P0300 Random Misfire and IDLE Issues (99 SOHC)

[Dsmhunter]

I would replace your PVC valve. Sounds like its stuck open and causing oil to pass by

[Dbeltran24]

There is no PCV valve on on the rear vacuum line, only the front. The front goes to the intake manifold and the rear goes to the intake pipe. Unlike the DOHC, the SOHC only has two vacuum lines from the valve covers. Not sure how the front PCV valve would prevent the rear from sucking oil in to the intake when the two heads aren't connected. Seems to me like there should be a second PCV valve on the rear, but there's no where to screw it in.

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[RealMcCoy]

If you have a vacuum source hooked to the rear cover, that is a problem... It's supposed to be hooked to the air intake. The PCV draws the vapors from the front cover fresh air goes in the rear cover.

[Dbeltran24]

Maybe vacuum wasn't the right term, but there is a hose from my air intake to the rear cover. I said vacuum because the oil is being sucked from the rear cover into my air intake. I just assumed it was a vacuum since there is suction.

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[Dbeltran24]

After doing some research on the PCV valve I see that the SOHC and DOHC work in different directions. I did replace the PCV valve during the rebuild, I wonder if I got the wrong one. Just in case, I ordered another one, this time from the dealer to avoid any chance of a mix up. I'm picking it up tomorrow.

Yesterday I finally got around to changing my injectors and fuel pressure regulator. I also replaced all my lifters, which were the only components in my heads that I hadn't replaced. I figured I might as well since I already had the plenum off. One less thing to worry about later.

When I removed the plenum I did find that gasket for the EGR pipe from my exhaust was not sealing properly. The article posted earlier mentions that this could be the cause of the random misfire. Going to pick up another one this weekend.

I'm going to replace all my vacuum lines this weekend too. Crossing my fingers that these changes fix my issues.

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[Dbeltran24]

Turns out my PCV was bad. Tried shaking it and heard no movement inside. Not sure if this cured the oil in my intake yet, won't know until I run the car for a while.

On another note, I no longer have a misfire after putting everything back together. Not sure exactly which part was the cause, since I replaced the injectors, fuel pressure regulator, lifters, egr gasket, and PCV valve before starting the car again. Either way, the problem is gone and the car is idling smoothly.

Now all that's left is fixing the oil leak between my motor and trans. At least that's easier to trouble shoot. The only places it could leak from on that side are the rear main seal, oil galley plug, and/or oil pan.

[Dbeltran24]

Looks like the misfire isn't corrected as I thought. Car idled fine in the garage, but the moment I took it for a spin I got the random misfire code.

Earlier in the build I had forgotten to tighten the crankshaft bolt and the pulley backed out a small amount when I started the car. This bent the crank angle sensor blade slightly. At the time, I straightened it out and re-installed it. It looked pretty straight to me, but I fear this may be the cause. I ordered a new crank angle position sensor and blade yesterday. Should be here in a couple days. I didn't get to the vacuum lines over the weekend as I planned, so I will change those out while I wait for the other parts.

This misfire is driving me nuts!!!!!

[Dbeltran24]

Does anyone have a diagram of how the vacuum lines are run on a 99 SOHC? Just want to make sure everything is connected in the right spot.

[Dsmhunter]

Have you fixed the misfire yet?