Well it appears you are OK in the valve area. I doubt it is a fuel mix problem on a non-turbo. It maybe, but that would be a first in my experience. The next thing I would recommend is to check timing related issues. The 1G timing can be set with a light. It should be 5 degrees BTC when the timing connector is grounded (brown connector behing battery). There are two possibilities here: you are off time or the timing belt has jumped a tooth (and you are really freaking off time). If your belt is old or you went cheap on the last timing belt change (didn't replace tensioner), you really could have slipped a tooth.
I would check the timing first. It is somewhat easier. All you need is an alligator clip to ground the brown/tan connector behind the battery. Do this with a hot engine. If you ground the right connector (there is a pump tester back there too...I think) the check engine light should come on. Then connect a timing gun up to number one (drivers side plug wire). Fire it down on the drivers side and look for 5 degrees. If you read 15, you may not have grounded the wrong connect, but you are probably OK regardless. This whole proceedure is on
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last time I looked.
If timing is off you will need to loosen the cam angle sensor on the passenger side of the head (12mm nut) and rotate it to adjust. The sensor is a round bell that is probably green (copper). If it WAY off, you need to check the belt. This part requires more work as you will have to remove the timing belt cover (upper and lower) and all the accessory belts. Then you will need to line up both cam marks and the crank mark to make sure you are properly timed. If not, you will have to get dirty and do a timing belt. If not, you are driving a grenade.