Bad MAF or TPS?
 

So i noticed a couple days ago that the throttle response in my car became a little delayed...when down shifting/rev matching, rev's round actually DROP when i tapped the throttle, then they would rev up a bit...it was weird...i also noticed while doing some running around that day, that every time i would start the car, it would rev to 2000 RPMS immediately on startup, and take a few seconds to settle down to 1100 or 1000, which is where it idles.

I parked the car that day, and it was supposed to rain...and i dont allow my car to see rain (i'm a baby, i know...)so it sat for a day and a half...i go to start it today, and it ran super rough for about 10 seconds, struggling to even keep up at idle...and after a few seconds it just died...

a little frustrated, i got in my beater and went to work....just got home now, popped the hood and checked for any possible vacuum leaks, or at least the hoses i could see without any serious work...all looked good...all coil packs in position good, PTU hooked up and not shaken lose or anything etc...

i try and start the car again, and same thing, rev's up to like 1500 RPMS, then becomes very rough and bobs at about 600 RPMS and appears as if it's going to die, but i shut it off on my own before it had a chance to. One thing i did notice this time around though is that the fuel pump was humming very loud the whole time, just sitting at idle, not even touching the gas...it was in it's higher/highest speed, which it should not be unless i'm accelerating...

So, i texted a local friend who knows his shit, and his best guesses are a bad/going MAF, or the Throttle Position Sensor may be bad/going/angry with me...

Opinions?

Is your ecu kicking back any codes?

check ecu for codes, 2nd.
easy check, pull the plugs for the MAF and TPS. Clean them and start the car again. See if that made a difference. Some dielectric grease might be in order.
have a multimeter? check the leads to the fuel pump. See if it's in spec. If you have cause to believe that it's malfunctioning, check it. do the same with the MAF and TPS.

Here's the latest... (situation hasn't improved at all...)


Checked for codes, got a 55...all good there.

Played around with the throttle bodies a bit, no sticking, no excess play, etc...


Checked the Throttle Position Sensor, no corrosion, cleaned it anyway, tried starting car without it hooked up, no difference...

Checked the MAF, again, no corrosion/signs of damage, cleaned it anyway, tried starting car without it hooked up, no difference...

Swapped over the MAF/Intake from a friend's perfecting running Z, no difference...


Now, i started the car...it bogged down and died, as i expected...but it's not starting back up! It's turning and turning and turning, but won't fire up...



I love this trend recently...something goes wrong, i go to fix something, and end up with a bigger problem...

I can understand if i did something wrong to cause a bigger problem...it was bogging down and then restarting fine (only to bog back down again) every time...until now, it bogged, died, and stayed dead...

I'm not a Z32 expert by any means, but generally a bad MAF will cause your Z to not rev above 2500 rpm. To me it sounds like either the fuel pump could be dying (check with fp gauge after replacing the fuel filter), a bad AIV valve, or EGR valve. If there are no vacuum leaks, take off the EGR and inspect it to make sure it isn't sticking open. Anyway, good luck and I hope you can get your Z fixed soon!

You
 

Might have a vacuum leak past the MAF check your hoses.

I know they say not to but if you pump the gas while cranking it does it finally start and run rough for a few seconds? If you rev it for a about 10 seconds to above 2krpm does it settle at a good idle? If so then you might have a bad (read corroded) connection to your battery at the terminals.

What happens is you build up a layer of greenish corrosion between the terminals and the cable clip. When you go to start the car you actually arc through this oxidization giving you enough power to turn the starter but little else, So you don't get enough gas/spark to actually start the car.

(joke reply: "sounds like you got a cracked distributor")

hehe, that sounds like the theory of the weakest part replace, new weakest part, replace, new weakest part, replace...vicious cycle.

i bought and replaced the fuel filter...but just for shits and giggles, before i put the new one on, i pulled the hose off the old one, and turned the key with the old filter pointing into a bottle...and sure enough, when the pump primed, fuel shot into the bottle...so the filter was fine after all, and so is the pump...

i went and put on the new filter anyway since the gas of returning it was just about the same as keeping it lol...but tomorrow i'm gonna see if any local friends have made a boost leak tester i can borrow...


but...no boost/vacuum leak would cause the car to completely not start at all...

and the batter terminals are fine...everything electrical in the car works fine...including the starter...it hasn't missed a beat with all the times i cleaned something, moved something, and tried to start the car today...

i'm gonna check for spark in the morning...but i doubt that's my problem...even if a coil or 2 is bad though...the car would still start...just not with all cylinders firing....

ugh i'm so confused...

My 300zx does the same thing, the only difference is I also need to replace a maf. Check your power transistor unit. If your PTU isn't bad check the two wire harnesses that lead up to it. Its located at the front on the passangers side, it's mounted directly on the engine block. It's kind of wedged in between that and the hose for the radiator.

If its fine check for any corrosion in the harnesses, also check for any loose seals on the harness that would possibly cause a bad connection. This is always the problem when mine refuses to start, idles rough, or accelerates poorly.

Usually when I can't get it to start I flutter the gas pedal and keep cranking it over. The longest its taken is 10 Minutes to start. I know its not the best thing for the car but if you need to start it, that's what mine take to get it done.

Hope it helped