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Why does my Intake Air Control Valve keep on failing?
After swapping a JDM SR20 into my 99 sentra se I have started experiencing idle problems. All of them seem to be related to a bad IACV (or IAVC?).
The first IACV (entire unit including the idle screw) was swapped from my original motor and installed on the JDM. It was working fine until my idle started going really low. I tried to adjust the idle with the idle screw located on the IACV but turning it did not do anything.
The second IACV (entire unit including the idle screw) came from a 93 sentra and it worked fine for about 3 months. I experienced a similar issue where my idle started going really low. Once again I started adjusting the idle with the idle screw located on the IACV but this time the screw will not budge
I'm about to order a brand new IACV - but before I do and install it (PIA on the highports) - I was wondering if there could be anything causing the IACV to fail, or do I simply have bad luck with this.
Thanks in advance,
PK
Last edited by akapaul; 12-29-2004 at 02:24 PM.
Reason: spelling
No, EGR has not been swapped yet. I will have to do that though if I want to pass emissions. Would EGR have an influence on this? It seems to be a mechanical problem with the IACV, because why would the screw get 'stuck' and not turn left or right?
Someone advised me to get one of those impact screwdrivers and see if I can bust the screw loose, but I'm nervous to break it even more. I can't have downtime with my car if this happens.
I tightened the throttle cable for now to keep my idle up
There are two valves, one brings in air for idle when the TB is closed and one is for idle adjust. You are having issues with the idle one and it is not the one with the idle screw on it. It is the AIV that sits under the IM, not on the end of the IM that brings in idle air. Take a look at that. Make sure it is hooked up!
Brent
__________________ Coach - EEN Member/The Fist Don't F with me!
1993 NX 2000 -- Slate Grey Metallic
1999 SE-L -- back to NA form
Is the IAVC the same as the AAC valve? I think that's one of the problems with my idle right now on my JDM SR20 swap. We still have more troubleshooting to do.
Thanks,
Todd
__________________
-06 EVO IX RS
-93 SE-R (prepping to sell in the Spring)
-69 Camaro SS (project car)
THose would be different, and it is that AAC i and not AIV that i was reffering above. I get them all mixed up! To many letters! Anyway, explanation still fits. Look for the under the IM I hear the JDM valve allows to little(?) air in and stalls the car out when using a JWT or USDM ecu.
It's confusing as all hell, it really is. The unit that Paul is referring to is the IAA Idle Air Adjusting unit. This assembly includes the IAS (Idle Adjusting Screw), FICD (Fast Idle Control Device) and the IACV-AAC (Idle Air Control Valve Auxillary Air Control Valve). The FICD raises idle when engine loads like the alternator, or A/C compressor are encountered, to keep the idle the same as when those loads are less prevelent. The IACV-AAC operates on a pulse signal from the ECU and allows an air bypass of some sort. Now the IACV Air Regulator is another device entirely, the one brent mentioned, which is under the intake manifold, and is an air bypass that makes the engine idle faster when it's cold so that the engine warms up quickly. There's a bimetal that operates a shutter which closes as the bimetal warps. The bimetal is heated up by current that passes through it constantly, the entire time the engine is running. This shutter has an adjustment nut that allows you adjust the full open/closed positions. It should be fully closed when it's hot and open when it's cold.
I've dealt with all these things at length to address my nosediving idle that occurs when the engine is cold, and the outside temperatures are cold. It only nosedives when the engine has been under load and then put into neutral. It drops way down, jumps up, goes back down and then usually levels back off. I've cleaned the sh*t out of the IAA and I've swapped the Air regulator and adjusted the shutter. Other than the ECU, I'm not sure what's causing my problems. I also have that nifty stumbling acceleration but that seems to occur less when the engine is cold and the air is cold, then it's not there and the car pulls like there's no tomorrow. Frankly, I'm tired of this sh*t and I'm tired that nobody has a straight answer, and by god, if I figure out what's causing it, it's going to be a goddamn sticky and I'm going to nominate myself for forum member of the decade.
