Check engine light came on about a week ago.Purchased code reader, P0150 and P0130 came on same time. car still ran fine. After a few days noticed rough idle and later ignition misfire.
Code P0300, 301, 305, 306, Changedspark plugs at 150K approx 5k ago regular maintenance.
New air filter. oil is changed every 5K.
Removed EGR valve today and cleaned pipe and throttle plate and checked for vacuum leaks.
After start more engine misfire. Removed spark plugs #1 and #5. Showed definite signs of rich mixture (black fouling)
I suspect the O2 sensors are reporting the correct information. I am not sure the OBDII reader is able to report MAF errors (Innova 1003C) although I has P0100 etc explanations.
Hard for me to reason that both sensors failed at the same time I also had one report of code P0136 did not reappear after clearing code.

 

inspected the fitting between the maf and the intake tubing?Changed your fuel filter?Ran out of gas lately?Checked the wires to the two pre cat sensors that the codes indicate?Rats love to eat those wires.did you unplug the maf and run the car on open loop and see if the misfire codes come back?Make sure the plug for the maf is fully seated.
ohlord
what oil are you using? Mobil 1 0w40 syn is mb spec and with fleece filter lasts 10000-12000 miles on the fss system.Why are you changing it so often?

 

ohlord has beaten me to it including the 5k oil changing bit.

Not familiar with your code reader and whether it has live data capability.
However the codes indicate BOTH O2 sensor CIRCUITS but I'm of the view that O2 sensors are very reliable UNLESS they have been contaminated by some agent.

What you really need is to have a look at the O2 SENSOR WAVEFORM. I.E. VOLTAGE AND CYCLING FREQUENCY. MAYBE YOUR SCANNER DOESN'T SUPPORT THIS.
OOPS . SORRY ABOUT CAPS.

Suggestion. Reset codes and start engine. Does CEL come on straight away.
Yes. What are the codes?
No. Go for a run (in the car) around the block.
CEL ON?
Get a pattern of codes versus operation from cancel to reappear.

Now if all was OK before you started investigating and using your scanner what exactly did you do?
You didn't have an obvious misfire at the beginning. You did at the end. So what did you do? Remove air filter, plug leads etc etc.

When did you last fill up....Contaminated fuel?

Stuart

 

I change oil frequently because its the cheapest thing I can do for a long
running engine.

I removed and cleaned the whole input air passage form the filter to the
throttle plate. It was not dirty.
This problem stated slowly with the check engine light coming on and after a
few drive cycles it would self extinguish.
no noticeable change in engine performance.
checked and reseated all O2 sensor connectors as well as the MAF.

next dayI started to notice a slight misfire usually associated with fuel air
imbalance ( only at idle). this got worse over a few days that the engine
started to report multiple cylinder misfires.

The exhaust is spitting black water now at start up due to ritch mixture.
First noticed check engine light at 1/4 tank . Car has not been run with the
tank low enough for fill up light to come on.
The fuel filter has not bee changed. No damage to the wires and I keep the
engine area clean.
I was not aware that the car can be run with the MAF disconnected.
The sensor has not been tampered with or cleaned. I know how sensitive they
are.

I am worried that if I continue to run the car I will destroy the CAT
converter.
Are there any other components that regulate air fuel ratio besides the MAF
and O2 sensors.
Car runs rough even though it is operating in open loop (engine cold).

I have changed the gas and even added sure to pass emission reducing engine cleaner.
The spark plug misfire is happening due to the plugs fouling from the rich mixture I am fairly sure.

 

Crank sensor,cam sensor,and coolant temp sensor all also help regulate ignition and fuel injection.Misses on both sides so you can rule out a leaking head gasket.clogged fuel filter will cause misfires and throw a lot of codes you would normally not think it could.
Don't throw parts at it might be time to get it on a real time scope and find out what is failing and causing the problem and then you fix it yourself and just pay for the diagnostics.
ohlord
using mobil 1 0w40 syn mb spec and fleece filter every 10k miles per the fss is the cheapest thing you can do for a long life engine doing 20 oil changes over 100k miles will give you no less wear and toss out a grand of oil and filters that did not need to be tossed out[:-]

 

O2 sensor driver side bad created rich fuel condition, Al other misfire codes and plug fouling as a result of failed sensor. Replaced all four. runs like a watch again.