Sounds like you have at least one bad glow plug. Disconnect the cable at the glow plug relay and check ohms between ground and each pin (individual glow plug circuit). The glow plug that has a skewed reading will be the one that needs to be replaced. Remove intake and swap out gp to fix. Remove gp with engine hot and after you have sprayed it with Kroil or something similar. Take your time removing it. I've had some come out in a matter of minutes and others take an hour to back out.

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Jim