Rob, hows the EGR (oh no, not another acronym!!). Is there a way to verify the operation of all the idle control devices? The FSM is really helpful in figuring out what all the idle stuff does. Its all in the beginning of the main section in there.
It's confusing as all hell, it really is. The unit that Paul is referring to is the IAA Idle Air Adjusting unit. This assembly includes the IAS (Idle Adjusting Screw), FICD (Fast Idle Control Device) and the IACV-AAC (Idle Air Control Valve Auxillary Air Control Valve). The FICD raises idle when engine loads like the alternator, or A/C compressor are encountered, to keep the idle the same as when those loads are less prevelent. The IACV-AAC operates on a pulse signal from the ECU and allows an air bypass of some sort. Now the IACV Air Regulator is another device entirely, the one brent mentioned, which is under the intake manifold, and is an air bypass that makes the engine idle faster when it's cold so that the engine warms up quickly. There's a bimetal that operates a shutter which closes as the bimetal warps. The bimetal is heated up by current that passes through it constantly, the entire time the engine is running. This shutter has an adjustment nut that allows you adjust the full open/closed positions. It should be fully closed when it's hot and open when it's cold.
I've dealt with all these things at length to address my nosediving idle that occurs when the engine is cold, and the outside temperatures are cold. It only nosedives when the engine has been under load and then put into neutral. It drops way down, jumps up, goes back down and then usually levels back off. I've cleaned the sh*t out of the IAA and I've swapped the Air regulator and adjusted the shutter. Other than the ECU, I'm not sure what's causing my problems. I also have that nifty stumbling acceleration but that seems to occur less when the engine is cold and the air is cold, then it's not there and the car pulls like there's no tomorrow. Frankly, I'm tired of this sh*t and I'm tired that nobody has a straight answer, and by god, if I figure out what's causing it, it's going to be a goddamn sticky and I'm going to nominate myself for forum member of the decade.
have you watched the tps values under deceleration? my car does that, my girlfriends ga16 does it, about 12-15 customer cars that i have worked on do that also (all 90's nissans ranging from the ka24de to the sr to the ga16)
haven't figured out anything yet. of course i haven't put my scanner on it, it seems that after 9-10 hrs of wrenching on other peoples cars i haven't the time or passion to fix my own.
Allright then. I am not the only one out there with these issues. I keep pointing towards my TPS as well, but don't really have a good understanding of how to test it. Every time I check the readings on it they are within the specs.
I already cleaned out my IAA and surroundings extensively and I bypassed the EGR (nippled off) to see if that helped. Nope!
Someone hopefully will find a result.
__________________
Brandon
'02 Maxima SE 6MT
'96 G20 (SOLD)
I replaced my IAA with a brand new dealership part and I still have the same issues I had before. Other than cleaning my TB and totally removing the EGR I don't know what else to do. I've checked my TPS and it's within spec, but that's not to say that it doesn't have a sh*tty spot right around 2500 RPM. It could very well be that that is a common RPM point for this car and the contacts in the TPS at that point could be an issue. I think I've even swapped my TPS for another with no change. I could check my TPS values under deceleration like Creagach mentioned. I also should make sure my MAF wire looks ok. I've got a spare MAF and ECU I could plug in to see if anything changes.
Last edited by Toolapcfan; 04-21-2005 at 05:40 PM.
I replaced my IAA with a brand new dealership part and I still have the same issues I had before. Other than cleaning my TB and totally removing the EGR I don't know what else to do. I've checked my TPS and it's within spec, but that's not to say that it doesn't have a sh*tty spot right around 2500 RPM. It could very well be that that is a common RPM point for this car and the contacts in the TPS at that point could be an issue. I think I've even swapped my TPS for another with no change. I could check my TPS values under deceleration like Creagach mentioned. I also should make sure my MAF wire looks ok. I've got a spare MAF and ECU I could plug in to see if anything changes.
My 93 SE-R does excatly the same thing you were describing with the idle jumping when shifted out of gear and into neutral while driving. As far as mine car goes, the EGR had nothing to do with the idle jumping, does the same thing before and after it was off. My 93 also has a rough patch at around the rpm on occasion. I am pretty sure that the MAF just needs to be regrounded.
