IAC adjustment and TPS voltage check?
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Champion
Joined: Jul 2005
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From: Greeneville, TN
IAC adjustment and TPS voltage check?
Sean seems to think my weird idle problem in my other thread is the IAC needs adjusted. IIRC we can't do that right? He also said I should check the TPS voltage and make sure it's .76 volts. How do I do that?
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From: Clayton MI
On the TPS connector, insert probes into cavity 2 (orange wire with dark blue trace) and 3 (black with light blue trace) and read voltage. (if it's a negative number, switch your probes...) with throttle closed, the voltage can be as low as .26 volts....... and as you open the throttle, should scale smoothly to 4.5 volts.
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Legend
Joined: Jul 2007
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From: DFW, Texas
You really need a scanner to adjust the Idle air counts, otherwise it's a bunch of trial and error. This is how it was explained to me:
Essentially what you are doing is adjusting the truck's minimum idle and how quickly the IAC valve recovers when you let off the throttle.
Minimum idle should be about 100rpms below the truck's PCM set target idle RPM. If the truck's PCM attempts to hold idle at 750rpms, you should set the throttle plates so that the truck idles around 650rpms.
The reasoning behind this is as you let off the throttle, The PCM will adjust the IAC to maintain a preprogrammed idle speed. If you set the truck's minimum idle too close to the PCM idle and you are off just a bit, the PCM will throw fits and constantly adjust the IAC to attempt to lock in on the correct programmed idle. Each correction by the PCM of the IAC is a "count." The more counts, the longer the truck takes to adjust and stabilize idle. Too high a count, and the rpm needle drops very slowly as you let off the gas, almost as if it is floating down to the idle rpms. This sucks for braking, as the engine is still pushing the truck forward. 100 or so rpm's below the PCM's set idle allows wiggle room for vac leaks and the like.
The easiest way I have found to do this is:
1. Start engine, idle, and allow it to warm up in park with the parking/hill brake ON.
2. Unplug the brake booster line, and wait about 10 seconds. This will force the idle HIGH. The PCM will attempt to compensate by completely closing the IAC. This is good for setting the minimum idle.
3. Reach behind the TB and unplug the IAC while the engine is still running. BE CAREFUL! This will keep the IAC from reopening so you can set the minimum idle.
4. Slowly reconnect the Brake booster line. The RPM's should drop down pretty low as the vac leak is now sealed, and the IAC cannot reopen as it is unplugged.
5. At the front of the TB is the throttle plate adjustment screw. It is a #25 torx screw. This set screw will allow you to open or close the throttle plates very small amounts. On the stock TB, there is a small aluminum plug you may have to remove to access this screw. you can drill into it a very small amount with a small screw and then pull on the screw with a pair of pliers to extract it. See this link for a location:
http://www.bionicdodge.com/Download/...a%20Magnum.pdf
6.Using a scanner that can monitor rpm's adjust the idle using the set screw to about 650rpms. Without a scanner, you're kind of just guessing, but there is a breaking point where the engine will really drop low on the idle, that's where you want to be. Be VERY careful not to let the truck stall out by closing the plates too much. If you do this, you'll have to open the plates again and restart the truck. This can lead to you opening too much and losing track of what the stock idle "sounds" like, causing all sorts of hell. This is the reason I STRONGLY suggest you use a scanner.
7. After the minimum idle is set, turn off the truck. Plug the IAC back in and restart the engine. The truck's RPMs should flare up and then settle back down. This is the PCM trying to raise the RPMs and then settle back in. This process is actually setting the Idle Air Counts. A good scanner can tell you exactly how many counts it takes, so the article above gives you a range to aim for.
8. Take the truck out for a spin. Give it some gas and watch the tach needle; it should drop quickly and immediately after you let up on the throttle.
One thing to note about that article I linked: it mentions an idle of about 750-800. I have tried that many times and it didn't work right. The motor and PCM he was working with at the time was not stock and set for a higher idle on purpose, that high of an idle causes trouble on a basically stock motor.
Essentially what you are doing is adjusting the truck's minimum idle and how quickly the IAC valve recovers when you let off the throttle.
