Idle hiccup

[ToroGTS]

Abd the iacv is always adjusted when the engine is cold, the iacv let's more air in when the car is colds and closes once it warms up a little bit.

The reason why a car with a blocked off iacv doesn't idle well on cold start you need to be on the gas for the first minute or so, your foot on the gas is acting as the iacv technically, and hopefully better coilpack will also help the hesitation

........ you are talking about the auxillary air valve that is in the valley above fuel rail. idle air control valve is on the back of the intake mani close to fire wall, is adjusted at operating temp and actively compensates for loads applied eg. A/C compressor and changing alternator voltage among other things.

Remove your IACV and clean it out, it may be gunked shut as it should definitely respond to the adjustment screw. You may have a good size vacuum leak, bad o2 sensor, bad or dirty MAF sensor (remove your air filter and clean the MAF hot wire gently with throttle body cleaner), or the black smoke could be the result of incomplete combustion from bad coil/plug/ignitor. Also check that you have a good vacuum line to your fuel pressure regulator with no leaks. May be worth the $40 or so to get a in line pressure gauge on your fuel line. TPS could be an issue for idle speed but not richness as it primarily affects ignition timing advance. Probe the middle pin on the connect coming form underneath the TPS (not the connector right on TPS sensor) other multi meter lead going to a ground and look for something in the range of 0.46 v closed throttle to ~4.0 v wide open throttle, with a smooth increase of voltage as throttle opens. Skym's advice above is sound.

[Skym]

AACV is located on the back of top half of intake manifold (facing firewall). AACV is adjusted by ECU to raise idle rpm to 1000rpm when auxiliaries like aircon is on, steering wheel is turned which raises rpm, etc, hence "auxiliary" in it's name.

IACV just has voltage into it (+ and -) and is activated by engine heat (can test it by putting it on a hot plate and valve inside should close within I think was around 9 minutes or so and if doesn't close fully it needs replacing or cleaning), hence why it's located on top of bottom half of intake manifold (close to engine / heat source). Once this valve is closed it's not used anymore.

Up until early 80's Nissan had a manual choke on dash that does the same job as the IACV (have been in a Nissan Sunny? with this manual choke). IACV is just an automatic choke (allows car to be driven while engine is warming up). I always warm engine up on the spot before driving, I guess habit of the days of when manual chokes were around.

TPS is like a electronic version of an accelerator pump if used to working on old school carb engines.

[Frankyy]

AACV is located on the back of top half of intake manifold (facing firewall). AACV is adjusted by ECU to raise idle rpm to 1000rpm when auxiliaries like aircon is on, steering wheel is turned which raises rpm, etc, hence "auxiliary" in it's name.

IACV just has voltage into it (+ and -) and is activated by engine heat (can test it by putting it on a hot plate and valve inside should close within I think was around 9 minutes or so and if doesn't close fully it needs replacing or cleaning), hence why it's located on top of bottom half of intake manifold (close to engine / heat source). Once this valve is closed it's not used anymore.

Up until early 80's Nissan had a manual choke on dash that does the same job as the IACV (have been in a Nissan Sunny? with this manual choke). IACV is just an automatic choke (allows car to be driven while engine is warming up). I always warm engine up on the spot before driving, I guess habit of the days of when manual chokes were around.

TPS is like a electronic version of an accelerator pump if used to working on old school carb engines.

Thank you, so like I was saying iacv is adjusted when the car is cold, the iacv is not used at all when the car is warmed up, after warm up the idle is adjusted by the throttle plate if that doesn't lower it enough you have a vacuum leak somewhere or throttle body leak.

Take iacv out and give her a very good cleaning to start off, my 1997 rb26 had a clogged up iacv with only 20k km

[ToroGTS]

I've removed my cold start valve (IACV as we are supposedly calling it) all together with all around benefit to A/F tuning and no noticeable effect.

http://www.ebay.ca/sch/i.html?_nkw=r32+nissan+skyline+Idle+air+control+valve&_sacat=0&_odkw=r32+nissan+skyline+IACV&_osacat=0&_from=R40

http://www.ebay.ca/sch/i.html?_nkw=r32+nissan+skyline+cold+air+regulator&_sacat=0&_odkw=r32+nissan+skyline+cold+auxillary+air+valve&_osacat=0&_from=R40

[Frankyy]

if the car is daily driven, or driven is very cold temperature then I wouldnt remove it but I only hear good things about people removing their IACV, if you can delete the vac lines going to it that eliminates another possibility of a parts failing

[krystalized_jdm]

It is my summer DD, I was also advised to disconnect TPS when adjusting the iacv.

