1990 300ZX Jumpiness/Hesitation

[zamazz10]

I have a 1990 300ZX N/A that started acting up a few months ago. I've been trying to find the problem since then using the service manual, with little luck. Here are the symptoms: when cold, it is especially jumpy in 1st gear. Not just jumpy, but it seems to lose all power when the accelerator is pressed hard. If I take my foot of and press it again it will apply power before repeating the cycle. It isn't as pronounced when hot, but is still noticeable. Right after being started, it will do this in gears 1-3. When cruising 60mph+ it seems to do the same thing. The power will cut out and I have to pump the accelerator. Often it will not accelerate at all in 5th. Even when it isn't jerking all over the place, it doesn't have the power it did before. Also, I have observed some pressure in the gas tank, like the cap vent is broken, but relieving the pressure does nothing. When I hooked my computer to the cars computer, one O2 sensor osculated around the middle while the other stayed low and only moved when the engine was revved. I'm sure there are more problems I am forgetting.

Any help with this would been greatly appreciated. It makes me look like a terrible manual driver!

[robomatic12]

Check the readings on the TPS, see if they are linear and don't have any breaks in it. That can cause the ECU to have no idea where your throttle is causing a jerking motion. Check with a mutlimeter with resistance or volts between two of the terminals.

[NORCAL300ZX916]

are u running on all cylinders? sounds like u have a missing or dead cylinder IMO. Try a power balance test.