Need some help!

[3HunnedZ]

Hello, I have been lurking NICOclub for a while now - usually whenever I google a problem I'm having on my Z32, NICO has what I need.
I need some help:

Started a few weeks ago:
When starting my '96 300zx NA M/T in the morning, it would start - rev to about 1,200 RPM, stay there for about ten seconds, then drop to 800.
After about 10 seconds idling at 800, it would drop to 500, bounce from 500-600 for a few seconds, then rise back up to 800. It then drops back to 500, repeating the process.
It did the same when it was warm as well. Once driving - there is no hesitation. Only when idling is there problems.

The Check Engine Light was on, so I ran it for codes, and got:
P0605
P0325
I cleared the codes.

After a bunch of searching - I came back with a list of things to do:
Check MAF, check harness connectors for green corrosion, check TPS, check IACV, adjust idle, change sparkplugs..

I changed sparkplugs from the Iridium plugs that the previous owner had, to NGK PFR6B11's.
Cleaned MAF sensor with MAF Sensor cleaner.
Checked TPS, CAS, PTU, Coolant/Water connectors for corrosion. (only checked, they looked alright so I didnt do any cleaning)
Cleaned Throttle Bodies
Put some injector cleaner in
Vacuumed the Stillen intake filter
Adjusted IACV, and half-*** cleaned it

No luck.

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Currently:
No Check Engine Light popped back up.
When starting it, it does the same - rev to 1,200RPM for 10 seconds, drops to 750/800 - then within 5 seconds, drops to 500 and then back up to 800
But, something different started:
In first gear, it would buck right after I took off. I put it into neutral, coasted for a few seconds, then put it back into first - no more bucking.
I thought I noticed that my 2nd gear was being 'dragged out' - WOT, the revs accelerate, just slower than usual (hesitating?). Then, after getting onto the freeway, and getting up to speed (70mph), I put it into 5th WOT. My RPMs start to drop, as well as my speed. What?!
WOT in 5th @ 70MPH, I lose speed. Downshift to 4th gear:
WOT in 4th @ 60MPH, I'm not losing speed, but I'm not accelerating either. Downshift to 3rd gear:
WOT in 3rd @ 45 -50MPH, it finally kicks in, and I have my power back. I upshift to 4th, and get back up to speed at 70MPH. Upshifting to 5th = lose RPMs again. 4th gear = stay at current speed at WOT.

Dropped the Z off to a Toyota mechanic I know who scanned the Z for codes:
P0605 is back.
And the mechanic was confused why Fuel System 1/2 went from Open Loop-Fault to Closed Loop.
Also, why the Air Flow Rate from MAF Sensor was only 5.07 g/s at 2,350 RPM --- 2.71 g/s at 637 RPM
(see pic)
http://i.imgur.com/t53Z7nb.jpg
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Other things maybe worth mentioning:
My radiator fan is ALWAYS on. Even when the ignition is at ON, but not started - its on. When I start the car, it stays on. Its always been like this?
5th gear grinds if I shift from 4th without letting it coast in neutral for a few seconds.
My car gurgles when letting off gas at high RPM

I will try to get a video posted of a cold start, warm start, and driving as soon as possible.

Any help is appreciated on what I could check next, suggestions, etc.

300zx-idle-problems-t340045.html
Has pretty identical issues as me, besides hes TT and A/T

Theres a post there that suggests that the Knocksensor might be the culprit. I did get a Knocksensor code a while back, but its never popped back up. What do you experts think about that?

[3HunnedZ]

Tested the MAFs sensors voltage - its reading .4 - .5 Spec should be .8 - 1.5
(as per http://twinturbo.net/nissan/300zx/forum ... oblem.html)

Tested the resistance on the coolant temp sensor - couldn't get a solid reading. The ohms just went up / down like crazy (tested in boiling water).

I'm going to call nissan and order a new MAF sensor and coolant temp sensor in the morning - will update!

[3HunnedZ]

After hearing the steep price of the MAF - I want to be sure that its actually the MAF.
Any help? You guys are a smart bunch.

[Ace2cool]

Sorry, OBDII isn't our strong point

Surging idle does sound a lot like a coolant sensor type thing.

Now, are you testing the MAF with the engine running?

[3HunnedZ]

Sorry, OBDII isn't our strong point

Surging idle does sound a lot like a coolant sensor type thing.

Now, are you testing the MAF with the engine running?

I tested the MAF with the key at ON - not running.
I picked up a used MAF for 80 dollars today - going to order the Coolant Temp sensor tonight. I'll update.

[Ace2cool]

Yeah, the FSM spec is at idle, so .4 would probably be about right. (That's what another guy is getting as well in his troubleshooting.)

[3HunnedZ]

Yeah, the FSM spec is at idle, so .4 would probably be about right. (That's what another guy is getting as well in his troubleshooting.)

Well, I replaced the Mass Air Flow sensor - and it runs like it should.

[Ace2cool]

Good to hear. Thanks for posting your fix.