Cold Start Issue

[QWK32]

sorry, lol

ok, those links you have put up, one is for cleaning the AAC valve, which all the RB motors have. it controls/stabilizes engine rpm during normal idle, cold start, when the air conditioner is turned on, etc.

the second link you put up is for the Air Regulator, which is on the RB20. this valve also helped to stabilize idle and with cold starts. i dont think any of the other RB engines had one. the RB25 NEO doesn't. you can check to see if this is also the case with the R33/S1 by looking under the throttle body and see if you can see an Air Regulator valve like is shown in the second link you posted up, but i think its just a thing they had on the RB20.

so on the older RB20 there were 2 valves to control idle. on the newer RB25's there is only one valve to control idle, nissan just left the AAC valve to do all the idle control. the AAC valve is also refered to as the IAC valve.

so if you want to clean the valve that controls idle clean the AAC valve on the back on the inlet manifold (the first link you previously posted). but keep in mind that this valve is designed to control/stabilize idle on an already running engine. you may get a better start after cleaning it, but the main reasons you clean the AAC valve are, if your idle is too high or too low, or if you engine idle hunts around, say it jumps around between 600-1200 rpm for example. you idle is low, as in its barely turning over, thats too low for the AAC valve to recover.

p.s. i know the exact problem you have, my old 32 used to do it, i cleaned all these valves and it didn't really help it, still had to tap the accelerator to get it going.

Edited August 5, 2009 by QWK32

[_Ryan_]

sorry, lol

ok, those links you have put up, one is for cleaning the AAC valve, which all the RB motors have. it controls/stabilizes engine rpm during normal idle, cold start, when the air conditioner is turned on, etc.

the second link you put up is for the Air Regulator, which is on the RB20. this valve also helped to stabilize idle and with cold starts. i dont think any of the other RB engines had one. the RB25 NEO doesn't. you can check to see if this is also the case with the R33/S1 by looking under the throttle body and see if you can see an Air Regulator valve like is shown in the second link you posted up, but i think its just a thing they had on the RB20.

so on the older RB20 there were 2 valves to control idle. on the newer RB25's there is only one valve to control idle, nissan just left the AAC valve to do all the idle control. the AAC valve is also refered to as the IAC valve.

so if you want to clean the valve that controls idle clean the AAC valve on the back on the inlet manifold (the first link you previously posted). but keep in mind that this valve is designed to control/stabilize idle on an already running engine. you may get a better start after cleaning it, but the main reasons you clean the AAC valve are, if your idle is too high or too low, or if you engine idle hunts around, say it jumps around between 600-1200 rpm for example. you idle is low, as in its barely turning over, thats too low for the AAC valve to recover.

p.s. i know the exact problem you have, my old 32 used to do it, i cleaned all these valves and it didn't really help it, still had to tap the accelerator to get it going.

correct but apparently there is also a cold start valve under the plenum, in the RB25 guide and according to 2mechanics.

[kidafa]

ok so theirs no real point cleaning the back valve as its idling sweet once its going.....

Ryan when are you going to hunt it down on your car?

what shall i do

[TR34SON]

had the same problem with my r34 GTT. turns out it was the spark plug spacings. weird but worked a treat.

[66yostagea]

had the same problem with my r34 GTT. turns out it was the spark plug spacings. weird but worked a treat.

I'd rather clean the AAC (IAC) before doing the plugs. Need that front facing plenum.

No wonder my first thread did not get going. This is mass confusion.

Edited August 5, 2009 by 66yostagea

[BensDR30]

lol!

I haven't checked in FAST, but I am assuming that the solenoide adjacent the AAC/IACV is some kind of FICD?

If so, that may be worth checking too, as it may be active during cranking.

When my S1 was acting in a similar manner (including the idle dropping right off when slowing to a stop - even on a hot engine) I looked at 3 things;

The O2 (which was known as dodgy, and replaced)

The plugs (which were 'compliance' Autolite and replaced with NGK Platinums)

The AAC (but I only removed the control motor from the housing via the 2 screws & gave it a wipe over)

The symptoms of a slow cold idle, flaky hot idle, and occasional cold stall were cured.

In the last couple of weeks I have had a momentary slow cold idle occur once or twice - but that could be due to me letting go of the key a fraction too early. I may check the AAC to see if it has gummed up, but can confirm that it is providing a wide range of engine speeds via testing through Consult control (the opening can be manually set in DataScan).

PS Chris, I'll probably only work a 1/2 day tomorrow, so should be around in the arvo if you want to look at your car then.

[QWK32]

lol!

I haven't checked in FAST, but I am assuming that the solenoide adjacent the AAC/IACV is some kind of FICD?

