Very strange lifter problem
 

Hi, I recently rebuilt a 1.8 liter, 8 valve engine (code PF) out of a '90 Golf GTI. After I got it back into the car it only ran on three cylinders. Ok, no biggie. I removed the head, and the cam and checked all the valves, they were fine. When I put the cam back in, I noticed that the valve I thought was stuck open, was stuck open...So, I took the cam back out, and the valve shut. It's an exhaust valve, so I switched the lifter with another exhaust lifter, and the problem changed valves. Then I switched the lifter with an intake lifter, to see if I mixed them up before. The problem changed to the intake valve. So I figured that the lifter got stuck expanded, so I got another from a junkyard, and it did the same thing. So then I went to the dealer and ordered one, which also did the same thing. The dealer said that there is only one lifter for all those engines. So my question is, what the hell? It has to be the lifter, but where can I get a lifter that will work? Is there a such thing as an aftermarket head with different lifters?