loss of power while driving engine doesn't shut off and idles fine

2000 inifiniti G20 - Car idles fine, gears engage fine, clutch is not hard to depress, no slippage.

However, car has a complete loss of power, seemingly returning to idle even while driving.

I can floor it while in gear and get NO power...just idle it seems but when I down shift it will rev up.

A mechanic has looked at it for three week he claimed it was NOT the clutch or MAF Sensor. Replaced O2 sensor.

Dealership just charged me 125 to say it was the clutch and master cyl....

But this makes no sense to me.

Welcome to the forum!

You might have better luck posting this to the G20 forum. For starters though, has the shop you had look at it pulled spark plugs, checked for diagnostic codes (pending or current), or checked the fuel pressure? When's the last time the car had a tune up?

-Rod

Ditto with getting better results in the Infiniti forum. It sounds as if you have a manual transmission so that eliminates many potential problems with shift solenoids and problems within the valvebody. But to me it sounds like it could be either a speed sensor, throttle position sensor, faulty O2 sensors, or even possibly a engine temperature sensor.

Find a place to scan your codes for free (auto parts stores) and post back here if you don't get a better hit in the Infiniti forum.

First Check all basic items
Plugs, wires, fuel pressure, vacuum lines, pcv, air filter, etc. as they apply to your car.

then one thing is check you catalytic converter, a plugged cat can cause a no power off idle situation!

Check your catalytic converter .