Nismo_sam

Alright guys, so I just had my heads rebuilt by a reputable shop(HKS cams, BC springs/retainers) Hot tanks,decked and all. Along with that a new Garrett turbo, new injectors and a 300zx maf. I have a very good Nistune tuner in my area and he gave me a solid basemp for my car(He just tuned someone with a stepup almost identical to mine as well) Well the car now runs bad after being built, not even drive-able. Shop said they have done all they can do to make it run any better, and that they have checked everything. Injectors, maf, coils, timing, etc. and that the car won't run better until the tuner can tun out the problems. Had the car brought all the way to my tuner's place and after near 5 hours of work he said that it pretty much can't be a tuning issue. In those 5 hours obviously we did a ton of trouble shooting, with no real results.

Now for how the car runs, it will start and idle around 1500rpms but is constantly like bucking up to anywhere between 2000-2500 rpms, literally like someone is constantly pressing on the gas and letting off. If you try to drive the car, it nearly cuts off upon throttle and would accelerate when you let off, very jumpy.

Also ps. We did a compression test and it was fine. The car throws no codes except for 55, which is all good.

Anyone that has any advice please chime in on this!
if you need more info on the car, just ask. Sorry I can't put up a video yet, been running around for the car since 7am and just got home around 11:30pm

KiLLeR2001

Did you check the TPS sensor resistance and voltage to see if they are within operating spec?

edit: Also, check the idle air control valve?

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Nismo_sam

Checked both at the tuner's place, both were fine

KiLLeR2001

I'd probably replace the CAS with a known working one. If the problems still arise, I'd start thinking about using another ECU with the nistune.

Given that all your other tests were done thoroughly and everything checked out as you say.

edit: Hows the MAF wiring? Do you have the protective shielded wire that surrounds the signal wire installed, could potentially be causing interference not having this. It's also to my understanding that the shielded wire is grounded at the ECU end only.

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s14jesse

Plug in a stock ecu and maf if possible to instantly eliminate the tuning issue could be an electrical issue as well like possibly a brake in a wire/s
I'm pretty sure it's not a mechanical issue have u checked idle air control valve ?

Nismo_sam

We did use another ECU from his 240/nistune, same issue. However we did not check the CAS as the shop said they did several times and that timing was spot on. I'll try to source a new CAS to see if it's the issue though, as my tuner should be able to just let me use his from his 240.

Nismo_sam

@ S14jesse Thanks, maybe I can try that tomorrow. Oh and I have checked the idle air control valve.

s14jesse

Put it all back to stock and if still doing it start to wiggle the harness I've had a few cars that I worked on and I did that that to detriment bad harness and boom fixed lol. Good luck Brotha hope ur car runs good soon

Nismo_sam

@ Killer2001
I'm not sure if I do or not, can't remember at this point of my brain being fried from this, I'll check first thing in the morning though.

Darren

how's your coolant level? did the coolant system get fully bled? air pockets in the cooling system can cause your strange up and down idle issue

Nismo_sam

Coolant was replaced/bled at shop, but will check on the level tomorrow morning.

Nismo_sam

Hey guys, here is a video I found of almost exactly what my car is doing

SR20DET Redtop surging idle. - YouTube

The only difference is I am idling higher

waste_of_space

My car did that, and it was a bad MAF. Didn't throw any codes, because my ECU was still getting/seeing MAF voltage, it was just incorrect voltage. Unplug your MAF, and see if your car idles better. There's a chance you've picked up a bad z32 MAF.

Also double check for vacuum leaks. I had some slightly loose bolts on my intake manifold. Make sure you check for and elimate all vacuum leaks, MAFS are very finnicky.

Nismo_sam

See we thought it was a bad MAF at first, so the first thing we tried is called a buddy with one in his car that was working and we pulled it out and put it in mine, same issue.

KiLLeR2001

I don't think the issue is the MAF, but the MAF wiring itself. The signal wire needs to be shielded otherwise the signal could receive interference, especially since with SR swaps the wires need to be extended. It really sounds like it has something to do with the wiring for the MAF, I'd follow it all the way back to the ECU to be extra sure.

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ShadowMan

dont forget to make sure your fuel pressure regulator didnt shit the bed either.

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in any situation....thou shalt blaze

Nismo_sam

Got the problem fixed a while ago, turned out to be a vac leak on the intake manifold. Up and running good now!