Engine Miss @ Idle
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New User
Joined: Aug 2000
Posts: 7
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From: Missouri
Engine Miss @ Idle
My 96 4.9L has a miss at idle. It is showing two codes 302 and 420 when I check. I changed the rotor, dist. cap, plugs and wires after it ran really rough in the rain and that seemed to straiten it out for a week. Now the code 302 has reappeared (420 never went away) and it is running a little rough at idle. What should I do next, I have rechecked the wire on cylinder 2 and it doesn't appear to be jumping spark like it was previously, any thoughts on what to do next?
Postmaster
Joined: May 2002
Posts: 3,241
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From: Broken Arrow, OK
Engine Miss @ Idle
Did you use Motorcraft tune up parts? If not that could be your culprit. If all the parts you just installed are good, look for a vacuum leak on the #2 intake runner by spraying some carb cleaner around the gaskets. Swap the #2 wire with #5 and see if the problem follows the wire, then do the same with the plug. Go out at night and look for sparks where they shouldn't be. Spraying the plugs, wires and cap with water will help out here.
If it is a MASS air engine check the meter for contamination. I would expect that to affect all cylinders, but if you have a week injector on #2 it could hurt it more than the others.
If it is a MASS air engine check the meter for contamination. I would expect that to affect all cylinders, but if you have a week injector on #2 it could hurt it more than the others.
Thread Starter
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New User
Joined: Aug 2000
Posts: 7
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From: Missouri
Engine Miss @ Idle
The tune-up parts aren't Motorcraft but I got Npa plug wires, Champion plugs but not sure about rotor or cap.
I switched the plug and wire with no results, tried spraying the runner and all hoses with carb cleaner and haven't got a response. How do I check the meter for contamination?
One thing I forgot to list about the truck is that it has 150,000 miles on it and is fuel injected, so I assume it has mass air?
I switched the plug and wire with no results, tried spraying the runner and all hoses with carb cleaner and haven't got a response. How do I check the meter for contamination?
One thing I forgot to list about the truck is that it has 150,000 miles on it and is fuel injected, so I assume it has mass air?
Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
Engine Miss @ Idle
You might try a set of Autolite 5125's. I've never had very good luck with Champions. To check the mass air meter just remove it from its housing and see if there are visible contaminants on the sensor elements. They should be silver, if they aren't they need cleaned. A Q-Tip and alcohol work well. On some vehicles the mass air meter is used to measure barometric pressure. We had a van in last week with a rough idle caused by a barometer reading of 24.3 that should have been more like 27 or 28. Resetting the mass air meter fixed it. On this van we reset it by accelerating at over 3/4 throttle several times for 5-10 seconds each time. Don't know if that is the procedure for the 4.9 or not.