I replaced my IAA with a brand new dealership part and I still have the same issues I had before. Other than cleaning my TB and totally removing the EGR I don't know what else to do. I've checked my TPS and it's within spec, but that's not to say that it doesn't have a sh*tty spot right around 2500 RPM. It could very well be that that is a common RPM point for this car and the contacts in the TPS at that point could be an issue. I think I've even swapped my TPS for another with no change. I could check my TPS values under deceleration like Creagach mentioned. I also should make sure my MAF wire looks ok. I've got a spare MAF and ECU I could plug in to see if anything changes.
Rob, lets take it from the top... again.
What is the exact problems that you have now?
Fromt the descriptions you gave above I assume that:
CAR STATUS
1. New IAA Unit (that means new AAC, new FICD, new IAA screw).
2. EGR on car.
3. Idle Air Regulator clean and adjusted.
4. TB that possible needs cleaning.
5. TPS within specs under deceleration (what exactly did you monitor ?) but with a sh*tty (like ?) point @ 2500rpm
6. I assume that timing is also a t some reasonable range (13-17 deg) and that the O2 sensor is good and checked.
TROUBLE CONDITION 1
Engine temp LOW (how low? where does the symptom dissapear temp wise?) +
Ambient temerature LOW
+
Car was under load AND changed to Neutral AND gass OFF
THEN
Idle nosedives and oscilates a bit before settling.
TROUBLE CONDITION 2
When Engine temp OK and Ambient Temp Medium
THEN
Stumbling Acceleration
(how does it "stumble" ? what rpm? how long? Once or repeatedly?)
When Engine Cold + Ambient Low this one does NOT appear.
Right? Anyhting else or a [?} you might add/describe?
Rob, lets take it from the top... again.
What is the exact problems that you have now?
CAR STATUS
1. New IAA Unit (that means new AAC, new FICD, new IAA screw).
2. EGR on car but disabled.
3. Idle Air Regulator clean and adjusted.
4. TB that possible needs cleaning.
5. TPS within specs checked readings per FSM
6. Not sure about timing since "timing mode" exists in the realm of the Easter Bunny and Santa Claus. I've never been sure if I've gotten it into the mythical "timing mode" but I believe it's set at 17*. These conditions existed before I ever adjusted timing as well.
7. New O2 sensor.
8. MAFS readings within specs per FSM and reground.
9. Checked for intake air leak per FSM and checked out OK.
10. New NGK plugs, NGK wires, new cap and rotor.
11. Performed power balance check per FSM and checked out OK.
12. I've never checked compression or fuel pressure
13. New fuel pump, gas cap and fuel filter.
TROUBLE CONDITION 1
Engine temp doesn't appear to make a difference
+
Ambient temerature LOW
+
Car was under load AND changed to Neutral AND gass OFF
THEN
Idle nosedives and oscilates a bit before settling.
TROUBLE CONDITION 2
When Engine temp warm
+
Ambient temp doesn't seem to have an effect
+
Stumbling Acceleration around 2500-3000 RPM, not extreme like an ignition miss though
When the engine is still cool this doesn't seem to happen at all or is less noticeable.
Here is something I ran into while doing my phenolic spacer install 2 years ago. After putting on the TB spacer it changed my TPS valves and I had to adjust my throttle cable to compensate. However when I did that it threw off the IDLE SWITCH setting completely. But I do have a tectom mdm-100 so it took nearly 2 hours of playing with the TPS to get the IDLE SWITCH ON at idle while getting the 0.45-0.55v for idle. The main thing is you have to get the car into timing mode before setting the idle.
All you do is have the engine fully warmed up then start it again with the TPS unplugged. Hold the engine at 2000rpm or so for a few seconds then rev the engine from 2500-3600rpm 3 times. That will lock in timing mode so the mark on the crank pulley won't be moving all over the place. After setting the ignition timing, then you adjust the idle. In my car the first line under the 1000rpm mark on the tach is about 800rpm, so to set the idle target for 700rpm I had to put the pointer between the 1st and 2nd marks under the 1k mark. After that turn the engine and plug in the TPS, so everything should be good to go.
