Just try this: unplug your PCV from the air intake, and make sure you block the intake. Just for this test, vent the PCV to atmosphere.
Try the test again and see what it does.
Try the test again and see what it does.
D40 idling high - SOLVED
- Thread starter nismo4x4
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nismo4x4
Member
It should be the blue one, which will lead back to the top of the camshaft cover at the rear of the engine.
Yes to the MAFS. Give it a clean - just be gentle, it's $400 worth of sensitive. Only spray stuff into it - don't poke it. Inside is a thin wire that is easily damaged.
Yes to the MAFS. Give it a clean - just be gentle, it's $400 worth of sensitive. Only spray stuff into it - don't poke it. Inside is a thin wire that is easily damaged.
nismo4x4
Member
Hi tony...sorry its taken this long but i have recently done your test and its still idles high...
i also took it to nissan who kinda had no idea but did find an injector cable been chewed by "rats" which they replaced for $130 and still idle highs
could it be the fuel rail pressure sensor??
It could be the sensor. I'm glad it's not the PCV, that means you're not getting overrun.
The problem with the pressure sensor is that the thing sits in the fuel rail and Nissan won't sell you one without the fuel rail. It's around $4K from memory - but I do recall someone managed to finagle one without the rail itself and it cost a fraction of that.
The sensor can be tested, there's a procedure for that in the manual, take a look at p1106 of EC.PDF in the electronic manual. There is a problem that I can see with the routine though - it's looking at the return value, which it also gives a significantly large "acceptable" range for. I'll have a look at what my car's free-revving fuel rail pressure is reporting as tomorrow, I know idle (750rpm or so) is around 4400psi. I'll rev it to 2000rpm and let you know what my rail pressure is for that - it should give you an idea of whether your sensor is reporting the right levels or not.
If your sensor is out, there's a good chance that sooner or later your ECU will decide that you have a fuel leak, or something else wrong with the fuel system that's causing the erroneous pressure readings - based on a calculation of throttle position, engine RPM, engine load - there's an expected fuel flow rate range and your engine might be outside that.
The problem with the pressure sensor is that the thing sits in the fuel rail and Nissan won't sell you one without the fuel rail. It's around $4K from memory - but I do recall someone managed to finagle one without the rail itself and it cost a fraction of that.
The sensor can be tested, there's a procedure for that in the manual, take a look at p1106 of EC.PDF in the electronic manual. There is a problem that I can see with the routine though - it's looking at the return value, which it also gives a significantly large "acceptable" range for. I'll have a look at what my car's free-revving fuel rail pressure is reporting as tomorrow, I know idle (750rpm or so) is around 4400psi. I'll rev it to 2000rpm and let you know what my rail pressure is for that - it should give you an idea of whether your sensor is reporting the right levels or not.
If your sensor is out, there's a good chance that sooner or later your ECU will decide that you have a fuel leak, or something else wrong with the fuel system that's causing the erroneous pressure readings - based on a calculation of throttle position, engine RPM, engine load - there's an expected fuel flow rate range and your engine might be outside that.
nismo4x4
Member
Many thanks for your efforts Tony. I am very appreciative. in the past month its gone into limp mode 5 times...as i was just dealing with the high idle it didnt really bothered me but now since limp mode kicking in...i better get it sorted...i have also noticed if the revs are sitting at 750 thinking everything is ok sometimes when i put it in any gear the revs jump to 1200 then putting gear back in neutral revs back at 750 wtf
i dont have a consultII device...but i do have a multimeter which i can check the voltages etc
also while back i disconnected one earth point that bolted to the battery tray which the cable continued to the engine block, thinking the engine block should suffice earth point...as i placed a cat battery in and the earth cable was to short...not sure if that limited the earth out dramtically causing issues??
i dont have a consultII device...but i do have a multimeter which i can check the voltages etc
also while back i disconnected one earth point that bolted to the battery tray which the cable continued to the engine block, thinking the engine block should suffice earth point...as i placed a cat battery in and the earth cable was to short...not sure if that limited the earth out dramtically causing issues??
The engine block is a major earth point and the cause of significant troubles with anything ranging from alternator charge rate, glow plugs, injectors, starter and the numerous sensors.
If it's behaving oddly in neutral it could be the NPS although I wasn't sure that was ever an issue in the D40s. Here's something to try though: start the car in neutral and notice the idle @ 750rpm. Now, put the car in first, do NOT release the clutch. Idle speed? If idling high, push the gear lever to the left (leave it in first, you're just pushing the lever sideways in the 'first gear slot'). Doesn't matter left or right, do both - but does THAT change the RPM? If so, it's definitely a neutral position switch thing in the gearbox, but I'm wondering why it's raising the RPM. The D40 shouldn't do that.
I'd also go past all of the injectors and rip the electrical connection off - I wouldn't use plastic explosives, mind you, something a little gentler might be cheaper in the long run. Put them back on, this will help clean the injector contacts. Do the same for the pressure sensor's connector, take it apart and put it back together (repeat 2 or 3 times if they look dirty inside).
