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Hi Scott, It is a 2.6 rb26 with a fairly large turbo! The ECU is an apexi powerFC, I use datalogit to manage this (I tune it myself and turn off O2 feedback as I can get fairly decent values myself) There is temp correction but the temp reading stays around the same which is weird; I think it's reading hotter than it actually is though. The AFR gauge aligns with the value that is being read from the laptop The air temp sensor is reading the correct voltages within the standard parameters The injectors are 1000cc which made idle tuning a bit tricky but that's all fine and she boosts/drives just fine. It's only after a long drive that it starts getting lean, similar to starting the engine again after leaving it off for maybe 15 minutes although not so bad as this. I do suspect it's just a heat soak issue which is why my latest project is to replace the sensor with a more appropriate one and fudge the resistance with some DIY. Thanks!

Hey, I'm finding that after an hour or so of driving on a motorway at a steady 100km/h, the fuel ratios start leaning out from where I set them when at normal operating temperature after driving for 10miles (14.7), all the way up to 16+. This is the same behaviour that happens if I leave the car and get back in it again after it being switched on which leads me to believe it has something to do with the crappy air temperature sensor that is on the standard car. I am running twin map sensors but with the standard nissan temp sensor which I think I'm going to be changing. I'll write this up like I did with my AAC post. Is this behaviour happening because of heat soak or is it possible that there is something else happening? i.e. fuel temperature rising? I don't have a fuel temp sensor and it's not showing an option for specifying values in datalogit. I am thinking it is heat soak because I have a single turbo conversion with no turbo blanket.. yet, in combination with the crappy sensor. Any thoughts?

Hi, sorry to message on such an old post but I have a couple of questions as I've just bought one of these sensors to do some DIY myself. If I were to place this just after the intercooler, which is pretty cold, but the plenum still gets hot, would the air not heat up by the time it reaches the cylinders and get worse as the plenum gets hotter? I have water injection on my car so if I were to put the temp sensor before this, I would be, as expected, getting readings that are higher than what goes to the cylinder however this value would be constant when at WoT, thus tuneable for those cells; is my logic correct there? Many thanks!

Hi! So my next DIY project is to stop using the standard air temp sensor, which I believe is actually a water temp sensor. I actually read on this forum that the GM sensor is a pretty good alternative with a resistor in parallel (using powerfc so can't modify resistor values) if you can plumb it into an area of the system that doesn't get so heat soaked. Thinking just after the intercooler which is actually cold piping even after driving for many miles; in comparison to the hot to touch air intake plenum. I'm planning to do this in the next few weeks, so I will post a walkthrough of this like I did with my AAC cleaning. This should help the tuning process as currently, after driving 50miles/80km, I'm having to retune slightly because the AFR is getting a little leaner than I want. It's only 1AFR leaner, so sitting at around 15.7 instead of 14.7, but I'm quite picky. The reason for the heat is because I'm running a single GT4294R turbocharger that's non-ceramic with no turbo blanket/wrapping on the down pipe. The fuel lines and right hand side of the bay is heat wrapped well but this isn't really helping things with the air intake which does tend to get hot. This brings me to my next subject: - What are the thoughts on wrapping and turbo blankets? I hear that wrapping can cause cracks but haven't really heard anything bad about the decent turbo blankets. DEi are supposedly good manufacturers of turbo blankets but quite expensive. If anyone has any comments or suggestions on a type of turbo blanket, I'd be massively grateful!

