Car Bucking in 1st and 2nd gears!

[240dreamer]

I have a 95 240sx manual and in 1st and 2nd gear if i give it much gas at all it begins to buck back and forth. It has been suggested to me that maybe a vaccuum line leak may be the culprit, or ignition, or fuel delivery. This is what i know...the ECU says it's the mass air flow sensor but i took that out and compared it to a working one and it seems to be in great condition. I just replaced the fuel pump and fuel filter; pump is now the high flow walbro and filter is 300zx TT filter. No injectors are leaking...i took the intake tract off today to see if i could find any leaks or holes anywhere and i couldn't. all vaccuum hose connections that i could find have been tightened or replaced with a better one. The car goes into a mechanic monday so i'm hoping that will help.

What's wrong with my car???

[TurDz]

Hmm, I always thought it was normal. On my 96 Maxima 5-spd, it did it a lot in first gear, mostly after cold starts or when the car wasn't warmed up.

For my 98, it doesn't do it at all...maybe on a few occasions. It was more of an annoyance factor to me but if there's a way to fix it or prevent it, I'd like to know how too.

[240dreamer]

that's interesting, i figured i was alone in my problem... stupid me. the bucking is really violent and doesn't require much gas to set it off onto it's tangent. Also, my 240 seems to do it worse when it's warm.

[NISTECH]

if the airflow is bad you will not be able to tell visually if you have a good one available to you put it in and try it to see if your car still does it.

[240dreamer]

ok, i got it into the shop today and they figured it out...try to bear with me... The ECU's signal that's sent to the Mass Air Flow Sensor isn't getting there sometimes. So the modified 12 volt signal isn't getting sent back to the ECU so for some reason the computer thinks it's hitting the rev limiter causing a momentary cut of fuel and ignition. Then suddenly the signal reaches the MAF and all is well for another 1/2 second then the cycle repeats. They have to track the problem down to somewhere in the communication lines between the computer and the MAF, it may even be the ECU itself, they mentioned. They're keeping it overnight so we'll know in the morning...

Also i found out that there's a leak in the Intake manifold to Head gasket in the #4 cylinder. That won't be all that difficult to fix but still, it's another problem i have to deal with.

So that's the problem, so they say, and there goes $200 in shop fees just to find out what it is... Oh well, whatever's best for my baby