Sorry this is some what long. Trying to give all the info and I searched all over looking for things to check.

On cold start up, it doesn't hardly want to stay running and I know the ca has its cold start issues. After feathering throttle to keep it running and engine gets some heat, it will idle by itself, but it wants to idle way lean in 17-20 range. Trying to drive it before warmed up isn't possible because it is to lean still in the same range on wideband. Once its up to temp it will run/idle perfect at 14.7. Driving it will do fine too, cruising stays 14.7, on boost it feels good and 12.5ish. After driving, if I cut engine off and restart 5mins later it will go right back to running lean for a few mins, or i can drive it and baby it up to 2nd and hit boost for a second the afr goes back to being normal.

Last year before having to leave it sitting for a while, this issue was present, I checked codes then and there was nothing. Ill admit I haven't checked them again this go around, but I will next time I get a chance to mess with it. Had vacuum leak at IACV gasket last year, fixed it and cleaned valve, which helped a lot with idle once it warm. Fuel pressure was set at 36psi without engine running, never checked it while it was running. I know in closed loop it can compensate for vacuum leak, and I've checked for one with the brake cleaner method with no luck. Coolant temp sensor was swapped from my old ka after having no start issues in cold and it fixed that issue, but still probably going to buy a new one. My o2 sensor isn't the bosch number, but it's one that crossed with that number, only difference was the one I got is skinny compared to the bosch being fat type. Not sure what else to check besides maf and finding a different way to look for vacuum leak.

It sounds like the heater circuit in the O2 sensor isn't warming the sensor up like it should. If that's not working, the ECU will try to go into closed loop, but the O2 sensor won't read correctly, and it throws things off. The O2 sensor should be hot to the touch within a minute of starting the engine. Maybe try ohm'ing out the heater circuit?

Well I just checked the FSM and there's no resistance range for the heater in the O2 sensor heater circuit.

Ill check to see if its getting warm. That still doesn't make sense completely though that once the engine is warmed up it could idle all day and be fine but as soon as I cut it off and restart it a couple minutes later that the o2 cooled off enough and takes another 10 minutes before the car runs right, unless I hit boost once for just a second. Hopefully this weekend I will get some time to mess with it and check for codes again.

You'd be surprised how fast egts drop. On my SOHC KA, it didn't have a heated O2 sensor and if it idled for too long, the sensor would get too cold and it would fall out of closed loop.

Well it's something new to look for so I will give it a go.

Well looks like I won't have a fix to this for a while now, messing with it today I heard some good ole rod knock and only have a few hundred miles on the engine, oh well.

Craaaapppp. That sucks. Did you rebuild it yourself?

Nah, I got it from Dee, but I'm certain it wasn't his fault. This thing has given me issues the whole time. First was 2 dead injectors for cyl 2 and 3. Next was a bad CAS that wouldn't fire cyl 1. Once that was all fixed and it was running, my boost gauge was messed up and found out wastegate actuator was adjusted wrong. With new working gauge it was over 15psi(gauge only goes to 15 since i only planned to run 10-12) on the t25. I drove it too long and hard with it like that, so I'm gonna say the overboost and fuel cut/pre ignition beat the bearings and it finally gave.

Ouch! Yea, that would do it.

Alright I finally got this thing back together and running. Still having issues with it wanting to lean way out warming up(18-19's on wideband). Going to check to see if o2 sensor is getting warm this weekend. On the o2 sensor I'm thinking the one I have doesn't work. I didn't get the bosch, I got another one that the bosch number crossed over to which fits z31. The one i have is skinny and i know the bosch is fat, so i'm wondering if that's part of my issue. The only other things I can think is a faulty cts and I'm pretty sure my cold start valve isn't working since I don't have a fast idle and it will usually run at 13.5-15.5afr when I hold throttle at 1500ish during warm up. The engine runs great once its up to temp, minus a few stumbles here and there when its trying to level out after some harder pulls.

Yea, I'm pretty sure the stock EMS expects a heated O2 sensor, so if you're using a single wire, that won't work properly. Bad CTS will cause issues as well. Bad cold start valve will definitely cause it to run really poorly when it's cold too.

well its not a single wire o2, its 3 wire and connector matches engine loom, the only thing is that mine is a skinny type and i know the bosch is fat. Checked the o2 this weekend though to see if it was getting warm with key on and it isn't so going to order bosch one along with nissan cts. I cleaned my cold start valve best I could with brake cleaner, its the round one, which didn't change anything. Will start looking for another one of those too.

Hmm, yea, something doesn't sound right with the O2 sensor. It should get hot.