Introduction I've always had problems with my idle on my r33 GTR running a power FC; it runs 264 cams and felt quite lumpy and often hunted for the right idle speed and AFR. I do the tuning myself but could never get the idle just right.. until today! This took me 4 hours to do but I am quite slow and I have quite a busy engine bay so I had to remove some things to get to what I was after. From what I have learned, there are two air control parts on a typical GTR, the IACV and the AAC. I'll show a picture and brief explanation of both: - AAC This is relatively easy to get to on the RB26; it is just underneath the intake plenum and has 4 bolts that are roughly 2 inches in length and are a 10 socket. It is comprised of two major parts; the electrical component which shows the AAC label and the controller which has the spring and screw inside which allows the fluctuation of air. As I understand, the AAC is designed to increase air flow when electrical load occurs, such as a power assisted steering wheel being turned. When this gets dirty, it can cause high idle because the spring holds the gap that lets the air in open causing a leak in the system which will also cause lean behaviour. Alternatively, if it's filled with gunk, it could cause hunting due to bad air fuel ratios from going too rich. See below for some pictures of me holding the AAC after I gave it a quick clean. (The AAC below is not my image) The AAC has a screw that you can turn; it is facing the front of your car or at the right of the right component on the above diagram. Turning the screw clockwise will lower idle and turning it anti-clockwise will increase idle. The basic functionality of this is that it overrides the system and leaves a small gap that air can go through. There is some conflicting instructions that to change the idle you have to unplug the throttle position sensor and/or disconnect the brown connection but you'll see what I did later on. IACV (Idle control valve) I'm not overly knowledegable about this component as I don't actually have this on my car. A lot of people remove this and/or block the piping and rely on tuning to do its job. It is located very much under the air plenum above the oil filter. Basically, this component will allow more air into the system depending upon how cold the water temperature is. As the water temperature rises, the valve will gradually shut until this device is no longer used. A couple of problems that I can think of is that if this is faulty and it doesn't close, there would be an air leak and if it doesn't open it would mean there would be some lean behaviour on startup if not corrected by the ECU.] The nissan skyline manual shows how to diagnose this if it's faulty but it is a real pain to get to. My experience I am fairly novice with cars but I'm learning more and more as I tinker around with my overly specced car that I bought on a whim one day because I felt my impreza wasn't powerful enough! So, I've had major problems with my idle; either hot or cold, it would start to drop below 800rpm and I'd have to apply the throttle to get it to stop it from stalling. I tried modifying the fuel ratios, the ignition timing and the idle settings on the powerfc using datalogit to no avail. After doing some research, I decided that I needed to take off the AAC and give it a clean to see if that would work. Required: - Size 10 socket wrench will do, it's not that tricky to get to like some people say; I had an ordinary sized socket wrench and managed to get to all 4 bolts easily AAC gasket or you can make one yourself using a stencil and some gasket material (You could re-use but I decided against it) RTV sealant Carb cleaner Phillips screw driver Toothbrush/pipe cleaner or some way of cleaning For a picture of the gasket, see below; it's quite tricky to find it and I had to get it from America and nearly ordered the RB25 one; I live in the UK. Instructions for removal: - Firstly, remove anything on the left side of the engine bay that will restrict you from getting just underneath the intake plenum; I had to remove my catch tank and my fuel pressure regulator to get to this but this took a few minutes as I'm always removing these to clean up on my overly obsessive cleaning schedule of my car. Remove the brown wire socket which is clipped on fairly trivially Use the socket wrench to undo each of the bolts; mine were so easy to remove that once I'd loosened each bolt, I could use my finger to unscrew which was a lot easier than worrying about dropping the bolts down into the endless pit inside the engine bay. Simply pull at the AAC gently, trying to rescue the gasket if you want to reuse; I found that it was just stuck to the AAC and