Idle dropping/stalling when coasting...

[sirgilbert357]

Here's my issue: when coasting in neutral at any speed, the idle drops to the very lowest hash mark it can go without dying (500 RPM's??). If I have my headlights on or I hit the brakes hard enough (or both), I can kill the car. After coming to a complete stop, the car takes about 10 seconds to slowly idle back up to 700 where it should be (even if the headlights are still on and I'm hitting the brakes). Then, its fine.OK, I have searched and searched and I found this:

zerothread?id=254278

I did everything except the last one: clean the IACV. But I did take the hose off and spray a bunch of carb cleaner in there while revving the engine (no, it didn't smoke like crazy like some say though). No difference at all. The only mods are an AEM intake and Brian Crower stage 2 cams and I have the AIV box unhooked from the intake, but still installed. So, I have replaced the MAF, the distributor rotor and cap, new wires, new O2 sensor (the first one in the header), new fuel filter, semi new injectors (guy that sold me the car 6 months ago had them installed about 8 - 10k miles ago, but I have had this issue the whole time I've owned the car) and still no change in how the car drives. I also cleaned the throttle plate when installing the intake just cause I was there and there was no gunk or build up. It doesn't hesitate on WOT at all and idles fine after sitting at a light for about 10 seconds, so WTF?

Could it be the exhaust gas temp sensor? (Some people are telling me my car has this, others say only the California ones have it?)Coolant temp sensor (I don't know why this would cause the issue or where it is even located)The second O2 sensor in the header? (By the way, would that be the same part # as the first one I've already replaced?)TPS? (I personally doubt it because the throttle works fine all other times)IACV? (I was told the duty cycle of this part is only on warm up and should not affect the car at all after its at normal operating temp).Bad throttle body assembly (Loose spring, cable or something? It snaps back fine when actuating it manually and there isnt too much play in the cable...)

I have checked and re-checked all vacuum hoses and even replaced every hose that has to do with the intake. I made my own grounding kit (the car is grounded in 4 different places in the engine bay) as well. Should I totally disconnect the throttle body and degrease it completely with carb cleaner or something?

I am at my wits end with this crap and I have looked at taking the EGR off, but don't want to if thats not the issue...I cant get to the IACV because I don't have baby hands and the EGR is partially in the way, and why pay a shop to remove and replace the IACV if thats not the issue? Someone help me here... Please.

[Rucca]

This may or may not be your problem but you need to clean the IACV properly, spraying carb cleaner in it's hose won't fix it. Clamp off the air line to the IACV while the car is idling and see if you notice a change. If your problem improves then shove your fat hands back there and take it off, it isn't in the best spot, but definitely accessible.

Have you tested your alternator? They do it for free at Autozone.

Check for vacuum leaks, also if you have a vacuum gauge ($2.50 at Harbor Freight) I would check your vacuum readings at idle, part throttle, and snap throttle.

Instead of removing the EGR, check to see if it is stuck open. Actuate the diaphragm by hand while the car is idling and see if it stalls or bogs.

I'd also plug the PAIR system on the exhaust end - doubt this is your problem but you may be leaking CO into the engine bay and thus into your cabin.

EGT - No even if you had oneCTS - I think this would cause more of a high idle problem, but it is easy to replace and under $20. It is a red plug on your coolant inlet sort of near the throttle body. Just unscrews.Second O2 - No, would set a code for emissionsTPS - Doubt it. If you unplug it the idle will raise significantly but your problem will probably still happen.IACV - Yes, if it isn't allowing enough air to bypass the throttle body.TB Assembly - No - you wouldn't have other problems, like revs not dropping.

[sirgilbert357]

This may or may not be your problem but you need to clean the IACV properly, spraying carb cleaner in it's hose won't fix it. Clamp off the air line to the IACV while the car is idling and see if you notice a change. If your problem improves then shove your fat hands back there and take it off, it isn't in the best spot, but definitely accessible.

Have you tested your alternator? They do it for free at Autozone.

Check for vacuum leaks, also if you have a vacuum gauge ($2.50 at Harbor Freight) I would check your vacuum readings at idle, part throttle, and snap throttle.

Instead of removing the EGR, check to see if it is stuck open. Actuate the diaphragm by hand while the car is idling and see if it stalls or bogs.

I'd also plug the PAIR system on the exhaust end - doubt this is your problem but you may be leaking CO into the engine bay and thus into your cabin.

EGT - No even if you had oneCTS - I think this would cause more of a high idle problem, but it is easy to replace and under $20. It is a red plug on your coolant inlet sort of near the throttle body. Just unscrews.Second O2 - No, would set a code for emissionsTPS - Doubt it. If you unplug it the idle will raise significantly but your problem will probably still happen.IACV - Yes, if it isn't allowing enough air to bypass the throttle body.TB Assembly - No - you wouldn't have other problems, like revs not dropping.