I've never cleaned a cold start valve and had it work. I've always had to just replace them.

Got a bosch o2 over the weekend and it never got warm with key on, but after putting it in my af didnt flauctate as much as before. Put a nissan cts in today which of course made it start a lot faster than it was. Have to find a cold start valve now, pretty sure it done for. Idle is super low on first start up,500-700, and af is 17.5-18.5. When I hold rpms up to 1200ish af is like its suppose to be at about 14 and then once it's warmed up the car is perfect at 900 and 14.7. Thanks for the help float.

Yea, cold start RPM should be around 1500rpm and then slowly drop over the next minute or so.

It's called an air regulator BTW. You order the part from an SE-R Sentra

confirmed-air-regulator-replacement-t560987.html

Bumping this because im still having issues with getting this car started. Drains my battery every time i try to start from cranking so much. Checked fuel pressure and it is still 37-38psi even while cranking. Tried another new nissan CTS, no change. It's a fueling issues of some kind, haven't pulled fuel rail yet to make sure inj are spraying(but as i said in thread before, once it warms up it runs fine), they are getting signal and can hear them clicking. Fires right up when i spray starting fluid in it, but as soon as its burned that off dies, sometimes im able to keep it running by feathering throttle in the 2500rpm range. I could have a vacuum leak but that seems like a pretty massive leak i would have found when i do get it running, and i have yet to find one. Going to do a compression/leak down here in the next week if i can. Any other ideas what to check?

No codes? If not, could be bad MAFS. Do you have stock injectors? If so, you might try unplugging the MAFS and see what that does.

No codes, never set one before. Stock inj and ca MAF. I tried unplugging MAF with no change. Was able to get started this weekend while it was warmer out. Checked uncorrected AFR with o2 unplugged and it had a steady 16.5, so vacuum leak somewhere most likely, but not big enough to cause this hard starting that should be pretty noticeable. I've tried looking for leak before with no luck finding it the brake cleaner way. Vac lines have been simplified so there isn't a lot. I've leaned towards MAF but it doesnt act like most with limp mode and unfortunately I'm the only ca around my city i know of so i can't borrow one to try.

Where is your MAFS located? Not having it located correctly can cause all kinds of strange issues, but won't ever throw a coffee. 16.5 is pretty lean. Should be closer to 12 with O2 unplugged. What about the coolant temp sensor? Have you tested it? Ifb it's not reading correctly, it can throw your AFR'S off and make it hard to start?

I just reread this and see you've tried multiple CTS's, so nevermind that. Did you get the cold start valve replaced?

Yeah I have done 1 aftermarket and now 2 nissan CTS. The maf is in stock location, just have the PBM intake tube and a cone filter. Hoping to do compression and leak down this next weekend. No I never got the valve replaced, I put it off when it got colder and couldn't even get car to start. That valve is only for fast idle though isn't it?

Yes, it's only for fast idle, but CA's are INFAMOUS for being nearly impossible to cold start when that valve isn't working properly. I have lots of personal experience with it as well. It can get quite cold in Kansas and back when I was still using the stock ECU and associated hardware, my CA had a TERRIBLE time starting in the cold. I'd often run the battery dead and still never get it to start. Once I replaced that valve, I never had another issue.

Well damn. Yeah I read ca's were bad about cold starts before I ever got the engine, just didn't think it was to this extent. Guess I will get around to replacing the valve and see what happens. I still think there is something else off with how lean it runs.

There may be something else up, but you may never find it if that valve isn't working. I'd start there. I don't think they're terribly expensive, but I think you have to remove a coolant house to get it out. It's been a while, so I could be wrong.

You are probably right about that. Gonna get it ordered at end of the week. Will check back once i get it on.

Please keep us updated so other people who have the same issue may find help with this thread, thank you!

Well, looks like I found the problem. The cold start valve came in, and got it on. Still did not want to start. Messed it it for a while to get it barley running, still doing its 17-19 afr, and decided to try unplugging the MAF again to see if it would idle with new valve. Sure enough it fired right up and idled at 1200ish and afr was around 12. So on to find a good maf

Great! It sounds like you've got it narrowed down. I MIGHT have one in the garage, but it can't promise if it's any good. If you can't come up with a known good one, let me know and I'll scrounge around in my stockpile and see if I have anything.

MAF came today and what do you know, it will idle by itself smoothly while warming up with a 12.5-13 afr. Also no longer runs lean if you cut it off and restart it warm. I'll update the first post in a bit so the whole thread doesn't have to be read through. Thanks for the help float.