was easy to peal off. Remove the air tube that connects to the left hand side of the AAC You should now be able to take the AAC out of the engine bay and take it to your working area ready to be cleaned. Half way through cleaning, I decided I was going to take some pictures but unfortunately I left my iPad at home so I had to use my laptop to take the photos. It was also very cold today and my fingers didn't like the combination of carb cleaner and freezing weather. Hard to believe they're actually normal looking when I'm in the nice warm area typing on my computer! The AAC is comprised of two parts; I call them the electrical component. They are joined together with two small phillips head screws and come apart quite easily. Be careful as there is a little rubber seal that sits between them: - and the air control component.. see below Mine was fairly dirty and had some black grimey gunk all around the spring and screw. I immediately smiled and was quite excited at the prospect that my lovely car was potentially going to stop idling badly! I got a spare toothbrush and pipe cleaner and used carb cleaner spray to basically rinse the whole thing out and clean the spring and screw out. This is a lot cleaner than it was but what you can see is two holes in the center of the air component. The hole on the left is the spring that is controlled by the electrical component and the hole on the right is the screw that you can manually screw with a phillips head screw driver. Make sure these are both clean before putting back together. I actually adjusted the manual screw so that there was a tiny gap as I've read that it needs to be open a slight bit. This could be wrong so this may need to be adjusted to meet your idle speed requirement. I also gave the electrical component a cleaning but only on the side where it connects to the air component. : - Once I had cleaned the air component, I scrubbed the port underneath the intake plenum with carb cleaner as there was a tiny bit of grime and old sealant. I then screwed the components back together to form the AAC again and then took my nice new gasket out of the packaging: - Applying the sealant Apply a very thin layer of RTV sealant on the AAC firstly by adding a small line, roughly 2mm thick in small sections and using my thumb to spread it out until the flat edge is completely covered. Place the gasket onto the AAC; it will only go one way so that the layout matches. If it doesn't match, you've probably bought the wrong gasket. It's quite easy to do as there is a lot of posts containing the RB25 part number and so on. Repeat step 1 but this time on the gasket on the side that will be attached back to the port The tricky part is now getting the AAC back on without fudging the sealant and getting into a right mess. I did this the first time but make sure that if you mess it up, you ensure the sealant is properly applied as if it is not, there could be an air leak. I found that with the sealant I used, the AAC actually stuck to the port without the bolts which was nice as it gave me the opportunity to let go of it to push each of the bolts in and hand tighten them before I used the wrench to tighten them. Remember to re-attach the pipe and brown connection which, for me, was quite easy. I thought it was going to be an annoyance trying to get them back on afterwards but they went on surprisingly easy. PowerFC idle learning (only for power fc) I did not adjust the screw on the ECU as I feel this is something that shouldn't really be messed with and I didn't change the throttle position screw. The only screw I set up was the one on the AAC which is shown above. I use datalogit but there are posts that let you know how to do this with the hand controller. Switch the ignition on and turn off any of the blowers/air con/lights etc. Reset the powerfc back to defaults but ensure that you've saved your map and can reload it with your preferred settings. Switch the ignition on and leave the car to idle for 10 minutes to learn idle at no load After those 10 minutes turn on the lights and the air blower for 10 minutes to learn idle at electrical load After those 10 minutes turn on the air conditioning for 10 minutes to learn idle at air con load The 30 minute period is required by power fc and should be performed, just for peace of mind after doing this as it can change quite a lot of things if the AAC was dirty. Hopefully this fixes your hunting idle; it fixed mine. Sorry for the lack of pictures and quality, as well as the inexperience that is obvious in this post. Just figured it would be nice to try and help people who have this issue as it can really be annoying stalling at junctions through no fault of your own!