If it's behaving oddly in neutral it could be the NPS although I wasn't sure that was ever an issue in the D40s. Here's something to try though: start the car in neutral and notice the idle @ 750rpm. Now, put the car in first, do NOT release the clutch. Idle speed? If idling high, push the gear lever to the left (leave it in first, you're just pushing the lever sideways in the 'first gear slot'). Doesn't matter left or right, do both - but does THAT change the RPM? If so, it's definitely a neutral position switch thing in the gearbox, but I'm wondering why it's raising the RPM. The D40 shouldn't do that.
I'd also go past all of the injectors and rip the electrical connection off - I wouldn't use plastic explosives, mind you, something a little gentler might be cheaper in the long run. Put them back on, this will help clean the injector contacts. Do the same for the pressure sensor's connector, take it apart and put it back together (repeat 2 or 3 times if they look dirty inside).
nismo4x4
Member
Hi tony,
thanks for getting back to me
I have tested the NPS and all seems good. no idle change at all when moving in any gear...only idle changes when moving back to neutral
i pulled all 4 injector plugs few times and placed back in aswell as the FRP plug...i did not remove the pressure sensor, which i might do when back at home.
even tho i cleaned the MAF sensor i heard they can still be faulty...so i pulled one from a mates d40 and tested mine in his and vice versa...no change my maf worked fine in his and his maf in mine still idled high...
nissan said that my battery needs replacing as it was testing 7 volts...so when i tested it was 12.5V and with car on 14v as expected...it did drop to 8volts when cranking though...unsure if thats what they were talking about but id assume voltage would drop during cranking
I might try testing his FRP sensor before buying one. ebay does sell them just the sensor thankgod
pulling me hair out...and i dont have that much left...
thanks for getting back to me
I have tested the NPS and all seems good. no idle change at all when moving in any gear...only idle changes when moving back to neutral
i pulled all 4 injector plugs few times and placed back in aswell as the FRP plug...i did not remove the pressure sensor, which i might do when back at home.
even tho i cleaned the MAF sensor i heard they can still be faulty...so i pulled one from a mates d40 and tested mine in his and vice versa...no change my maf worked fine in his and his maf in mine still idled high...
nissan said that my battery needs replacing as it was testing 7 volts...so when i tested it was 12.5V and with car on 14v as expected...it did drop to 8volts when cranking though...unsure if thats what they were talking about but id assume voltage would drop during cranking
I might try testing his FRP sensor before buying one. ebay does sell them just the sensor thankgod
pulling me hair out...and i dont have that much left...
Here's something dumb to try. Get some jumper leads and connect the battery negative to the engine body with them.
7V while cranking is a little low, so's 8V. It's supposed to be able to maintain 10+ while cranking, it means the battery has insufficient strength to crank properly. That could upset the ECU but you'd think it'd get over that. Try your mate's battery?
What's your rail pressure at idle?
7V while cranking is a little low, so's 8V. It's supposed to be able to maintain 10+ while cranking, it means the battery has insufficient strength to crank properly. That could upset the ECU but you'd think it'd get over that. Try your mate's battery?
What's your rail pressure at idle?
nismo4x4
Member
hey the neg battery terminal is currently on the engine block...do u want me to kind of double up??
will try another battery...not hard...i did previously test the cranking on my mrs Captiva and only dropped couple volts (10-11V)....could be the battery...
unsure how to test the rail pressure??
will try another battery...not hard...i did previously test the cranking on my mrs Captiva and only dropped couple volts (10-11V)....could be the battery...
unsure how to test the rail pressure??
Rail pressure is reported by the ECU. I was interested to see if it jumped in neutral. You can use a bluetooth OBD adapter and the Android Torque app to get the info.
I asked about the battery because you'd mentioned taking an earth point off, I just thought if you temporarily put a good "earth bridge" in place to restore that connection, it might reveal an inadequate earth. If it's there and you're confident in it, all is good, time to think of something else - although to be honest, I'm running out of ideas too.
I asked about the battery because you'd mentioned taking an earth point off, I just thought if you temporarily put a good "earth bridge" in place to restore that connection, it might reveal an inadequate earth. If it's there and you're confident in it, all is good, time to think of something else - although to be honest, I'm running out of ideas too.
nismo4x4
Member
OMG Tony mate its FIXED!!!
turned out to be me CAT battery...i connected the jumper leads to the mrs car and started the car without the high idling...disconnected jumper and retested 3 times with and without jumper leads and each time with leads on the idled was perfect...
so turns out nissan was correct and that while cranking the car the voltage must not be below 10v
.
wow i can lay in bed now and not think about the ol nav
MANY MANY thanks Tony for your input mate...always helpful.
turned out to be me CAT battery...i connected the jumper leads to the mrs car and started the car without the high idling...disconnected jumper and retested 3 times with and without jumper leads and each time with leads on the idled was perfect...
so turns out nissan was correct and that while cranking the car the voltage must not be below 10v
.
wow i can lay in bed now and not think about the ol nav
MANY MANY thanks Tony for your input mate...always helpful.
That's excellent news! It sure is a stumper though - who'd have thought that a high idle would be caused by a battery that is on the way out? I mean it leaves ya a little bit 
but as long as it's sorted that's great!
but as long as it's sorted that's great!
