Idle issue, I need you experts to help!

Basic tech questions such as future setups, different turbo kits, car diagnosis, etc
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kutworksinc
NooB
Posts: 6
Joined: Wed Apr 13, 2016 6:36 am

Idle issue, I need you experts to help!

Post by kutworksinc »

OK, here we go.

The truck is a 95 HB, 140k miles, ODB1, KA24E.
Truck has the following done to it. Its turbocharged (obviously). Its a show truck, not a drift/race vehicle. So the turbo is basically a cosmetic part / conversation piece. Its a small t3/t4 hybrid. Wastegate mounted on exhaust manifold. It has a 10:1 FMU. Stock injectors. Its set to 6 pounds of boost.

The problem is, it has a miss at idle. Sounds like its skipping a beat. Also, idle wants to drop until it eventually it chokes and dies. If you rev it, it will idle ok for a couple seconds, then start to drop and fluctuate again. If you stab the throttle, it will bog/stall for a second or two, then go. If you're driving, It runs great. Now, if you hold the throttle open just a hair, just to make it rev to 1500 or 2000, it still has a miss, but wont stall. It DOES idle ok for maybe 10-15 seconds after you start it.

So here's what I did so far. First, looked for codes. No CEL, no codes on ECU under the pass seat. Got a code 55, means "no malfunction". Ok, while Im working on the ECU, did a TPS check. Came back fine on the ECU. Ok, got it started, looking around the engine bay, I did a visual inspection. Nothing jumped out at me. I know it cant be an EGR malfunction, because there is NO egr. All EGR stuff was removed during turbo install. I got a can of carb spray, and sprayed it all over the engine bay, and didnt notice a change in RPM. Im not saying there was no change, but with the funky idle, I didn't hear anything. Next, I pulled the connector on the MAF, immeadiatly started purring like a kitten. Idle was flawless. Said ok, well, I have some extra MAF sensors, So I swapped it out. Twice. Same exact result on all 3. So Maf seems to be working. I did some searching on some forums, and another common problem is the Coolant temp sensor. Checked it out, seemed a HAIR off on the ohm readings, so i went and bought a new one, installed it, and no change. I pulled the MAF connector, TPS connector, and IAC/AAC connector, and checked base timing. Reset it to 15 degrees. It was about 16-17 degrees. So it on the 3rd mark to the right of the white mark. If I unplug the IAC/AAC connector, Idle gets even worse. I did pull the IAC and cleaned it. It wasnt stuck or anything, but it was a little dirty, and if i hook it to 12v it moved.

So where do I go from here? Am I chasing a very elusive vacuum leak? I didn't think pulling the maf and putting it in open loop would hide a vacuum leak, but I don't know. I dont HEAR a vacuum leak that big. I don't understand how it can idle so perfectly in open loop, and die in closed loop. Seems to me that its mechanically working, the problem is some wire or sensor somewhere. Which sensors are ignored in Open loop?

So far, its got

New MAF
New CTS
New Plugs
New Fuel pump

Any ideas guys?
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p00t
Encyclopedia-Nissan
Posts: 1170
Joined: Sun Aug 28, 2005 10:27 pm
Location: Detroit

Re: Idle issue, I need you experts to help!

Post by p00t »

Pull the injectors one at a time to find out what cylinder is causing it. Check compression on that cylinder, check the injector or replace, check/clean the cap/rotor, swap plug wires or use a spare.

Any time you can feel one big miss assume it is not a sensor because sensors feedback into ALL cylinders. <-important
Current Experiment: Project Twin-Charge 2022
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