If so, that may be worth checking too, as it may be active during cranking.

i think your right there Ben but looking at this diagram it says it is activated by the A/C.

[BensDR30]

Fair enough - I'm without technical resources right now

(I expected the air con to be the only situation, but couldn't be sure)

An Air-reg is certainly shown on that diagram, and they are there only for cold running - I thought that the AAC/IACV had completely replaced that function, but it seems it's still used on some '25's at least...

If your air-reg is crook (jammed closed), then you won't get a fast cold idle, declining over time as the bimetallic strip closes the port.

If it's jammed open, then the idle will be too damn fast when warm.

I'm considering disconnecting the Air-reg heater on my FJ, as the idle drops of a little too fast when it's stone cold.

[QWK32]

An Air-reg is certainly shown on that diagram, and they are there only for cold running - I thought that the AAC/IACV had completely replaced that function, but it seems it's still used on some '25's at least...

yes, and on the same style diagram in the R34 workshop manual the Air regulator is apart of the AAC. so the R33/S1 RB25's still have a separate air reg but on the Neo RB25's it has been combined with the IAC-AAC valve.

Edited August 5, 2009 by QWK32

[66yostagea]

AFAIK the S1 Stagea RB25DET has the R33 Series 2 engine. Does this make a difference?

I am thinking that maybe the best way to go is Diagnostic.

[_Ryan_]

ok so theirs no real point cleaning the back valve as its idling sweet once its going.....

Ryan when are you going to hunt it down on your car?

what shall i do

Either when I have time or the wallet recovers from two lots of reg and one lot of insurance and one lot of fixing a 32 is done

lol!

I haven't checked in FAST, but I am assuming that the solenoide adjacent the AAC/IACV is some kind of FICD?

If so, that may be worth checking too, as it may be active during cranking.

When my S1 was acting in a similar manner (including the idle dropping right off when slowing to a stop - even on a hot engine) I looked at 3 things;

The O2 (which was known as dodgy, and replaced)

The plugs (which were 'compliance' Autolite and replaced with NGK Platinums)

The AAC (but I only removed the control motor from the housing via the 2 screws & gave it a wipe over)

The symptoms of a slow cold idle, flaky hot idle, and occasional cold stall were cured.

In the last couple of weeks I have had a momentary slow cold idle occur once or twice - but that could be due to me letting go of the key a fraction too early. I may check the AAC to see if it has gummed up, but can confirm that it is providing a wide range of engine speeds via testing through Consult control (the opening can be manually set in DataScan).

PS Chris, I'll probably only work a 1/2 day tomorrow, so should be around in the arvo if you want to look at your car then.

Yeah, cleaning the IAC would fix the stalling when braking issue... but not cold start.

[kidafa]

must thank Ben massively to coming over and plugging into my stag today with datascan.

Nothing seemed out of the ordinary which is good, but we couldnt find the cause 'cos of this. Might give the two vavles a clean in the not to distant future to see if it clears up. Its not going to be cold for much longer anyway so I might just wait.

Once again thanks Ben, was good to put another face to a user name

[BensDR30]

Only too happy to help - and wouldn't you know it; After flushing the coolant and replacing the thermostat tonight (preventative maintenance), my car ran slow and stalled on the first start...

The second attempt was a slow runner too, but it picked up.

Jinxed!

[kidafa]

maybe ive given you the bug, as my first start this morning was slow but it recovered

[BensDR30]

Mine was shite today too - and I was watching the Consult data when I started it to see what was going on.

The AAC went to 99 (full open) during cranking and below normal idle, but it wasn't enough... I started the car again and noticed that even once it did flare it was only at ~1100rpm, so I'm leaning towards the air regulator being partially closed (AAC kept it going at a value of 80 the 2nd time). So the next time I'm feeling like hurting my hands and lamenting how easy it would be to remove with the engine out, I'll try to test & clean it!

[JAP-JET]

Did you sort your issue out? I was having the same issue with mine for ages, put the factory bov's back on and it seemed to fix it, but when i put the aftermarket items on the car i never blocked off the pipe that fed into the intake pipes which im guessing was the problem sucking more air into the engine than the the two afm's were reading. As mine is an autech it may not be the problem your suffering but might be a thought for you to check, if you have put aftermarket items on the car.

Ads

[BensDR30]

It's an intermittent issue for me, and generally not a major problem. On the coldest mornings, I simply hold the start position for a fraction longer to have a higher cranking speed. That seems to fix it (I'm used to the work car which effectively has a start switch, so 'cranking' a car until it starts isn't something I do very often )

Any intake leak will cause incorrect AFR's and poor running. I'm happy I don't have any such leaks.

[66yostagea]

I never got to fixing, and now the weather is warmer it starts fine.