I see, well I can get at them, I've got the tools to take them off and I'm hoping that cleaning it out may help the air con problem and the idle issues. Do you know if it is the brown plug or the TPS that needs disconnecting to adjust the idle rpm screw?

Thanks for that! So I am going to be cleaning both of those and checking the pipe work for problems. I'll also do an idle re-learn on the power fc. As far as unplugging the purple wire, I felt a little uneasy about that as I couldn't see why cutting out the air regulator would be a good idea. I can't see why nissan would put a part in whose problem can be solved by unplugging it lol. I guess I will have a go, I'm just not overly confident that I know what I'm doing so I don't want to be driving the car around with wires unplugged. Regarding the screw on the second image, I.e. The one I thought was the AAC, which has the AAC sticker on it, is it the TPS wire that I need to disconnect? I've read so many posts that say that it's the brown plug, some people saying the TPS etc, is there a definite answer for this on the rb26? I expected that if i turn the screw the idle speed will change, but when I was doing this, I had disconnected nothing.

Oh right, I see, ok well thanks for clearing that up. I'll report back when I get to work on the car.

Oh right, why does the second one state that it is the AAC on the sticker? I'm confused, sorry

Hey guys, Sorry for the delay in replying, I've actually been off on business and had to drop the car back in the garage. I've ordered the AAC gasket so I'm going to take that off and give it a good clean when I'm back but it won't be for a good week or so. I have a feeling that my AC issues/dodgy idle when cold is probably down to something around here as the electrics seem fine. I wonder if someone could clarify for me though: - http://img.photobucket.com/albums/v150/tegguy/002.jpg Is this the IACV? I thought that this was the cold air control valve - can this be taken apart and cleaned easily? http://i217.photobucket.com/albums/cc252/kagekispirit/TechNical%20Support/Rb26AACvalve.jpg This is the AAC and the part I just bought the gasket for and is the component that has the screw on it. I'm going to take this off and clean with carb cleaner until it shines!

Will get that to you asap, it's late here so I'll do it first thing tomorrow!

I'll take a picture of that and post it if that can help confirm? It's definitely going lean if I turn the screw anti-clockwise and not increasing the idle speed but there doesn't seem to be any additional piping down there. There's no vacuum leaks in the system either though as I had a smoke test run which held pressure very well indeed.

It's factory pipework I believe

Voltage to the ECU seems to be fine and I've connected the multimeter to the negative terminal and my earthing points on top of the rocker cover. Seems like the resistance is ok. I didn't expect there to be grounding issues as the wiring is very neat and tidy. I may have found the problem though; turning the screw on the AAC isn't actually doing anything other than making idle leaner. I was expecting that turning it counter clockwise would cause the idle rpm to rise but it's not doing that at all. I would assume that this would affect both idle and the air con system.

Alright, I'll have to get the multimeter out on this then. Datalogit is showing it sitting around 13.9-14.1, never anything more alarming than that so I never bothered. Are you suggesting there could be an earthing problem?

My idle is 1100 due to the 264 cams but does idle with a little instability at times. I will check the timing maps and re-check fuel cells although I can confirm that the fuel cell doesn't change when this happens. Infact regardless of whether the air conditioning is off/on or doing it's strange AFR behaviour, the cell stays constant if at the same load/rpm. I'll capture the following and post the results: - TPS value at throttle off and on and post the results Screen capture of the graph when the problem occurs I think there is something larger to blame here though as I'm finding that if I'm driving for long periods of time, the AFRs become leaner overall which brings the air conditioning spikes to 17+. Talking maybe driving for 50 miles+; air intake temperatures seem to be reading fine though so I can't attribute it to that.

Anyone have any further explanation for the air con causing such strange jumps in AFRs? It's literally, switch air con on whilst driving -> jumps from 14.7 to 15.1 -- sure, that's fine, but then it'll jump up to 16:1, then a few seconds later, back down to 15.1, then a few secs later, up to 16:1 again. I've kept an eye on the voltage and from what I can see, there's no noticeable change when air conditioning comes on. Still tends to just float around (13.9-14.1volts). As I wrote earlier, I guess the reason the AFRs are jumping is because of the compressor coming on and then going off to ensure the temperature inside the cabin remains stable but surely there's a way of stopping this ludicrous behaviour. I don't really like suddenly hearing the engine change tone every 5 seconds with air con on when it decides to run strangely lean. The issue is not apparent on boost as explained already but most certainly is apparent when attempting to just drive the car normally, i.e. not on cruise/boost.

I might pull the throttle plate this weekend and see if there is anything wrong here as even if I set a lower idle in datalogit, it still sits higher won't idle. I suppose that's a bit off topic but may explain why I have to add so much fuel at idle to hit stoich with air con on.

