chevy venture missing, jumping (long)

I have a 1998 Chevy Venture minivan with 210,000 miles. For the past seven month, the van has had a miss or stumble that occurs occasionally. It seems to happen most while traveling on the interstate as I begin to go up
a grade. The miss happens only one time per hill, it is usually very strong and harsh. I can sometime cause it to miss if I begin to increase the speed as if I had encountered a hill. The gas mileage has not decreased, nor has the power of the motor decreased. No smoke at any time and the van does not burn oil. Other than this single miss every now and then, the van runs great.
Things I have replaced or checked:
Spark plugs. (AC/Delco plugs) Plug wires, twice. Last time with Delco wires. 7X crankshaft position sensor. Fuel filter. PCV valve. Checked the fuel pressure, it is in spec and seems to change pressure properly. Both oxygen sensors. Catalytic converter twice, last time with a GM converter. New battery. Rebuilt alternator.
No codes are stored, the service engine light does not come on. I have an interface and can connect the OBD II to my laptop, but this does not show any problem with the various sensors, and the OBD indicates a "pass" on all onboard tests. Any ideas or help is greatly appreciated, Terry
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Look at misfire counts as this happens on a full function scanner, try some Chevron Techron FI cleaner, look as s/t fuel trims if you can get this to happen.

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Shep wrote:

I watched the fuel system trims and they change as I drive, mostly staying in the negative, but they do occasionally go to +2.00 or so as I accelerate. I am not sure what they should be, however. I will try the Chevron Techron FI cleaner, but I did use some gas drier last winter, no change. Thanks, Terry
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If you have enhanced option on your OBDII scanner check it for misfire counts as Shep said. These wont set a code until they reach a threshold but may give an indication where the problem lies.

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Woody wrote:

Unfortunately, my scanner seems to not have this option. Thanks for the reply anyway. Terry
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If your Chevy Venture is missing, then I would call the athorities and report it as being stolen asap. The sooner they know the better chances of getting it back. You say it is also jumping....sounds like a low rider with the air shocks for jumping, but I don't know why you would invest that type of setup in a Chevy Venture.
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In thought it would be wise to say:

Have no idea what's happening with yours, although I am interested in hearing what others may have to say.
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Terry wrote:

Have you had the intake manifold gasket checked? These have a nearly 100% failure rate by your mileage.
John
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John Horner wrote:

Yes, it has been replaced. Terry
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replying to Terry, John wrote: I have the exact same problem w my 99 venture. Replaced plugs,wires,computer. Found loose coil where the bolt had backed out. Replaced the coil and it ran fine for 1 month then started it again. Any ideas would be appreciated. John C.
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