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IACV and skipping / bucking question

 
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Old 01-22-2011, 11:24 PM
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IACV and skipping / bucking question

Two questions:

When shifting redline from a stop, 1st, 2nd and 3rd, between gears the front of the lude shakes real rough, like the front is bouncing. I've seen it before in other ludes. Is this because the amount of torque is so far greater then the weight, even more so past burning tires? Or that its not enough weight and the tires are skipping? Or how about I have bad mounts? lol

And second, about my rough idle. When it was bouncing I went and unplugged the IACV and it stopped, returning to normal rpm's. When I plugged it back it in pulsed real quick and the CEL came on. The fact that the fluctuating stopped with it unplugged, does that say anything? Is the valve bad? Or what does the car exactly do when its unplugged? So I can isolate where the problem might be.

It IS clean, cleaned it a couple days ago till only clear cleaning fluid was coming out of it.
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Old 01-24-2011, 10:24 AM
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Re: IACV and skipping / bucking question

For those who were following me with this, the idle is fixed.

It turned out to be a bad / dirty PCV valve, which sit just on top of your valve cover.

For people who are getting a slight rough idle, only when warm, and only when it wants to, check this. When the car has a fluctuating idle at a stop, get out and clamp the vacume hose from the intake manfi to the PCV on the valve, if the idle returns to normal then get a new valve. 3 bucks at a part store.
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Old 01-24-2011, 11:50 AM
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Re: IACV and skipping / bucking question

Negative, it's not the PCV valve, though it was dirty and needed to be replaced.

The list is getting slim now lol, down to 2 options.

I noticed the idle will only surge when the coolant fan is running, you can rev it as much as you want when its not running and it be fine. The second the fan turns on and you rev it the idle will bounce. It's odd that closing a vacuum line will stop it from bouncing, I'm thinking the mess-up is so slight that any difference in the system once its bouncing will auto-correct itself.

So the thermostat is the next thing to replace. Other then that, and god help me if it is, it could be electrical. Possibly turning the coolant fan on is drawing enough power from either the MAP, TPS or IACV sensors, and causing them to read wrong, resulting in the fluctuation. Though you'd think the radio, speakers..etc would cause the same problem, not to mention the alternator is only a couple months old. But after the thermostat that will be our next route to check.

I'll keep ya updated.
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Old 01-24-2011, 12:08 PM
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Re: IACV and skipping / bucking question

Or could be the coolant temperature sensors.

Dude, could be fuel related as well (fuel filter, lines, injector clogging, pump). Have to check fuel pressure as well. Also there is engine compression and timing to check.
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Old 01-24-2011, 12:11 PM
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Re: IACV and skipping / bucking question

Bad timing would cause the idle to bounce all the time, along with compression.

The MAIN thing in all this was first, I thought it would just do it when it wanted to, I could drive the car 100 miles and not have it happen once. I just discovered that it'll bounce with the thermostat open, only while the fan is on.

What coolant sensors are there?
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Old 01-24-2011, 02:11 PM
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Re: IACV and skipping / bucking question

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Originally Posted by Terror View Post
Bad timing would cause the idle to bounce all the time, along with compression.

The MAIN thing in all this was first, I thought it would just do it when it wanted to, I could drive the car 100 miles and not have it happen once. I just discovered that it'll bounce with the thermostat open, only while the fan is on.

What coolant sensors are there?
There is one coolant temp. sensor, with the green plug right next to the the thermostat. When you change your thermostat, you'll see it. It looks like new chalk end. It's different from the one that gives you the bars in the dash and different from the one that sets off the fan.

But, yeah, you have the ECU which is changing timing and fuel ratio all the time compensating for this and that all the time.
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Old 01-24-2011, 02:28 PM
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Re: IACV and skipping / bucking question

I'll check the sensor if the thermostat doesn't work.

But then it's an ECU problem at that point, cause if your timing is off your car is going to run like ****, all the time, it wouldn't make sense for the timing to be off, it run completely fine and only hickup the idle with the thermostat open. I'm no expect, but it seems like a very big longshot, though still may be possible. The timing belt was changed months ago, and this is a recent problem.

Fuel, eh, fuel is fuel lol. Not something I would think of, but it'll go onto the list if I exhaust all my other sources. The filters were changed, and if the pump goes out it goes out, doesnt really die out.

My father's a retired mechanic, so between him, the internet, and trial and error we'll figure it out.

I appreciate the feeback though.
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Old 01-24-2011, 02:44 PM
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Re: IACV and skipping / bucking question

Quote:
Originally Posted by Terror View Post
I'll check the sensor if the thermostat doesn't work.