Minimum idle should be about 100rpms below the truck's PCM set target idle RPM. If the truck's PCM attempts to hold idle at 750rpms, you should set the throttle plates so that the truck idles around 650rpms.
The reasoning behind this is as you let off the throttle, The PCM will adjust the IAC to maintain a preprogrammed idle speed. If you set the truck's minimum idle too close to the PCM idle and you are off just a bit, the PCM will throw fits and constantly adjust the IAC to attempt to lock in on the correct programmed idle. Each correction by the PCM of the IAC is a "count." The more counts, the longer the truck takes to adjust and stabilize idle. Too high a count, and the rpm needle drops very slowly as you let off the gas, almost as if it is floating down to the idle rpms. This sucks for braking, as the engine is still pushing the truck forward. 100 or so rpm's below the PCM's set idle allows wiggle room for vac leaks and the like.
The easiest way I have found to do this is:
1. Start engine, idle, and allow it to warm up in park with the parking/hill brake ON.
2. Unplug the brake booster line, and wait about 10 seconds. This will force the idle HIGH. The PCM will attempt to compensate by completely closing the IAC. This is good for setting the minimum idle.
3. Reach behind the TB and unplug the IAC while the engine is still running. BE CAREFUL! This will keep the IAC from reopening so you can set the minimum idle.
4. Slowly reconnect the Brake booster line. The RPM's should drop down pretty low as the vac leak is now sealed, and the IAC cannot reopen as it is unplugged.
5. At the front of the TB is the throttle plate adjustment screw. It is a #25 torx screw. This set screw will allow you to open or close the throttle plates very small amounts. On the stock TB, there is a small aluminum plug you may have to remove to access this screw. you can drill into it a very small amount with a small screw and then pull on the screw with a pair of pliers to extract it. See this link for a location:
http://www.bionicdodge.com/Download/...a%20Magnum.pdf
6.Using a scanner that can monitor rpm's adjust the idle using the set screw to about 650rpms. Without a scanner, you're kind of just guessing, but there is a breaking point where the engine will really drop low on the idle, that's where you want to be. Be VERY careful not to let the truck stall out by closing the plates too much. If you do this, you'll have to open the plates again and restart the truck. This can lead to you opening too much and losing track of what the stock idle "sounds" like, causing all sorts of hell. This is the reason I STRONGLY suggest you use a scanner.
7. After the minimum idle is set, turn off the truck. Plug the IAC back in and restart the engine. The truck's RPMs should flare up and then settle back down. This is the PCM trying to raise the RPMs and then settle back in. This process is actually setting the Idle Air Counts. A good scanner can tell you exactly how many counts it takes, so the article above gives you a range to aim for.
8. Take the truck out for a spin. Give it some gas and watch the tach needle; it should drop quickly and immediately after you let up on the throttle.
One thing to note about that article I linked: it mentions an idle of about 750-800. I have tried that many times and it didn't work right. The motor and PCM he was working with at the time was not stock and set for a higher idle on purpose, that high of an idle causes trouble on a basically stock motor.
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Thread Starter
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Champion
Joined: Jul 2005
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From: Greeneville, TN
Well I checked the TPS volts and it was 0.08 key on and off. When I started it the volts were 5.17. After starting it i had readings of 5.17-5.18. That tps adjust site makes no f-ing sense at all. There's no way to change it. It was fine before why would it need adjusted now? Maybe replaced????
NOW i have a dumb question. My truck goes in to get the AC charged tomorrow. If I have the garage set the idle, then Sean sends me a new tune....won't that screw it all up again???
NOW i have a dumb question. My truck goes in to get the AC charged tomorrow. If I have the garage set the idle, then Sean sends me a new tune....won't that screw it all up again???
Thread Starter
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Champion
Joined: Jul 2005
Posts: 2,966
Likes: 3
From: Greeneville, TN
Was all ready to order a TPS. IAC, and MAP sensor tonight but was called back to work. I decided to give my first tune a try and see what would happen. Truck fired right up and idled fine. The A/F is a little wacky but the idle is perfect hardly moved at all. I sent Sean a email letting him know about that so maybe it is a tune issue.
Would a tune throw the TPS volts off though?
Would a tune throw the TPS volts off though?