rough cold idle

No your computer has learned that it has to have the idle air control valve open to idle. Now that you have enough air getting by your tb, reset the computer and let it relearn. The IAC will close when it sees the idle is to high
 
Whoa -whoa-whoa guys!!!! DONT GET HIM ADJUSTING THE TB BLADES as you will throw of the TPS sensors determined idle! THE IAC IS SUPPOSED TO LET THE ENGINE BREATH AT IDLE AND WILL SUCK A LOT OF AIR!! AND IF YOU PINCH IT OFF, OF COURSE IT WILL KILL THE ENGINE! IT'S JOB IS TO FEED THE ENGINE AIR WHEN YOU LET OFF THE THROTTLE AND AT IDLE, BECAUSE YOUR THROTTLE BLADE IS CLOSED CHOKING THE ENGINE. THE IDLE AIR CONTROL VALVE LET'S THE AIR IN TO KEEP THE ENGINE IDLING AND HAPPY!

I do think it could be a faulty IAC though. You also should look at all wiring because the MAP could do the same type thing with the idle. It could be measuring false readings in the manifold and correcting for them.

Still try a PCM reset first. Check wiring at IAC and TPS as well as MAP sensor.
I do agree a vacuum leak can do this as well, but you said it did this prior to manifold removal correct?:dontknow:
 
beastly1 said:
just plugged off the iac and it runs poorly won't even idle raised the idle screw and it will idle, now what???? is my iac bad ??? 85 bux at autozone[/QUOTE

PLUGGING THE IAC WILL RUN LIKE SHIAT!!!! IT HAS TO BREATHE TO RUN THE ENGINE!!!!:chain:
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VENOMOUS1 said:
Whoa -whoa-whoa guys!!!! DONT GET HIM ADJUSTING THE TB BLADES as you will throw of the TPS sensors determined idle! THE IAC IS SUPPOSED TO LET THE ENGINE BREATH AT IDLE AND WILL SUCK A LOT OF AIR!! AND IF YOU PINCH IT OFF, OF COURSE IT WILL KILL THE ENGINE! IT'S JOB IS TO FEED THE ENGINE AIR WHEN YOU LET OFF THE THROTTLE AND AT IDLE, BECAUSE YOUR THROTTLE BLADE IS CLOSED CHOKING THE ENGINE. THE IDLE AIR CONTROL VALVE LET'S THE AIR IN TO KEEP THE ENGINE IDLING AND HAPPY!

I do think it could be a faulty IAC though. You also should look at all wiring because the MAP could do the same type thing with the idle. It could be measuring false readings in the manifold and correcting for them.

Still try a PCM reset first. Check wiring at IAC and TPS as well as MAP sensor.
I do agree a vacuum leak can do this as well, but you said it did this prior to manifold removal correct?:dontknow:
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Lol calm down man, See my video up there. Completely blocked of mine still idles. It idles down, but does not shut off or run ragged. WHen you release it, it idles high and then settles down, showing that the IAC is functioning. The iac is there to maintain idle and make adjustments when the ac compressor comes on. But it is not intended to be the soul source of air when at idle. There is a idle adjustment screw on the TB intended to set the base idle. The tps is not sensitive enough to register a voltage change of the 1/10th of a degree to allow some flow of air around the throttle body butterfly,

Alot of those that have purchased the Roe or xmetal single blade got the idle surge. Even the instructions explain this, and show how to adjust the throttle screw to smooth out this surge.
 
VENOMOUS1 said:
Your throttle blades are open too far IMO because blocking the IAC airway should indeed kill the engine.:dontknow:
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Mine is perfectly fine. Idles like a champ. It is 1/4 of a turn from the stop. Roe suggest 2 turns. The photo Sean Roe supplied with the TB shows the gap being larger than mine. I also did not modify my blade like some have by sanding the edge down. I went a little on the adjustment as i could to maintain perfect idle with the IAC normal'd up. You should go try the test yourself. We have a member on here that has his IAC unplugged and keeps his idle adjusted via the set screw only.
His name was Stanimal. After reading his thread 3 years ago i did the same to my 05 with the OE TB for 1 week to see what effect it would have on the pop on decel.
Here is the linkhttp://www.vtcoa.com/forums/f7/idle-speed-16551/#post352586



