This is actualy on an E150. Should be ame thing I'm assuming. My brother brought the van in hesitation on tak off, letting off the gas, it would idle rough. It has overr 120,000 on it. His shop put in new plugs, wires and injectors. Why injectors, I don't know. It's still runs rough. He brought it over last night. It had vacuum hose (looking from the rear) on the right intake manifold that tees to the PCV and somewhere else.. He said it was fill of rubber dust. It collapsed when the engine was ran. I replacedd it with extra hose i had. I just used Hi Pressure gas hose, that's all I had. It seemd to cure it. Then it started acting up again. At just offf idel, it acts ike a vacuum leak, and stays that way until about 1/4 throttle or better. We stopped at a local parts shop and borrowed their scanner (I'm a long time customer). It had P 303. Which means cylinder #3 misfire. Which could be anything causing it... any idea on where to look? Could Ford pile any more junk into that engine compartment?

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My 1997 F-150 4.2L had a p303, so I replaced that plug but still light came back on, end up being intake manifold gasket was leaking coolent into cylinder 3.

Are you losing coolent?