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The belt has nothing to do with the actual problem, but if it started since it was replaced, my first suspect is an engine vacuum leak. When the belt was replaced, something may have been left loose, disconnected, or damaged. As far as plugs and injectors, it would really have to be a coincidence. Nothing done would directly affect them.
Here is a link that explains how to check for a vacuum leak. See if it helps. Also, make sure nothing was disconnected with the air intake tube from the air filter box.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
Let me know what you find.
Take care,
Joe
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Thursday, July 4th, 2019 AT 7:54 PM