Let's talk about SC400 Ignition Coil Connectors
01-05-15, 01:35 PM
#16
Well the connectors came in today.
They didn't fix my problem.
Here's where I'm at now:
Newer caps/rotors, new coils, new plugs/wires. I'm going to guess it's not an ignition issue.
The engine idles at a constant RPM. There's a very slight vibration at idle. If I add throttle slowly, there's a more pronounced vibration. It seems to clear up in the higher RPM range. If I put the car in drive or reverse and lightly hold the brakes, the vibration is enough to make the car shake a little bit.
I'm at a loss. Can't imagine what else it could be. I can barely hear what sounds like an exhaust leak under the car right behind the front wheels. Even if that's what the sound is, I don't think an exhaust leak would cause shaking and vibration under acceleration, would it?
Would it be possible that in the 30ish miles of driving my car with no coil, that the cat crapped the bed and that's what's causing my issue now?
They didn't fix my problem.
Here's where I'm at now:
Newer caps/rotors, new coils, new plugs/wires. I'm going to guess it's not an ignition issue.
The engine idles at a constant RPM. There's a very slight vibration at idle. If I add throttle slowly, there's a more pronounced vibration. It seems to clear up in the higher RPM range. If I put the car in drive or reverse and lightly hold the brakes, the vibration is enough to make the car shake a little bit.
I'm at a loss. Can't imagine what else it could be. I can barely hear what sounds like an exhaust leak under the car right behind the front wheels. Even if that's what the sound is, I don't think an exhaust leak would cause shaking and vibration under acceleration, would it?
Would it be possible that in the 30ish miles of driving my car with no coil, that the cat crapped the bed and that's what's causing my issue now?
Last edited by MongooseGA; 01-05-15 at 01:43 PM.
01-05-15, 01:55 PM
#17
Broken record... I'd be shocked if it isn't your IAC Valve. Your symptoms match mine to a tee.
That's the part that finally convinced me to take a closer look a the IACV. When you're on the brakes, i.e. no throttle unless doing some crazy heel-and-toeing around town, it's the major component in passing air to the engine. I was more inclined to think it was a TPS issue before looking at it that way.
If I put the car in drive or reverse and lightly hold the brakes, the vibration is enough to make the car shake a little bit.
01-05-15, 01:57 PM
#18
Broken record... I'd be shocked if it isn't your IAC Valve. Your symptoms match mine to a tee.
That's the part that finally convinced me to take a closer look a the IACV. When you're on the brakes, i.e. no throttle unless doing some crazy heel-and-toeing around town, it's the major component in passing air to the engine. I was more inclined to think it was a TPS issue before looking at it that way.
That's the part that finally convinced me to take a closer look a the IACV. When you're on the brakes, i.e. no throttle unless doing some crazy heel-and-toeing around town, it's the major component in passing air to the engine. I was more inclined to think it was a TPS issue before looking at it that way.
01-05-15, 02:04 PM
#19
It's spread across multiple troubleshooting threads as I chased down various hunches...
My idle was very steady, aside from when it would get the shudders like you described. When the IACV becomes problematic, I think it's mostly a matter of being slow to respond, which fits my theory that cleaning/lubing or replacing the bearings is more significant that cleaning the shaft and tip. That bogged down feeling would seem to be a result of it not opening or closing quick enough to keep the engine happy with no or light throttle.
My idle was very steady, aside from when it would get the shudders like you described. When the IACV becomes problematic, I think it's mostly a matter of being slow to respond, which fits my theory that cleaning/lubing or replacing the bearings is more significant that cleaning the shaft and tip. That bogged down feeling would seem to be a result of it not opening or closing quick enough to keep the engine happy with no or light throttle.
01-05-15, 02:06 PM
#20
It's spread across multiple troubleshooting threads as I chased down various hunches...
My idle was very steady, aside from when it would get the shudders like you described. When the IACV becomes problematic, I think it's mostly a matter of being slow to respond, which fits my theory that cleaning/lubing or replacing the bearings is more significant that cleaning the shaft and tip. That bogged down feeling would seem to be a result of it not opening or closing quick enough to keep the engine happy with no or light throttle.