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JeffBoyette said:
Mine is perfectly fine. Idles like a champ. It is 1/4 of a turn from the stop. Roe suggest 2 turns. The photo Sean Roe supplied with the TB shows the gap being larger than mine. I also did not modify my blade like some have by sanding the edge down. I went a little on the adjustment as i could to maintain perfect idle with the IAC normal'd up. You should go try the test yourself. We have a member on here that has his IAC unplugged and keeps his idle adjusted via the set screw only. Ill have to do a search to find the dudes name, but there was a thread on it.
View attachment 48340
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All I can say Jeff is that you will change the TPS setting as I have watched it during playing with the set screw long ago on my factory TB. It can put the engine into fueling maps intended for part throttle rather than idle. You can watch the voltage rise as you open the blades. The PCM likes a certain value at idle and I'm sure has a couple volts either way that are safe, but you can get into part throttle maps real fast then your getting too much gas at idle.:burnout:
 
JeffBoyette said:
Mine is perfectly fine. Idles like a champ. It is 1/4 of a turn from the stop. Roe suggest 2 turns. The photo Sean Roe supplied with the TB shows the gap being larger than mine. I also did not modify my blade like some have by sanding the edge down. I went a little on the adjustment as i could to maintain perfect idle with the IAC normal'd up. You should go try the test yourself. We have a member on here that has his IAC unplugged and keeps his idle adjusted via the set screw only.
His name was Stanimal. After reading his thread 3 years ago i did the same to my 05 with the OE TB for 1 week to see what effect it would have on the pop on decel.
Here is the linkhttp://www.vtcoa.com/forums/f7/idle-speed-16551/#post352586



View attachment 48340
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I read that thread and don't think he meant he removed it altogether.:dontknow: Like FSTJACK said, it adjusts the TPS voltage but not idle. It may change your idle for a second, but will return via programmed idle in the PCM. That was odd he talked of idling at 3-400 RPM though. Weird?:dontknow:
 
Agreed. To clarify my suggestion earlier. Im not intending you to turn the screw 6 or 8 revolutions.

After watching beastly's video you will notice that the truck, upon immediate startup idles at around 800 which is a little high if it isnt freezing outside. After it settles down, it drops below 600 and surges up to 750- and back and forth

The IAC causes this NOT A VACUUM LEAK. The IAC is a stepper motor. It is closing to settle the idle down, and there isnt enough air getting by the tb, so it opens up too far, and goes back and forth trying to maintain.
 
VENOMOUS1 said:
I read that thread and don't think he meant he removed it altogether.:dontknow: Like FSTJACK said, it adjusts the TPS voltage but not idle. It may change your idle for a second, but will return via programmed idle in the PCM. That was odd he talked of idling at 3-400 RPM though. Weird?:dontknow:
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While you IAC is connected and working properly, adjusting your throttle set screw will do nothing. If you let more air in by the throttle body blades, the IAC will still attempt to maintain that idle and all you did was change the tps voltage. However his was completely disconnected. I talked to him via pm years back. 3-400 is way to low, not enough oil pressure there. If the IAC is disconnected it doesnt matter what the pcm wants it to do, it has no physical way to introduce more air into the engine. Thats how he was able to set the RPM of idle with the set screw.
 
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Found this, ronnie was referencing another post about touching the battery cables together 10 minutes to reset the ECU
rottenronnie said:
When my t.p.s. went south and the engine was only seeing 70% throttle, I was swapping e.c.u.s back and forth between stock and the DC stage 2 flash back then-(the days before the SCT) and I didn't really notice much of a power difference with either e.c.u., EVEN WITH THE NEW T.P.S. INSTALLED Hmmmmmmmm?????..... That was because the data from the old defective t.p.s. was being retained in BOTH of the e.c.u.s. The check engine light didn't even trip there was a problem with the data from the t.p.s. 'cause it was still working, at least, I guess, and must have still been within range of the data the e.c.u. would accept.

It wasn't until I rebooted each of the e.c.us. that the power returned to normal levels in each box. The change was immediate.

10 minutes, I haven't tried before but it couldn't hurt....

Ronnie
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Another thing you can try instead of blocking off the IAC... is while it is surging, unplug the IAC. If the surging stops you know it is compensating.
 
