring adding of fuel. You could have low fuel rail pressure forcing injector pulse widths wider than normal. It would be unlikely you have all 8 injectors dirty. The thing that sticks out for me is ALL 8 cylinders reporting misfires. That would seem to eliminate coils, plugs, wires the culprit. so the issue will be one common to all 8 cyls.

 

Good info !!...a vacuum leak will manifest itself with fuel trims that are more “positive” at idle but DECREASE under load...ops fuel trims were increasing under load !!...a dirty MAF usually “over reports” airflow (rich condition/negative fuel trims) which I don’t see at idle...yes, I don’t think ALL 8 cylinders are misfiring but I’d like to see a screenshot of the misfires...I can’t remember if I had the OP check MAP sensor KOEO but his MAF looks OK at idle...we may need Bernie Thompson for this diagnosis...LOL !!

 

At the end of the day, we are all ”arm chair quarterbacks”. We depend on the OP’s writing ability, and our interpretation of the inputs of the OP and others. It is easier to have the car in my shop with the diag tools I am comfortable with.

I would probably data-log misfires and see if particular cylinders show a higher misfire rate. None of us have mentioned the Crank position sensor. I wonder if a re-learn, is in order. I certainly would ‘scope it along with spark trace to check if the CPS is effing up timing.

Without a really good scan tool and a PICO scope, this might frustrate the OP enough to start firing the parts cannon.

 

Yes, we are ALL arm chair quarterbacks here...LOL !!...I’d do a relearn if he is experiencing “ghost” misfires but I believe he says he can actually feel them...without a bi directional scan tool and a scope misfires are elusive for a DIY’er !!

 

Misfires are a symptom, not a root cause. i had a CTS-V with the LS2. Developed real misfires. Took forever to conclude the engine mounts were both bad, so the engine would develop lateral accelerations that would affect the crank speed. This caused erroneous signals from the CPS. The only codes was every once in a while a p0300 and a blinking CEL. Shut it off and restart, all good. Finally a buddy noticed the engine was tilted ever so slightly, We changed the mounts, with out thinking it would fix the misfires. After theMM change NEVER misfired once again. I ran the pee out of that car and had fun chasing ‘vettes around the track with it.

 

YES !!...vibrations can most definitely cause a misfire...torque tube couplers, wobbly HB etc...
EXCELLENT video below if you never watched this one !!

 

So back to the OP’s issue. With fuel trims making a greater than 10% correction, That’s too much. When. short terms go up the PCM will increase long terms. It is sort of a proportioning control, but compared to chemical process control cars are pretty basic.

Lazy O2 sensors can lead to fuel trim strategy being off, so it is necessary to really have a good graphical presentation of O2 sensor voltage. Ignoring this can lead to CAT damage, so the OP is well advised to keep chasing this to resolution.

My suggestion is to be patient with redundant inputs from the posters

 

Today my fuel trims are pretty normal at idle. long term bank 1 is 3.5% and bank 2 is 1.18%. Short term is ocellating between -3 and 3%. They did just stabalize at 0 for about a minute then randomly jump back to 5% unstabalized, I don't understand why but they seem fairly normal overall right now.
I can't find mass airflow sensor cleaner, all the shops i called are out except one that sayd they are getting a shipment later tonight so I picked up some throttle bottle cleaner on accident but maybe it will help.
It's still getting random misfires at idle in the diag even with the okay fuel trims. And they are actual misfires, two of my friends are who pointed it out to me, I must not have an ear for it.
The MAP at idle is reading 36.91 to 38 Kpa

 

you can use Brake cleaner for the MAF filament. What year is your car? makes a difference. 97-00 had the IAT separate from the MAF, 01-04 the IAT is in the MAF air tunnel. Have you had the MAF off before? You have to be a little careful. You should have a honey comb (except Z06 or if a previous owner knocked it out). You need to clean the honey comb and the fine wires inside just with a gentle stream of brake clean, NO COMP AIR afterwards!!!!! No mechanical cleaning either.