Thanks for the reply... Yeah, tested alternator and its good.If I do the pinching of the vacuum line thing while its running, what should happen if its a bad IACV...cause it runs fine while just sitting there...its only when the car is in motion and in neutral.No vacuum leaks, have checked those...When actuating the EGR by hand, if it DOES stall, does that mean it is good? What should happen if it is bad?Thanks for all the help, I really appreciate it...

[Rucca]

Actuating the EGR by hand at idle should stall or severely bog your car down. For a further test, try removing and plugging the vacuum line to the EGR diaphragm and drive it around. If problem solved, then you know it is EGR related.

The IAC line pinching should also drop idle down.

Do you have the factory service manual downloaded? It is a great resource and can really help diagnose issues like this.

[sirgilbert357]

OK, I will try unhooking that vacuum line to the EGR. So, I should still be able to drive it around like that without it stalling out? And with the IACV, if I pinch that line off and there is no drop in idle, this indicates that its gone bad? Is it possible that it is just really slow to respond and thats why its taking about 10 seconds for the car to return to a normal idle after coming up to a light? Funny thing is, if I coast for a full minute, the idle will be near dying for a min, if I coast for only 10 seconds, it will only near die for 10 seconds. So is the ECU getting input from some sensor that the car is still rolling? Because it only happens while the car is rolling, so its starting to make me think its not just a problem with these two parts, but some incorrect input from a sensor...

And no, I dont have the manual. I will download it, do you have a link where I could get it?

[aarsey136]

Is your service engine light on? If it is check your codes. That will remove guess work.Even if light isnt on check them anyway , light may not work. This problem will throw a code. You can check codes yourself. Fairly simple and the only cost is the computer code book bought at any parts house.

[Rucca]

Is this an automatic transmission?

[sirgilbert357]

Is this an automatic transmission?

Nope, its a 5 spd. And no check engine light, but yeah, i need to pull the codes in case the bulb just isn't working. I have an OBD II reader and the code book, but I understand the codes are different with the 240. I have those too, there is a write up on here about what to check for each code...but I was hoping someone could chime in without the codes...

[sirgilbert357]

This is what i have for the codes. If this is not right and the codes are standard OBD I and II codes, then I have those too. My car is a 93, so can someone clarify which codes I will encounter?

TROUBLE SHOOTING (1991 240sx)******************HIGH IDLE: 5,8,13,21UNSTABLE IDLE:after warm-up:-10,25,2,4,7,1,13,8,3,12,17,18hunting:-13,25,7,8,10ENGINE STALL:Cold-9,25,2,4,7,1,17,19,18Hot-15,25,,2,4,1,17,19,18,20On momentary acceleration-9,25,2,4,1,17,19,18after deceleration-9,3,25,2,4,1,13,17,19,18acceleration or cruising-25,2,4,1,8,17,19,18heavy electrical load-6,25,2,4,1,17,19,18While turning-25,2,4,1,17,19,18

Symptom definitions:===============1.ensure fuel pressure within spec2.perform appropriate test in injector malfunction diagnostic chart3.inspect throttle body ports and valves for deposits, wear or plugging4.check for spark using spark tester5.Check idle speed control circuit.6.Ensure battery is fully charged and maintains at least 9.6 volts during cranking.7.check spark plug gap and fouling8. ensure no vacuum leaks in intake system9.Check fast idle system.10.check egr control valve operation11.Check EGR control valve solenoid operaton.12. check engine compression13. disconnect exhaust gas sensor and monitor change in driveability. if it improves, replace sensor. if not, go to 16.14.Remove canister purge line from intake and test drive vehicle.15.Remove vacuum hose from fuel pressure regulator and monitor for symptom change.16.enter self-diagnosis mode 11 and monitor exhaust gas sensor operation17.check ecu harness connector18.try a good known ecu19.Check ECU power source and ground circuit.20.Check timing belt for proper installation(V6 models)21.Check throttle linkage operation.22.Try a known good airflow meter.23.Check for intake valve deposits.24.Check engine temperature sensor25.perform power balance test

With most of these codes there is a lot of crap I would be doing. A lot of people I have talked to think it is my IACV, so I just want a few more opinions before getting under the car and fighting the war I know I have coming if I have to take the IACV off myself (dealer wants 135 just to install a new one!!)...

[vancouverbc]

those are not codes. just trouble shooting guide which isnt very helpful. the iacv isnt that hard to get off. just takes time to figure out how to do it. i assume the $135 is just the labour part. you can buy a new iacv for around $100.