JeffBoyette said:
His was completely disconnected. I talked to him via pm years back. 3-400 is way to low, not enough oil pressure there. If the IAC is disconnected it doesnt matter what the pcm wants it to do, it has no physical way to introduce more air into the engine. Thats how he was able to set the RPM of idle with the set screw.
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I gotcha, apparently he filled the seat area for the plunger of the IAC and strictly used the TB blades for idle. Hmmmm.....I could see his idea of faster throttle response as the idle would return quicker than the IAC valve can move just by the spring on the TB blades. But again, it throws the TPS out a few 10ths of a volt therefore putting it the fueling past normal idle maps:dontknow:
And a vacuum leak CAN affect the IAC because the MAP reading will be lower than normal and the PCM will try to adjust the IAC to compensate and it can be a up/down idle because of the PCM continually correcting for idle air, the IAC correcting, then the PCM says everything is good, then MAP sees a vacuum leak again and corrects the IAC again in a repetitive process.

I still am not sure his problem is a vacuum leak though:dontknow:
Great knowledge you have there though Jeff. Maybe we'll both learn something?
 
will that mean that my iac is bad or will it be something else, write now i disconnected both leads on the battery and held them together for 30 seconds and connected back up to the battery. will start it in the morning when it is cold. will try unplugging the iac and see what happens. this blows:chain: if i had a vacum leak would'nt run like crap all the time, and get a cel also.
 
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VENOMOUS1 said:
I gotcha, apparently he filled the seat area for the plunger of the IAC and strictly used the TB blades for idle. Hmmmm.....I could see his idea of faster throttle response as the idle would return quicker than the IAC valve can move just by the spring on the TB blades. But again, it throws the TPS out a few 10ths of a volt therefore putting it the fueling past normal idle maps:dontknow:
And a vacuum leak CAN affect the IAC because the MAP reading will be lower than normal and the PCM will try to adjust the IAC to compensate and it can be a up/down idle because of the PCM continually correcting for idle air, the IAC correcting, then the PCM says everything is good, then MAP sees a vacuum leak again and corrects the IAC again in a repetitive process.

I still am not sure his problem is a vacuum leak though:dontknow:
Great knowledge you have there though Jeff. Maybe we'll both learn something?
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I just went to the truck, pulled the rear vacuum tube off that goes to the power brake boost, and using my thumb, tried to hold varying amounts of vaccum leak. I could not get it to surge, but i could get it to idle very high.

Vaccum leaks on these trucks are going to happen either from the rear port i discussed, or the small hose that connects to the bottom of the intake by the tb. A cracked hose, or coming lose.

The rear one does not allow any air flow, however it provides a vacuum source. if it was leaking bad enough to cause this issue, he may lose power brakes. The one on the front runs to the evaporative emmissions control system for the fuel tank vapors. That system will only allow fuel vapors to be burned while the engine warm and not at idle or wot, so cruising. if anything was wrong with that system, it would pop a code. If the hose was loose under the tb you wouldnt have a EVAP code, but it would flow enough air that the IAC wouldnt be able to compensate causing a surge. Finally the gasket wouldnt be leaking on the TB or the Intake because the symptoms were before they were removed from the vehicle, nor would they flow enough air to cause the problem.

Sure vacuum leaks can cause surge on some vehicle. However our vehicle doesnt have alot of the other possible leak points and emissions controls like EGR. And our idle control system uses a port behind the throttle, while some older vehicles use a solenoid connected to the throttle body blade to adjust idle.
 
beastly1 said:
will that mean that my iac is bad or will it be something else, write now i disconnected both leads on the battery and held them together for 30 seconds and connected back up to the battery. will start it in the morning when it is cold. will try unplugging the iac and see what happens. this blows:chain: if i had a vacum leak would'nt run like crap all the time, and get a cel also.
Click to expand...

If you had a vaccum leak, you would likely throw a code. You would have a high idle, it would sense a lean condition, and an improper manifold pressure.

The reason you dont have a code now, is the idle is being caused by the computer and the computer expects the results its getting. It wants the IAC to open, it does, it idles high, it wants it to close, it does, it idles down. It is within acceptable parameters.
 
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