I re-read some of your posts. You changed all the plugs. Did you change wires too? After owning driving and fixing several C5’s, C6’s Chevy trucks with 5.3, 6.0 and 6.2 LS platform engines, my personal rule of thumb my is if I touch a plug wire with my hand, it gets replaced with new. IT is so easy to F up a plug wire removing it from a plug and not know it. AND ALWAYS PUT Silicone grease in both ends AND make sure the wires click on the plug AND the coil. ALWAYS USE OEM WIRES . 5 VETTES 3 YUKONS, 3 CHEVY TRUCKS IN THE LAST 20 YEARS. In all that time all those miles, only one bad coil pack. Plugs and wires common to fail.

So when you are getting misfires you can pull the primary on coil connector one at a time on individual coil packs looking for change in rpm. Use your scan tool set to show RPM, don’t rely on your feel. Also a spray bottle with salt water solution will show a specific cylinder that is occasionally but not constantly misfiring. due to plug wires. The other thing is lately I have been having trouble with AC Delco plugs. I usually buy from AMAZON, but last two purchases, the porcelain was cracked. I suspect the vendors sub-tier to the Big A are selling Chi-Com knockoffs or rejects from Delco’s Chi-Com factory. Big A has lost my car parts purchases until redeemed.

So, with your fuel trims apparently looking good, give thought to the plug changing episode.

So let’s talk about the scanner you have. Will it data-log PID’s ? PID is parameter Identification. MAF is a PID, for example.
If so, then there is some useful info you can find. For example, if you data log MAF and RPM, revving and holding at say 1000,1500,2000,2500,3000 RPM and measuring MAF you can graph MAP vs RPM. EXcel is great at graphing and most data loggers report a .CSV file. This will be a linear relationship if the MAF is good.

If you can data log, great, we can make a list of PID’s to log The only caveat is the more PIDs you select the longer the sample interval Best to keep it below 5-8 PID’s

 

My car is a 2003 base model.
I have been trying to log the MAF and MAP and RPM all day. I have graph form and data form on the device but no way to transfer it to the computer and I've been trying to figure that out for about an hour. I don't really want to type out 600 numbers from the device to my pc so I only did every 12 of the 240 and here are the graphs I got (20 total data points)

The outlier on the MAF is on immediate deceleration. You can see in the data char to the left, the top value is time = 0 and bottom value is time = 20 and I did stair stepping idle up to 4000 about every 500 rpm increments and then let off the gas at the end back to idle and that generated the outlier.

Also these are the wires I use: https://www.amazon.com/gp/aw/d/B00KUL5FU4?psc=1&ref=ppx_pop_mob_b_asin_ title
I got my plugs from the local chevy dealer, acdelco iridium i assume. And I've had this p0300 since before i replaced the plugs and wires, it's just less frequent now with the new ones. I also put in injector cleaner earlier today with a full tank of gas and tried some throttle body cleaner too. I also tried pulling the fuse #15 (o2 sensors) and it didnt seem to make a difference.

 

I finally got the MAF cleaner and cleaned it and now its reporting 5 g/s (even less) at idle and its misfiring much worse with a noticeably rough idle and on decel from 3k back to idle you can see the hood light flicker.
at idle:
long term fuel trim bank 1 and 2 now 15% and 16% !
short term -3%
at 2k rpm:
lt 20%
st -3 to +3%

then i tried unplugging the maf and the car is stumbling a bit but long term fuel trim bank 1 is 8.24% and bank 2 is 1.18% which seems weird. when i then hold it at 2k rpm it starts to even out to 0% for both from what I can tell or maybe -1.96%

Cylinder 3 does seem to be thr biggest offender of misfires, with the other odd numbered ones next then the even ones.