My idle was very steady, aside from when it would get the shudders like you described. When the IACV becomes problematic, I think it's mostly a matter of being slow to respond, which fits my theory that cleaning/lubing or replacing the bearings is more significant that cleaning the shaft and tip. That bogged down feeling would seem to be a result of it not opening or closing quick enough to keep the engine happy with no or light throttle.
I was able to spin the tires the other night with the same issue. It was perfect when I first got on the highway after swapping all of the plugs/wires, but within a little bit reverted back to the hesitation. Light throttle brought up shaking and vibration, heavy throttle seemed to power right through it.
01-05-15, 02:11 PM
#21
Yeah, it always smoothed out over 35-40 mph, or ~1400 RPM, depending on the amount of throttle. There was never any loss of power evident. Like you, I could usually push through it if I gave it more throttle up front, but even so, I could usually feel a bit of the grumbly hesitation. Then it would be fine for a few days and make me question my sanity.
01-05-15, 02:21 PM
#22
Yeah, it always smoothed out over 35-40 mph, or ~1400 RPM, depending on the amount of throttle. There was never any loss of power evident. Like you, I could usually push through it if I gave it more throttle up front, but even so, I could usually feel a bit of the grumbly hesitation. Then it would be fine for a few days and make me question my sanity.
What, if any, are the negative aspects of driving with a bad IACV? Fuel mileage loss? Any additonal build up? Additional heat being transferred anywhere? Is there a way I can test mine with a voltmeter maybe?
Last edited by MongooseGA; 01-05-15 at 02:24 PM.
01-05-15, 02:33 PM
#23
Did your car throw a CEL with the bad valve? FWIW, mine has no CEL showing.
What, if any, are the negative aspects of driving with a bad IACV? Fuel mileage loss? Any additonal build up? Additional heat being transferred anywhere? Is there a way I can test mine with a voltmeter maybe?
You can test it, but it's a pretty intricate test procedure and probably won't tell you anything... Here's the mini-guide I linked to in my IACV post mentioned earlier in the thread:
https://www.clublexus.com/forums/per...ml#post5781310
01-05-15, 02:52 PM
#24
Thanks for the info. I took some videos earlier of the car to show some of the symptoms.
First one is just me backing down my driveway about 30 feet or so. The shakiness in the video is caused by the very mild 'bucking' that happens when I hold the brakes and let the car move without throttle.
Second one is just a little bit of revving to give an idea of the sound I'm getting when adding throttle. It's very slight, and difficult to hear, but it's there in the lower RPMs and mostly goes away as the engine speeds up. Turn up your speaker (because the exhaust sounds pretty sweet, too
)
First one is just me backing down my driveway about 30 feet or so. The shakiness in the video is caused by the very mild 'bucking' that happens when I hold the brakes and let the car move without throttle.
Second one is just a little bit of revving to give an idea of the sound I'm getting when adding throttle. It's very slight, and difficult to hear, but it's there in the lower RPMs and mostly goes away as the engine speeds up. Turn up your speaker (because the exhaust sounds pretty sweet, too
)
01-07-15, 06:07 PM
#25
man that coil connector was super broken never really seen one that bad. surprised it didn't fix the issue to be honest. have you done the rotors in the distributors yet? if not thats probably the culprit. they start to act funny now and then as they get worse then they will just go out and sometimes on sc400's they sort of disintegrate. worth a check on the problem side at least. you can bet the other one will be just as good/bad.
http://farm9.staticflickr.com/8250/8...51501585_c.jpg
your idle rpm's look perfect for a mostly warmed up car. your iacv is likely working just fine I wouldn't take it apart to be honest after looking at the video. is the idle higher when its cold, likw 1100-1300? if it is then its doing what it should do I wouldn't mess with it.
