''97, VTEC, auto, 124k. Car was running good, no serious issues. I was passing slower traffic on a two lane, needed a little more speed to pass, stepped into the throttle a little harder, car downshifted into second and began missing, sputtering and slowing down. I thought it was going to die right there. It continued running but is running REALLY rough. The codes are O2 heater circuit (I knew about that), but the new ones are P303 and P304 (cylinders 3 and 4 misfiring), and a P1300 (Multiple Cylinder Misfire Detected). I reset the codes, still rough. Pulled out the plugs, grounded them and checked them on their respective ignition wires, they were both firing fine. Takes about a mile of driving before it will go over 30MPH. Need to lift throttle to allow it to shift into third and fourth. Have no clue what to look at next. Thank You

 

Check if the timing belt has slipped.

Your coil may be partly bad and firing weak, or there is a crack or burn in the distributor cap or rotor that is letting the sparks short out.

Also don't drive far when misfiring like that, as you will burn up the catalytic converter.

 

Thanks, I didn't think it was the timing belt, because I had just changed it a few weeks ago. I will check it though. I guess I'll break down and give it a tuneup. I didn't think it was that because of how suddenly it happened.

 

Found the problem, the timing belt had jumped a tooth. Why would a new timing belt with only a few hundred miles on jump a tooth? How much play is allowable? I have nearly an inch play on the rear side, but since it was a new belt I thought this may be acceptable.

 

Clearly, that is too slack. Go through the tensioning procedure again. The spring on the tension roller needs to be there to set the tension initially. Then you lock the tensioner down by tightening the bolt before running the engine.

I would be inclined to replace any belt that has skipped even if had no miles on it, as skipping and running loose is going to be hard on the teeth.