 

You may have a vacuum leak...your fuel trims were OK prior to cleaning your MAF...you can verify by keeping your RPM at 3000 and watch those long term fuel trims...they will slowly decrease as RPM is increased...since you cleaned the MAF recheck the rubber bellows ends between the MAF and throttle body or the clamp at the MAF on the downstream side...it may not be installed correctly...it happens a lot here !!..you should concentrate on #3 cylinder if that one shows the most counts !!...if that one shows 50 and the others 5 or 10 concentrate on #3...you can try to verify with a “cylinder drop check” but verifying on a V8 engine is difficult...to rule out a mechanical issue you can do a clear flood crank(hold gas petal to floor and leave it there) and then start the car...injectors will not fire so car will not start...listen if the engine has an even sounding cadence as you crank... I had a C6 member try this 2 weeks ago who had a misfire and he could hear the engine speed up and slow down during cranking..he had a mechanical issue which turned out to be a broken rocker pedestal bolt...you can start here.

 

Great job graphing work!. It looks like you had a very good result before cleaning. Don’t worry about the deceleration graph; the second one. The top graph, ignore the outlying data points. That is probably a sampling interval issue and perfectly normal foe there to be an instantaneous spurious datum. The MAFvsRPM looks very linear GOOD. So, if the conditions after cleaning did not change, then MAF may be ruled out. C5 Diag is spot on regarding vacuum leaks, so let’s see if you caused one during disassembly. I like to put silicone grease, a very light coating on the inside of the bellows between MAF and TB in the area that seats on metal. A quick check for vacuum leaks is to spray a SMALL amount of brake cleaner or your TB/MAF cleaner at suspected vacuum leak locations. Best done on a cold engine. If the engine immediately speeds up, you have found the vacuum leak. The cleaner is a fuel and so you are adding fuel and air (the leak). The engine should briefly increase RPM until it sucks in all the cleaner.

I noted in a previous post several vacuum leak sources. Cyl 3 might be an intake gasket. Wouldn’t be any harm checking torque on the intake plenum bolts, especially around #3 BTW, 1357 cyls are driver side (bank 1) 2,4,6,8 passenger side (bank 2)

 

Your car has been running badly for awhile and the adaptive data is probably all screwed up due to the misfiring and now the cleaning of the MAF. I would disconnect the battery for awhile to reset everything to defaults. Then look again at whats happening with the fuel trims and MAF data.

 

Well funny you say the area between the maf and tb because it has looked like this since i purchased it:


So this spot is the top side that clamps onto the metal throttle body. I don't know what happened, but the previous owner didn't take good care of the car. What's this part called? I'll try to order a new one.

 

Air bridge GM 25314823

 

Okay thanks for the part #!

also here is a vid of me cranking the car:
and now that the maf has sat overnight it's reading 6.5 to 7.0 again which was the same as before cleaning.

Another thing worth noting is that in park and neutral the rpms are about 100 to 200 more than reverse and drive at idle. If i hold the brake down while in drive at idle i get significantly less misfires than park or neutral at idle. Almost 0 misfires in drive. Also oddly it gets more airflow when in drive (lower rpm) than in neutral (higher rpm).
here:
drive:
550 rpm
6.9-7.5g/s
neutral:
630 rpm
6.5-6.8 g/s

that is clearly not correct. I think it should be getting more air in neutral and park right?

 

The poster above has the name. You probably won’t find a new one. Lots of them around, as many have replaced the intake/air cleaner with “cold air” intakes. Waste of money.

You will have to go to a Corvette salvage to get one. You need the 01-04 version, not the 97-00 version. Marc Rose at Vettenuts is a forum vendor. His business is in Bedford County TN . Then VettePros in Charlotte NC 704-320-0073. You may find an air bridge in the C5 parts for sale section too.

That is a good find on your part. That connection has to be air tight. That is a source of un-metered air. and for sure a source of varying change. The engine will rock a bit when you wind it up and this will open for more air. Fixing this will calm the engine variations so trouble shooting can finish. This would be a very frustrating condition. No wonder you are having a fit with this!

 

So the MAF air at idle usually is closer to 5.7. Idle RPM may be a bit high which can’t be established until all air leaks are resolved. You may have a dirty throttle body.