I couldn't hear anything in the video, can you take another go at describing the problem.
almost sound like you might have just broken a motor mount or something.
http://farm9.staticflickr.com/8250/8...51501585_c.jpg
your idle rpm's look perfect for a mostly warmed up car. your iacv is likely working just fine I wouldn't take it apart to be honest after looking at the video. is the idle higher when its cold, likw 1100-1300? if it is then its doing what it should do I wouldn't mess with it.
I couldn't hear anything in the video, can you take another go at describing the problem.
almost sound like you might have just broken a motor mount or something.
01-07-15, 07:17 PM
#27
man that coil connector was super broken never really seen one that bad. surprised it didn't fix the issue to be honest. have you done the rotors in the distributors yet? if not thats probably the culprit. they start to act funny now and then as they get worse then they will just go out and sometimes on sc400's they sort of disintegrate. worth a check on the problem side at least. you can bet the other one will be just as good/bad.
http://farm9.staticflickr.com/8250/8...51501585_c.jpg
your idle rpm's look perfect for a mostly warmed up car. your iacv is likely working just fine I wouldn't take it apart to be honest after looking at the video. is the idle higher when its cold, likw 1100-1300? if it is then its doing what it should do I wouldn't mess with it.
I couldn't hear anything in the video, can you take another go at describing the problem.
almost sound like you might have just broken a motor mount or something.
http://farm9.staticflickr.com/8250/8...51501585_c.jpg
your idle rpm's look perfect for a mostly warmed up car. your iacv is likely working just fine I wouldn't take it apart to be honest after looking at the video. is the idle higher when its cold, likw 1100-1300? if it is then its doing what it should do I wouldn't mess with it.
I couldn't hear anything in the video, can you take another go at describing the problem.
almost sound like you might have just broken a motor mount or something.
I could see the motor mount idea, but the way the rough feeling came in then went out, came in then went out pretty much rules that out for me. It's gotta be something electric or a moving part of some kind.
Wager the cost of the repair for the car for me.
01-08-15, 08:05 AM
#28
just mentioning the mount cause I have seen a few sc400 with broken motor mounts. people think its rough idle issues but if you think about a motor thats balancing on 3 points and then you take one of them away its going to move around and vibrate especially idle right off idle. when you step on it you won't notice it until the other one breaks, and that would be bad. I am not sure if there is a quick test or not, if I think of anything else I will let you know. I know 99sc42 has replaced them several times maybe he might be able to give more of an idea of what its like.
Your car has pretty low miles and with the big exhaust it seems to sound good in the video. sounds a touch rich at times but thats exactly what i would expect from that modification.
Your car has pretty low miles and with the big exhaust it seems to sound good in the video. sounds a touch rich at times but thats exactly what i would expect from that modification.
01-08-15, 07:21 PM
#29
just mentioning the mount cause I have seen a few sc400 with broken motor mounts. people think its rough idle issues but if you think about a motor thats balancing on 3 points and then you take one of them away its going to move around and vibrate especially idle right off idle. when you step on it you won't notice it until the other one breaks, and that would be bad. I am not sure if there is a quick test or not, if I think of anything else I will let you know. I know 99sc42 has replaced them several times maybe he might be able to give more of an idea of what its like.
Your car has pretty low miles and with the big exhaust it seems to sound good in the video. sounds a touch rich at times but thats exactly what i would expect from that modification.
Your car has pretty low miles and with the big exhaust it seems to sound good in the video. sounds a touch rich at times but thats exactly what i would expect from that modification.
A buddy of mine also thinks there's a fuel issue. Could be either bad gas (which I've had before and I remember the can ran rough for a through the whole tank) or a fuel pressure issue. I just did the 12V fuel mod a few thousand miles ago, I'd be very surprised if it caused the pump to go bad already. Plus, the fact that the problem went away and came back...
I'll check out an IACV; they're cheap and easy to swap. Buddy wants to put a fuel pressure gauge on the car to test that theory as well. I'll also go a head and put in the new fuel filter I've had in my garage for a few months...
01-08-15, 08:28 PM
#30
The only thing that sucks about changing the IAC Valve on yours is you have to drain the coolant, since the whole assembly has to come off, not just the valve like with the serviceable ones.