sometimes venture huge hickups

[OOge]

I have a chevy venture '00 with 70k miles. Everything worked perfect until yesterday. I took the exit at the highway and cruised in a little town. When I tried to pass a car and gave more gas, the car started to buck. I saw the RPM gauge going like crazy, from 1500 to 3500. A kickdown on the pedal solved the problem for a few sec. It shifted back to its lower gear and after that I could cruise in the 5th gear. But when I decreased speed, and wanted to give a bit more gas, it started again. Seems that it is begining to buck while it tries to shift from 1-2 2-3 and so on. no check engine light, only the battery icon lit up and went out. finally I stopped and put the car in neutral. I pulled the throttle cable and let the car reach about 4000rpm. Nothing, engine runs smooth. No hickups, no rough idling nothing. I refitted the MAF sensor cable just in case. Now check engine light lit up. the car stalled, and I started it again. Runs great. See a little fluctuation in the RPM. Normally it idles at about 600-700rpm. Now it runs between 700 and 1000rpm.

Drove to a shop and read the codes.
Replaced the possible issues.

- MAF sensor
- Oxygen sensor (upstream)


This morning I drove 25 miles no problems at all. Only one little hickup. Left the car alone on the parking lot, and when driving home problem came up. Stopt the car and pulled of the o2 sensor connector. started the car and problem still excists. It seems that when I kick down the gas pedal, it hasitates again, but doesn't show a hickup above the 4000rpm.
You can see on the movie that the rpm is fluctuating. It looks like the car is going to stall, but the computer keeps it running. Any idea. Could it be a fuel problem, EGR problem, as the scantool doesn't show any other problems.


made a small movie so you can see the rpm gauge fluctuating heavily
http://www.youtube.com/watch?v=RzHng60GZew

[lesterl]

So, you replaced an expensive MAF sensor due to a code stored because you unplugged it and set the code?

Have you done a tune up lately? Plugs/ wires? Have you changed the fuel filter?

[OOge]

I still own another venture with a bad headgasket. So I switch the sensors.
No did not do any tune ups.

[dewaynep]

Is the engine rpm following the Tach rpm? I can't hear the engine changing speed in the video. Also, is that the battery light that comes on in the video? You may have a low voltage or bad battery/alternator that is causing the tranny to shift incorrectly. What's the battery voltage at rest and with the van running?

[OOge]

Originally Posted by dewaynep

Is the engine rpm following the Tach rpm? I can't hear the engine changing speed in the video. Also, is that the battery light that comes on in the video? You may have a low voltage or bad battery/alternator that is causing the tranny to shift incorrectly. What's the battery voltage at rest and with the van running?

You can hear the engine lose power. So that's why I think the battery light comes up, because it is trying to stall, but the computer keeps it running.

[lesterl]

Yes, the PCM will drop out the alternator to try to prevent a stall.

Good to hear you didnt buy a MAF. As a side note I set a MAF code the other day, put my scantool in live data mode, found if I wiggled the wires to the sensor it would drop out the readings. I used a pick to tighten up the connection and it runs good again.

Is the engine kinda weak in the top end ...... high rpm is just noise and no power or low power..... My 99 I had was that way at 90k and I put plugs into it and it was a beast after that, I do recall some stalling and hesitation before but not after.... BTW also replaced the plugs in the 97 with some NGK's at same time as sensor repair and oil change and I think that helped with some of my issues no more rough idle in gear....