Eek, 800! This makes me feel really bad about the current idle. It sits at 1100rpm typically and I can't seem to get it any lower. I assumed this was because I was running 264 cams which I thought required higher idle and a richer idle condition. There's definitely not any vacuum leaks as I've tested this with a smoke test.

That is exactly what I do 89cal, I tune up all the time and pretty much drive with my laptop on the passenger seat. It's fun, I didn't known anything about tuning when I first got into Japanese cars but now I just enjoy monitoring it on the wideband. I'm not that bad at getting the AFRs right and I've got somewhat adept at tuning the ignition advance/retard too. Voltage is not changing when air con is on. I checked that as I can make adjustments to the injectors based on the voltage

Hey, no the O2 feedback and ignition timing adjustment for idle is off as apparently it is buggy. I guess the fluctuations I'm seeing could just be the compressor turning on and off when regulating the temperature. I may take the AAC off, give it a clean and see if I can play with the screw for a bit. It could be worth me re initialising the power fc and doing the idle relearning again too. Theoretically there shouldn't be this much difference between the AFRs.

I guess air conditioning correction is just a shortfall in the power fc ecu. It's somewhat strange to me though that there is such a difference between the air conditioning being on and off. I had to correct idle by enrichment to a load cell by quite a lot which can give me quite a rich condition on startup of the vehicle. Without the correction, idle would surge at around 17-18 AFR. I have cleaned the AAC but I don't believe that has much to do with air conditioning. It's just strange behaviour in my opinion. It's almost as if there is surging when driving with the air conditioning on, as it seems to fluctuate between 14.7:1 and 16:1 when cruising in sudden movements. The whole air conditioning side is something I don't really think I can tune if there is no way to make corrections.

Yeah, no problems at all under load; just as you say, on cruise. Yeah nothing higher than mid 15s usually but I thought that 16:1 at cruise would cause exhaust gas temperatures to get really high? I can adjust the idle rpm when air con is on and the mapping cell for idle air con also falls in a different zone so I can easily tune both values to idle nicely.

I've had the skyline a while now and I've been tuning the powerfc myself with fc edit/datalogit over the seasons to keep the AFRs where I want them. I've recently overhauled the fuelling as I wasn't using the throttle position vs injectors functionality. Supposedly a lot of amateur tuners will set the TPSvINJ to 1.0 and directly place values into the inj adjustments tab, which I believe is all you can do if you're using the commander. Anyhow, I've set up my throttle position curve and I've now been using the recalc base and have now got a much more accurate tune across the power band as I no longer have to add enrichment to areas that were once overly rich as the area would be touched when coming onto boost as well as cruising. Something I've never really got right though is the air conditioning! It's a right pain, my fuel map is perfect for what I want. I'm sitting at 14,7 on cruise and 14,3 at idle as my cams are 264s and don't seem to like sitting at stoichiometric. I come onto boost with AFRs of 12,5 and sit around 11,8 on max boost. The problem is if I'm just driving around normally at stoichiometric and then decide to turn air conditioning on, everything goes nuts! The AFR jumps to 15-16.. It seems calmer when in driving at steady throttle at high rpm, I,e, 100km/h / 62mph but still a lot leaner than I would like. So, with that said, and apologies for the wall of text above, can anyone help with the following: - 1. I've been led to believe that air conditioning is temporarily disabled when on boost, true or false 2. Is there any sensor value that I can use to determine when air conditioning is on and add enrichment to the mixture? I've looked at battery voltage, temperature, etc and just cannot seem to get it right. 3. Is this just a limitation of power fc and is the air con a problem for most people? Most tuned cars I see have had the air conditioning removed

Yes, will probably replace the system :-) Although! The one way valve should only be letting gases go back down into the exhaust and not up into it. Didn't quite understand what you said there