Need some input on low vacuum and idling issues

[EM.TT]

Just finished a rebuild and I'm having trouble getting it to run right. Here's the scoop.

-I have a steady reading of about 10-11 in of vacuum at idle which I know is quite low (should be 17-18 right?)
-It stays at 1k rpm for a while, then starts hunting, and will eventually die if I don't give it gas.
-It revs up fine, no backfiring, some occasional hesitation, but behaves normally for the most part. When I let off the throttle the vacuum snaps to about 20 in. so that says the rings are sealing (correct me if I'm wrong)
-I drove it around the neighborhood once and every time I went to give it more throttle than the amount required to maintain speed, it would sputter and cut out, no backfires though.
-Exhaust is clean, no abnormal coloration or odor
-No check engine lights. (found out there is no LED on my Ash ECU either so I can't test for codes)

Here's what I know and have done
-Boost leak test: no leaks, held pressure for quite a while.
-Timing is set at 15 degrees and belt is aligned correctly.
-TPS is set to spec.
-All injectors and coils are working.
-New PTU and harness.
-Correct plugs and are gapped correctly.

Based on my research it's running quite lean, but I don't know why. It has about a quarter tank of 91 w/o ethanol that has been in there since the beginning of summer. My brother added (on accident) a whole bottle of Isoheet in hopes to remove some moisture, and Im starting to think that might be the culprit, but honestly, I'm running out of ideas. I also just switched to a dual pop set up and have a Z1 eprom I purchased from a member on here, any odds a single pop tune would cause this? Any input would be helpful, thanks in advance guys.

[Ziggy1621]

Moved to the Technical Forum.

A couple things to consider:

1. Is the AC on? If yes, check the AAC
2. Have you tested the IACV by pulling the yellow plug off and see if the car catches itself. I had a bad IACV once that did something similar.

After this, I would get my hands on a consult cable and run something like ECUtalk to check voltages, etc

[t.mcginley.jr]

Without knowing codes it could be anything... O2 sensors, coolant temp sensor, fuel temp sensor, etc. You could check the voltages on these sensors via the FSM to get an idea if they're working correctly or not. You said it stays at 1k for a while and then starts hunting, is this after it gets warm?

[EM.TT]

Ziggy- I don't have AC, deleted it. I don't think I had it turned on whether that still makes a difference or not. I have not tested the IACV, I was wondering about that but wasn't sure how to test it. Ill give that a try this weekend. If that's the case, just replace the whole unit?

t.mcginley.jr- wouldn't the ecu turn the check engine light on if the O2 sensors were bad? Either way, I think i'm going to replace those just to eliminate variables. I was going to check voltages but ran out of time, and didn't really know which ones were necessary to check.

And yes, it usually does it when it's warm. On a cold start it would idle decent for about 15-30 seconds, then start dropping and hunting. Start it again maybe a minute later, it would go right into hunting and stumbling. It also struggled to regain a normal idle after I revved it up a little, more so when warm.

What are the odds it's a clogged fuel filter, or something to do with fuel delivery or pressure? FPR?

[itsa300zx]

You should still be able to check ecu codes, just look at the "check engine light" on the dash for the flashes.
If the eprom was programmed for single intake and you have dual, that will cause problems too.

[EM.TT]

Ok, only problem is there weren't any warning lights lit up, but I'll give that a shot if I'm wrong. I won't be able to do any testing and swapping until tomorrow night. I have a spare coolant temp sensor and IACV at home, hopefully I can find the damn things. I'll be swapping the oem intake piping back in to see if the tune is for a single MAF also. Thanks for the guidance gentlemen, I'll let you know what it was or what I figure out.

[EM.TT]

Well, I'm still confused... Turns out there is an LED on my ecu and was throwing a code 12 (maf harness or sensor). The harness is good, tested everything according to the FSM, and checked with another complete engine harness I have just to validate the results.

So, I picked up an MAF from a parts store (happened to be an N62) and that didn't help anything. It runs great until I plug in the MAF.
(If I start it w/o the maf connected, hold the throttle open a bit while plugging one in, I can get it to rev up past 2400 as it should, but It literally will not idle. Bounces and hunts from like 400-1000 rpm, then shortly dies and won't restart.)

Another concern I had was the tune but Im fairly confident it's for a dual MAF, it ran really rich and when I put the original T back in, and didn't run noticeably better.

My question is now, with the bigger turbos and no 'Idle balance kit' (like Z1 sells), would that be enough to cause these issues? Starting to feel like a real noob here...

[t.mcginley.jr]

Are you sure the MAF connector doesn't have any corrosion on it? The metal connectors would look greenish. This is a very common problem on our cars, almost any of the connectors can get corrosion buildup. Another possibility is that the female connectors on the harness aren't holding the MAF pins tight enough to make a good connection. A few people had that issue with their CAS connectors.

Are you sure the parts store MAF is a real N62?

And was everything running fine before you switched to the dual setup?

[Ziggy1621]

I'd suggest getting a consult cable on it

[EM.TT]

Are you sure the MAF connector doesn't have any corrosion on it? The metal connectors would look greenish. This is a very common problem on our cars, almost any of the connectors can get corrosion buildup. Another possibility is that the female connectors on the harness aren't holding the MAF pins tight enough to make a good connection. A few people had that issue with their CAS connectors.

Are you sure the parts store MAF is a real N62?

And was everything running fine before you switched to the dual setup?

They are clean, the whole wiring harness is almost new, along with the connectors. The maf was good, I exchanged a brand new budget one (working dummy?) as a core and it ran no different with the refurbished vs. original vs. cheap. I cleaned the entire CAS unit before I reinstalled it during the build, and I made sure that It was connected properly after I adjusted timing.

Everything was running great before. But I also just rebuilt the engine, added 2560's, and switched to a dual MAF setup with the filters under the headlights (with oem recirc's). I didn't install a 'low speed drive-ability' kit like z1 sells, and I'm thinking it makes a bigger difference than I thought, but I'm still not sure.

Either way, I think I'll be getting a Selin translator for my birthday but I won't know until next weekend at the earliest. Not completely sure if it'll fix it, but I want one anyways and it would at least eliminate another variable.

[hoonigan4l]

I went through a very similar problem.. Swapped my TPS and it ran perfectly. Although I did have to adjust the Tps afterwards to lower the idle, which I read and know now that I should've adjusted the idle Via the Iacv adjuster

[EM.TT]

I have two TPS's and both test the same, which I actually forgot about now that you mention it. I can get them both set to spec for idle, but then they only read 7.3 v or mv at WOT, which should be at 9 IIRC. Not sure if it being off on the high end means theres issues throughout the whole range, but I'll probably order a new one unless that's not an issue?

[t.mcginley.jr]

At WOT your TPS should read 4-5v, not 7 or 9 lol sounds like they might be bad. What is the reading with the throttle fully closed? Should be around 0.4-0.5v