shake and stumble during shifting

[qatcool]

I need your advise.

 

My pathy runs just fine at low rev between 1500 - 2000 rpm, as i step on the gas pedal, and it reaches 3000 - 3500 when it shifts it will shake, as i release the gas then the next gear will come, i have replace the fuel pump and filter nothing happened. when the whether is hot it does even at 2500 rpm. can somebody advide what look for the problem. can the MAF do this? distributor maybe?

 

is my transmission failing?

Edited June 27, 2013 by qatcool

[wofat]

Is it speed related or just rpms? Speed = tires/wheels/hubs.

Do you have engine codes?

If it's auto transmission I'd say emisions (vacuum), manual might be anything in the clutch/throwout bearing or a u-joint.

 

 

 

 

 

 

 

Maybe a vacuum leak somewhere, does not sound like the transmission. Do you have a check engine light on? Can you pull a code?

[Nefarious]

Could be the maf. I wouldn't be a new one just yet tho. Run the maf test in the fsm and see what it specs at first. Check all engine grounds. make sure no electrical plugs have corrosion or loose pins. Then after all that try again. If its still acting up then continue with the diagnosis. My 2 cents.

[ThaBigPerm]

Maybe not related, but it's worth throwing out there in case someone else encounters the problem. Many moons ago a customer came into the shop I worked at complaining that their car stumbled horribly when driving around. Step on the gas, stumble stumble - but ran absolutely fine when parked in P or N. Put the car in gear and try to rev the engine with the brakes on, stumble cough stumble as well. Back in P or N, ran fine. :0/

Electrical diagnostics turned up nothing. After deciding on pulling/cleaning the MAF sensor as a Hail Mary, the tech found a hidden (underneath, between the little accordian groves) but significant crack in the rubber MAF->throttle body air tube. What was happening is that the crack self-sealed (mostly) when the engine wasn't under load, hence it ran fine. When the engine torqued (driving or in gear with the brakes on) it opened up this crack, creating a massive vacuum leak downstream of the MAF sensor (effectively bypassing it - no bueno).

[qatcool]

i have a code for knock sensor, can this cause this? when the engine is cold, it runs fine and shifts fine,but it get hots thats when the stumbling happens. even in neutral, when its cold you can rev up to 6000 rpm, but when its hot it only rev up to 3000 rpm and its start to shake. my 1st suspect is the MAF but a mechanic told me that it might be the fuel pump. is their a replacement MAF can you please give me the part code that fits VG33E.

[Kingman]

The cracked intake tube is a very common problem on the Z31 300ZXs, most complain of it running like crap in 1st and 2nd gear where the enginemoves the mmost, but running fine out of gear. I was going to suggest checking but doesn't seem like the problem now.

 

You said you already replaced the fuel pump so it shouldn't be that. And, yes a bad knock sensor can cause those issues or it is picking up knock as a symptom.