Pulsing at cruise speeds, dying while braking. What's going on?!
 

So I've been having this issue going on for a few months, and it's getting rather annoying to say the least.

I think my 2005 Roadster is possessed. While I'm at cruising speeds, the car will pulse randomly. Most of our city speed limits are 35-45, and my commute to work is 55-65. So it happens at lower speeds and higher, but the car will pulse/jerk and I can see the tach drop a couple hundred rpm.

It also feels like the throttle becomes unresponsive at times while this happens. I can let off the gas when it is pulsing, but when I try to get back to it, the tach doesn't move and the car doesn't accelerate. I'll have my foot on the gas for a couple seconds, or more, then it will finally kick back in and go.

Then, when I'm coming up to a stop, the car will stumble and eventually die but it turns back over just fine without any issue. But then could die at the next stop light. BUT... if I go up just a block or 2 and have to brake again, the car MIGHT not die. Almost seems like if I don't go over a certain speed or rpm, then the car doesn't want to die. BUT... if I come up to a stop, and hold down the gas at the same time, the car won't die.

I don't have anything crazy done with the car. Only a CAI and exhaust.

My brother helps me work on my car, I don't remember everything he has done but this is what I can think of off the top of my head.

Replaced cam sensors
Replaced crank sensors
Cleaned throttle body - didn't help so replaced throttle body
Replaced MAF and MAF wiring
Replaced plugs and wires
Replaced IAC Valve
Battery and Alternator test good

I think he had replaced a couple other things, but cannot think of what they are. Anybody have any other suggestions before I drop my car in the bottom of the ocean?

Hook it to a live scan tool and check your PIDs (particularly your TPS value.) What does it read when your foot is off the pedal and what does it read at WOT?

And I know I sound like a broken record here, but... MILEAGE?

curious about these lines here--- so what exactly should those readings be? recently- i got a bluetooth ODB2 scanner that I leave in all the time- and frankly- some of the things that it is monitoring- i am not sure what the values should be or where to find a correct listing for them-i've looked but the posts that i've waded through around the net all seem to wander off in crazy directions- and since you are the one to have asked for those numbers from the OP- i figure- you got answers :)

Everything's in the FSM.

Sorry for the delayed response, had an emergency I had to deal with and couldn't get back to here.

Mileage is 112,xxx

Forgive me for sounding like a noob, isn't the TPS part of the throttle body? If we changed out the entire throttle body I don't know how the TPS would matter? I'm not trying to sound like a jerk, I'm asking a serious question. I don't know a lot of the mechanic side of cars.

stop throwing parts at it, take it to nissan for diagnosis.

also, if you changed the throttle body... you need to do throttle position relearn, idle air relearn etc

I have had a nissan tech look at it, their recommendations were first the cam sensors then maf, which we did. After that, they had no other suggestions.

We have also done the relearns each time we replaced different parts.

Going to step out on a shakey limb here. Hook up an old school vacuum guage to intake manifold. Idle until warm. If it's not almost still, you have a vacuum leak. Step on the brakes and watch the guage.

I could be way off base but if it were mine, I'd have a magnifying glass on that Power Brake Booster hose.
gl !

Your problem description sounds as though the problem is one or more camshaft sensor(s) or crankshaft sensor(s).

Hopefully my advice can be confirmed with a digital reading from the Consult.

--Spike
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So after having Nissan look at my car a couple times, they still could not figure out what was going on. Everything I had them replace, they warrantied them out just in case I had some failures, and just to make sure all parts were working properly.

Scanners were not throwing any error codes after replacing all of the aforementioned parts.

Everything that everyone suggested has been completed, still no errors on scans.

But alas, I have figured out what the problem was! Or at least I hope so, since I haven't had any issues since Saturday. It was an issue with the CAI filter! I don't know what it was, but I swapped it out and it's been running like a champ ever since. Maybe something defective with it disturbing the air flow? I couldn't see anything physically wrong with it at a quick glance. Maybe there's a crack in it somewhere that I can't see, who knows. I'm just glad it's running good again.

Congrats. I was gonna' say water in the gas, but that would've been lazy of me.. Heh. I'm tired today. Glad it's running.

The OE Nissan airbox is great. No need to change to aftermarket on the Z unless you're going FI. Glad you got it back to normal.