I am going to see if I can get it to run better, and i'll be back with the results.

[krystalized_jdm]

Started up fine, ran at about 1800 like it used to (put screw to around where it was before tampering with it)

Noticed some what smoke coming from near the exhaust manifold, that went away within a minute of starting.

After running for about 2-3 minutes. It reved down to about 1100 but it was not stable. (was jumping from 1k-1.2k approx)

Pushed gas a bit, reved like normal and a few seconds later engine started chugging again. (TPS was disconnected still)

Most likely going to end up taking this to a shop, I'm sick of this and I have no clue how to go about fixing it.

Edit - I am re-reading all of these problems that you guys say could be the issue, but why would this be an issue only AFTER adjusting the AACV? Car ran 100% fine (with the exception of the hiccup) prior to this. Now I can barely get the damn thing to run.

[Frankyy]

your car idling high hides the true issue with the car, try a working MAF?

the first thing to diagnosing a problem is getting the car to idle around the RPM that it should be originally, then you go from there, if the car can't idle properly at 800-900 and you raise the RPM your only hiding the problem,

lower the RPM down to 800-900 and go from there, a bad maf could very well be your issue, don't rely on the simple" if you unplug your maf that means it's good" that only means your getting a signal back, doesn't mean it's 100% operational

do a little reading and see if any of these issues relate to yours

http://forum.r31skylineclub.com/index.php?topic=154573.0

just google, rb20 hunting idle tons of result

edit: it ran fine but at 1800RPM correct?

[krystalized_jdm]

Figured out the stalling issue, looks like one of the intercooler pipes was disconnected and it flukely happened when I was adjusting.

I feel stupid for having an issue like this.....

Anyways, yes I agree the high idle is hiding a problem with my car.

I was unable to adjust the idle with the IACV, it wouldn't change when i adjusted screw. I am goign to remove iacv and clean it and see if it helps.

[Frankyy]

glad theres progress beeing done! keep us posted!

[krystalized_jdm]

Haven't touched the IACV since last post, I did however get the exhaust mounted, bolted and put on.

Since then, the idle "hiccup" has turned into a misfire (or so it sounds)

After driving it, hitting boost at WOT it misfires, if I hit about 1/4 way throttle and hit full boost it runs smooth. Thinking I am having a fuel issue, as if it was incomplete it would be getting some amount of backfire?

The high idle kind of fixed itself, it runs at 1200 and I am happy with that for the time being.

[Skym]

When MAF is unplugged, stock ECU uses a preset voltage value for MAF input, so engine can be started and ECU engages a revlimiter.

Intake airleak near MAF can cause a stutter (similar to missing coilpack), or have faulty coilpack.

Most of the time I find intake airleaks cause idle instability. Sometimes it's caused by o2 sensor making ECU make engine run leaner than it should (lean missfire), combined with gapped down spark plugs. A long run on motorway usually cleans spark plug tips and engine idles smooth.

Also spark plug electrode can get damaged when regapping them (buy cheaper NGK copper spark plugs, regap them).

[krystalized_jdm]

Gap was done by the person who sold it to me.

I will run my consult via laptop and see what I get for MAF voltages when I fluctuate throttle/boost etc.

There is no leaks near maf. Intake is sealed, and the extra 2 pipes that go into the rubber intake hose are clamped 100%.

I unplugged o2 and it ran a bit smoother but still a little off. I bought new o2 sensor, and fuel filter. I will replace them both and see if I see a change.

[Skym]

Service engine, replace spark plugs, oil, filter if it has sat for months.

Also check cat, could be partly blocked, usually had it after around 80,000kms. Would explain when opened rear of exhaust up, why engine ran better.

[krystalized_jdm]

plugs are replaced, oil filter and fuel are being done soon.

How can you check for plugged cat?

Edit - Couldn't get consult going, my netbook has been sitting for over a year. Battery is screwed, have to get everything up and running on my laptop.