Rb25 Gurus Needed

[singlecamslam]

This is kinda a long read, so bear with me. The motor at hand, 1997 rb25 s2, in a 240sx, I'm in the USA.

The problem is about the common stalling issue while blipping the throttle or coming to a stop, it would always stall. I have narrowed the problem to the IACV, and heres why i think this is so:

On dead cold starts, the car starts and idles at 2k like its supposed to, so i figure the air regulator is working properly. When the car hits 50+ degrees C, the idles drops and stumbles instantly like switch has been pressed. THis is when the car starts to stall when i blip the throttle, by the time it reaches 85+ deg. C, it stall much easier and constantly when i throw it into neutral.

I checked power going to the IACV plug, has power. I checked continuity between ECU pin 4 (as per FSM instructions) and plug, has continuity. But, when i apply a ground directly to the plug, the IACV works, i can hear air circulating and the car stops stalling. WTF? So for some reason i'm not getting a ground. And when i apply ground i cant change the idle no matter how much i adjust the screw, but it does idle, around 800-900, and most importantly doesnt stall, no matter how much i blip the throttle.

Can i just wire in a ground directly to get around this problem? Ideas? What could be going on here. Thanks for any help.

[89CAL]

With ignition key on, their should be voltage between AAC valve terminal 2 and earth

Also should be continuity between ECCS C/U (ECU) Pin 4 and AAC terminal 1

The other test it shows must be using some sort of diag tool or laptop (possibly Consult) because you can raise or lower the AAC valve opening degree to test it.

Have you tried cleaning the AAC valve? Reset the ECU (If it is standard)? What mods does it have (does it have a vent to atmosphere blow off valve)? Is the problem new (Since you have fitted something) or been happening for a while?

Also found that resistance accross the coil (AAC Valve) should be about 9-10 ohms)

Edited December 11, 2013 by 89CAL

[533 RYC]

2,000rpm is fairly high. It should go to about 1,200rpm on start, then drop to 900-1,000rpm within 30 seconds.

When you say 'dead cold start' what's the ambient air temp?

You could possibly have a vacuum leak. As the AAC compensation decreases, the ECU recognizes too much air vs AFM flow & hence the stall when you blip the throttle.

[singlecamslam]

With ignition key on, their should be voltage between AAC valve terminal 2 and earth

Also should be continuity between ECCS C/U (ECU) Pin 4 and AAC terminal 1

The other test it shows must be using some sort of diag tool or laptop (possibly Consult) because you can raise or lower the AAC valve opening degree to test it.

Have you tried cleaning the AAC valve? Reset the ECU (If it is standard)? What mods does it have (does it have a vent to atmosphere blow off valve)? Is the problem new (Since you have fitted something) or been happening for a while?

Also found that resistance accross the coil (AAC Valve) should be about 9-10 ohms)

I have power and continuity, i followed the FSM instructions. I have always had this problem, The BOV is atmospheric, but it doenst leak, tried unplugging it, spraying starting fluid directly at it, etc. I have 3 AAC's, i found here in the states the sentra has the same aac so i swapped it out. But like i said, as soon as i apply ground to terminal 1, the AAC works and no more stalling. I did a half assed vaccum leak test with some starting fluid i will do it again, i did clean it as well.

Ambient temperature when starting is slightly above freezing, its around 2k, my rpm gauge is 100% accurate as its in a 240sx, Would it be a bad idea to make a separate ground for the AAC so this thing would stop stalling? I'll do another vaccum leak test and go nuts with the starting fluid.

Mods are: greddy style intake plenum, 3 in exhaust, thats pretty much it, stock ecu, rb20 wastegate. I think i'll make a video when i have some time, kinda hard to explain exactly whats going on.

Edited December 11, 2013 by singlecamslam

[89CAL]

Put a stock BOV on (if you have access to one) or a plumback BOV and then reset the stock ECU

90% of the time this is the problem. It has nothing to do with the valve sealing, its got to do with the way it can operate when you come off throttle. It can let some of the metered air out, the ECU will throw to much fuel in (Because some of the metered air is gone) and this can stall the car or get it close to

Even if you dont think its the issue, try it anyway.

By the sounds of what you are doing, the AAC valve solenoid will be opening fully and might just be enough to keep the car running. From what I understand, the AAC valve never gets to full open under normal conditions.

[singlecamslam]

Put a stock BOV on (if you have access to one) or a plumback BOV and then reset the stock ECU

90% of the time this is the problem. It has nothing to do with the valve sealing, its got to do with the way it can operate when you come off throttle. It can let some of the metered air out, the ECU will throw to much fuel in (Because some of the metered air is gone) and this can stall the car or get it close to

Even if you dont think its the issue, try it anyway.

By the sounds of what you are doing, the AAC valve solenoid will be opening fully and might just be enough to keep the car running. From what I understand, the AAC valve never gets to full open under normal conditions.

I"m going to plum the BOV back in, next on the list. I wired in the aac valve directly, meaning constantly open, car started stalling again. The hotter it gets, the worse it becomes. Idle is still kinda unstable, slithgly better. I adjusted the TPS, .5 fully closed, 4.29 fully open, cant get it any higher than that. No vacuum leaks, i went crazy wiht the starting fluid. Also, car does run rich, i know RB's arent very gas friendly, but i'm getting about 22 highway MPG, and if i'm boosting, forget about it. BOV will be next.

Heres my question, when i unhook the vacuum to the BOV, shouldnt that rule it out as a fault? Since its getting the same amount of air as if its recirculated, to my knowledge the BOV doesnt leak, i sprayed fluid at it directly, its an HKS. Appreciate your help BTW. Will try to plum it back when I find my coolant leak and someone to weld aluminum.