But then it's an ECU problem at that point, cause if your timing is off your car is going to run like ****, all the time, it wouldn't make sense for the timing to be off, it run completely fine and only hickup the idle with the thermostat open. I'm no expect, but it seems like a very big longshot, though still may be possible. The timing belt was changed months ago, and this is a recent problem.

Fuel, eh, fuel is fuel lol. Not something I would think of, but it'll go onto the list if I exhaust all my other sources. The filters were changed, and if the pump goes out it goes out, doesnt really die out.

My father's a retired mechanic, so between him, the internet, and trial and error we'll figure it out.

I appreciate the feeback though.
What I'm saying is that when the coolant temperature reaches a certain point, maybe the ECU goes into a different algorithm than when it's cold. Like it throws in different fuel ratios or changes the timings differently than when the engine is cold. Yeah, it's a longshot possibility. Try to get the ECU to work on open loop if you can by unhooking the sensors to see if a sensor is the culprit. I know you can unhook the coolant temperature sensor and the O2 sensors.

Anyway, good luck with it. Yeah, I'm no trained mechanic so I'm making guesses here, LOL. Take it with lbs of NaCl.
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Old 01-25-2011, 05:41 PM
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Re: IACV and skipping / bucking question

I replaced the thermostat and the car seems different. Either a lot more torque or its bucking shifting gears, can't seem to get it smooth. But the idle is still ****ed up. It will only happen when driving and will only bounce a couple times and stop. Not enough time to get out and under the hood.

Does this sound like a coolant bubble? Even since I've had the car when your driving and push the clutch in and let it drop, it'll go to 700 rpm up to 1100 then rest at 900. Slow too.

Any thoughts?

Last edited by Terror; 01-25-2011 at 06:12 PM.
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Old 01-26-2011, 12:17 PM
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Re: IACV and skipping / bucking question

Current status;

All the previous times I would clamp down the PCV valve line and the bouncing would stop, though the thought was the change in air is fixing whatever the problem is, not that the line was the problem itself, for the valve is brand new.

I caught it today and tried clamping down other lines, of which none of them eased the idle. Only the PCV. I noticed it was sitting wrong in its seal, so it's been reseated firmly.

Waiting on the results next time I drive it around.
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Old 01-26-2011, 04:21 PM
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Re: IACV and skipping / bucking question

it kinda sounds like you and I have the same problem read my thread just above yours called irritating idle. mine revs up and downwhen warm at stops and I've checked alot pcv, iacv, fitv, one thing I haven't checked iss the coolant sensor and don't know how to check the thermostat but I was thinking ity might be the thermostat
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Old 04-24-2011, 07:18 PM
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Re: IACV and skipping / bucking question

The ECU shifts modes when the thermostat opens, its called closed loop, or maybe its called open loop. I cant remember which that always confuses me.
Anyway, when the temperature gets up to a certain point the thermostat opens, which sends the signal to the ECU to start using all the sensors. This is why they say to troubleshoot the car needs to be warm!
I'm having the same issue with my car at the moment and heres what I've done so far.

Replaced IACV
Replaced vacuum lines
Replaced spark plugs
Replaced head gasket (yes, I went that far, this is so annoying I thought I was injecting gasses into my coolant causing my IACV to fluctuate)
Replaced timing belt and water pump
Adjusted dizzy timing (the previous owner had it maxxed out to full advanced the idiot)
Cleaned FITV and tightened the white plastic insert

Now I'm going to replace my PCV today AGAIN, and the line that it runs on. As well as make sure that thing is firmly mounted in there.
If this doesnt work I'm going to remove the Intake Manifold and thoroughly clean it all out, along with the throttle body, and replace all the gaskets involved in said project.
I'll let you guys know when I get that little ordeal finished and let ya know if it works.
(I might want to know if your coolant sensor swap fixes it so let me know!

My surge is so bad it goes from 600 up to 2000, up and down up and down. SO annoying.
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Old 04-25-2011, 05:54 PM
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Re: IACV and skipping / bucking question

I seem to have this problem as well, its becoming very jumpy. I tried to locate the fitv but could not. I have already cleaned the IACV, I just need to clean the EGR valve and the FITV. Is there any way I could locate these and clean them without removing too many components in the engine? I have a 5th gen with a h22a4. Much help would be appreciated!
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Old 04-27-2011, 12:55 AM
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Re: IACV and skipping / bucking question

have any of you bled your coolant? I've heard that it could lead to a fluctuating idle...

oh btw I have this same problem...sometimes
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