Engine Performance problem
2002 Chevy Venture 6 cyl Front Wheel Drive Automatic 89000 miles
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spits and sputters while you press on the gas . idles fine. when sitting parked, if you press the throttle, it runs choppy. only does this for a little while when driving after the van has been sitting overnight. once running a while, it runs good. All O2 sensors and catlytic convertor have been changed. Is this fuel pump Problem?

Could be fuel pressure, throttle position/MAF/MAP sensors and the EGR valve opening too soon-problem

Not to "thread jack" But, I too am faced with the same problem. My friends van is doing the exact same thing. 2003 Chevy Venture 4.3 V6 roughly 163,000 miles. But, everytime hers hesitated it would log a DTC of P0420 (Cataylist Effiency Below Threshold Bank 1)

She could let it warm up for about 20min and it would drive fine all day.

So, I changed the Cat Conv and the O2 sensor behind the cat. It was fine for about 3 weeks, then hesitated again and logged the same DTC P0420, but went away. I did notice that she has a small exhaust leak and it is getting worse. Could this also cause the P0420 code???

We then it alsmost died on her, the battery light came on for a second and then went out. She revved the van and then drove home. Tested the battery and found it to be bad installed a new battery and will wait and see if she has anymore problems.

I did notice that she has a small exhaust leak and it is getting worse

False" air can enter the exhaust through leaks and upset the O2 sensor readings

Would the exhaust leak cause it to hesitate???

She drove the van this morning and it gave her troubles for about the first 20min of driving. (But, also during the hesitation period it never logged a code and the light MIL never came on). After that it drove perfectly fine all day with no hesistation.

I dont think it is the fuel pump due to the fact that if she lets the van warm up for about 15mins then dirves it, the van works flawlessly. So, I am still a little frustrated and any help is greatly appreiated.

rasmataz wrote:

Could be fuel pressure, throttle position/MAF/MAP sensors and the EGR valve opening too soon-problem

Wouldn't all of these set a DTC??? I have worked on one vehicle (99 Dodge Stratus) that had an issue with the EGR valve, but it was with "Insufficent Flow" P0401. But, now on this Chevy Venture I get no codes???

Would the exhaust leak cause it to hesitate??? The extra air will cause the oxygen sensor to read lean condition and send this to the computer.

Ok, the exhaust leak is right after the first O2 sensor in the flex joint I will have this repaired and reset the computer and try that out. What about the egr valve would I be able to test it with a vacuum gauge and at what vacuum should it open fully????

rasmataz wrote:

Would the exhaust leak cause it to hesitate??? The extra air will cause the oxygen sensor to read lean condition and send this to the computer.

So, in essence it would cause the van to run richer than normal right??? If it was sensing it was too lean it would logg a DTC correct??? Well if so then it is not doing it. As for the MAP/MAF sensors what are there values (vacuum/air flow) at idle??? Thank you for all the info.

The EGR valve apply vacuum to it-it should stall or idle erratically. MAP voltage

Idle 1.0-1.5volts

WOT 4.0-4.9 volts