SOLVED: 3rd gen 4cyl misfire

Hey, new member here.
Okay, we have a 1998 4runner, 2wd, 4cylinder with misfire codes on multiple cylinders.
Before the misfire we replaced the pcv valve to get rid of really odd sound, that worked.Car drove fine for an 8 hour round trip and then sat for a day, then it had the misfire.
Facts: engine shakes a bit at idle, at 1000-2000 rpm shakes, above 2500 it smooths out and drives 'ok' and check engine then flashes.
New Plugs did not fix it or change anything, in fact all 4 of the new plugs fouled very fast and are black and smell of gas and are wet.
MAF clean, air filter clean, spark seems present since i can drive it fine above 2500 rpm, switched a few spark plug cables but it made no difference.
so my question is since all 4 plugs are wet and fouled are they causing the misfire or are they getting wet and fouled because of the misfire?
How do I determine burnt valves?( a known issue with these I have read and no engine work has ever been done to this car, only new alternators and radiator and tune ups. its been best car i have ever owned hands down in my 54 years)
No obvious signs of bad head gasket.
I was thinking of buying a cheap compression tester, if bad compression then I will sell/scrap the car because t has lots of issues, no PS,AC, bad tires, rear brakes, 275k and just not worth fixing if the head or valves need work).
I want to do this DIY but most of my skills are with volvo 240's and those are so simple anyone can fix them. if i can fix misfire on my own (cheap) I will keep car and slowly fix all the other known issues like PS, brakes, tires, and keep it on the road.
bascially looking for advice to help determine if i have a keep or sell situation.

 

First of all. Post the codes. Then clear the codes. Then when they come back see if they are the same.

I think you should do BOTH a compression and leak down test on all cylinders.

Second, when it's running, if you have a code reader that will do live data, see what the ECU is trying to do. What are the fuel trims? If the ECU is really trying to add too much fuel, you may have bad O2 sensors or a bad MAF or both. The ECU does only what the sensors are telling it.

If ALL the plugs are wet with too much gas, then a few things come to mind:

Bad fuel regulator. It can cause a rich condition. -> https://www.carparts.com/blog/the-top-5-symptoms-of-a-bad-fuel-pressure-regulator
Bad ignition system. This might mean the ECU since we're talking all 4 plugs fouling. You may want to swap coil packs just to see if something changed. I would also check all wiring for bad connections and grounds.

 

A plug can become fouled because of a misfire, and a misfire can cause fouled plugs.

For example low compression leads to incomplete or no combustion so they get dirty with unburnt fuel. While a scenario like a bad fuel injector can cause it to become fouled then misfire. Both are possible.

Even if it isn't burnt valve you should adjust it asap. The compression test will tell you all you need to know, if it's low it doesn't matter if it's a valve or something else because I don't think I'd repair it unless it were sentimental. If it is low you can add a little oil into the cylinders, and if compression goes up you know it's not the rings. Rings rarely go bad on these. Whatever you do don't cheap out on a compression tester, the hose will brake loose and spin and now it's stuck in the spark plug tube. I've done it

All 4 plugs being foul is a good sign, these major problems normally affect 1 or 2 cylinders, not all 4

 

@negusm and @Trekker
Thanks, very helpful information. I will report back after I do some more tests. fingers crossed.

 

@negusm and @Trekker and anyone else.
Ran compression test today and had 182,182,183,182.when test was done as final numbers, i could see need jump to 190 while cranking.
Test was run as follows: ran car to operating temp, removed all plugs, removed EFI relay, unplugged power to coil packs.
Only odd thing was during test of #2 cylinder it had a loud scrape, skreech sound but still had good compression?
I think I did test right(first time). So is it safe to assume good compression means no burnt valves or worn pistons?

Code is currently just 301, but i cleared them awhile back and had a 302,304 and 300.

Not sure what to try next w/out throwing parts cannon at it. any ideas are welcome before i limp it to local indy shop 4 miles away.

If i can at least fix the missfire I can sell it for a little more money and someone else can bring her back unless i keep it and slowly do all that(since i dont need the car but is somewhat sentimental (but not too much) since i have had it for so long and both my kids drove it as first car)

 

UPDATE: ISSUE RESOLVED
Tried switching wires on 1 and 2 and the misfire code cylinder moved with the wire. Inspected wire housing boot where it connects to plug and saw a tiny little burnt/melt line. wrapped it in electrical tape and misfire is gone. Ordering a new set of wires. jeez, the wires are only 3 years old and I just did not suspect them when i first started troubleshooting this.oh well.

 

Ah, Ol Occam’s Razor, thanks for updating the solution! It’d he helpful if you edit the title of the thread to include “Solved” for the future

 

Good find. Were they OEM wires?

 

@Daddykool , no I used the Walker brand wires from RockAuto. Will replace w/ OEM though

 

You can use NGK (blue) wires as well, usually its either OEM or NGK when you do wires