Quote:
Originally Posted by Toolapcfan
CAR STATUS
1. New IAA Unit (that means new AAC, new FICD, new IAA screw).
2. EGR on car but disabled.
3. Idle Air Regulator clean and adjusted.
4. TB that possible needs cleaning.
5. TPS within specs checked readings per FSM
6. Not sure about timing since "timing mode" exists in the realm of the Easter Bunny and Santa Claus. I've never been sure if I've gotten it into the mythical "timing mode" but I believe it's set at 17*. These conditions existed before I ever adjusted timing as well.
7. New O2 sensor.
8. MAFS readings within specs per FSM and reground.
9. Checked for intake air leak per FSM and checked out OK.
10. New NGK plugs, NGK wires, new cap and rotor.
11. Performed power balance check per FSM and checked out OK.
12. I've never checked compression or fuel pressure
13. New fuel pump, gas cap and fuel filter.
__________________
91 Nissan Sentra SE-R: KYB AGX's, eibachs, prothane mounts, ES suspension bushings, addco RSB, FSTB/RSTB, CAI, JWT C2/ECU, 3in B-pipe, UR UDP, nitrous
Best ET: 13.57 @ 99mph
OK, since almost everything in there IS new, and you did everything that is suggested by the FSM in problem solving, we can assume that either of the following two situations (or both) exist:
1. There is a probelm in the connections somewhere from the sensor(s) to the ECU that makes a new and within specs sensor give bad readings to the ECU.
2. As posted by NISMO87SE, some interaction between componenet makes the whole thing go out of whack. You cannot see the exact out-of-whack situation but only the mysterious end result.
The only way I can see to go about resolving this, sort of a full scan with an oscilloscope, is to try and check the most suspect components in operation. A Techtom, DIY Consult with software, or whatever would be great. THe DIY option is even better since you can graph them over time.
AAC valve ON is shown by those thingies so if there is a IARV-IACV/AAC thing you will probably see it in the AAC duty cycle.
Form your description though, we can target confditons that lead to surging/unstable idle and "stumbling when engine is hot".
For the 2nd one, the only thing I did not see you mention is the check of the Active Carbon Canister "operation". Did you do that?
If I had to take a wild guess though, I would say that your problem is.... O2 sensor!!! The sensor might be great but the readings ther ECU gets may be wrong. The O2 sensor is the only sensor that appears in the FSM as a main culprit in all error-checking procedures relating to your symptoms. All of them! I would check it, first with the engien off and then with engine running. Maybe a bad ground or something makes it send a signal to the ECU that is "offset" be the ammount of the bad ground... you never know but let's tackle the problem.
Do you have access to a DIY COnsult or similar item?
I would have to resort back to a couple well know issues. EGR and idle setting.
I think the EGR is the main culprit for engine that stumble between 2500-3000 rpms.
I fought my idle for years, my car would die or the idle would drop once and then bounce around and recover. I finally fixed my idle by buying a Conzult interface for the ECU. It allows you to set the ECU into timing mode and adjust the TPS, Timing, and idle screw accordingly. After about 5 years of fighting the idle problem, it is finally fixed on my car, as well as a few friends that had the same problem.
6. Not sure about timing since "timing mode" exists in the realm of the Easter Bunny and Santa Claus.
LMAO. Sorry...I just found this amusing. I guess I'm just trying to lighten up this thread since I'm having some of the same idle problems which cause my SE-R to rot in the driveway instead of being the daily driver it was destined to be.
Goneturbo, I will buy you dinner if you can help me fix my idle problem. It is driving me nuts. Now with my S4 cams, it won't idle at all! Email me at gupamf@yahoo.com
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of course i haven't put my scanner on it, it seems that after 9-10 hrs of wrenching on other peoples cars i haven't the time or passion to fix my own. 
