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Discussion Starter #1
Hello! First time poster here, so please forgive me if I make any major mistakes about posting :)

I have a 2001 ram 1500 with a 318 and 5 speed manual. We just replaced the engine about a thousand miles ago (block and both heads). The problem is that the truck idles high (about 1500 RPM) when in neutral and rolling down the road. The idle will drop to normal when the engine is cold and the clutch is let out, but once it reaches a certain temp, if you let the clutch out or pop it out of gear at any speed above 5 MPH, the RPM will go to 1500 and remain there until you come to a complete stop. I can "nudge" the RPMs lower by putting it in a high gear and letting the clutch out to lug the engine. If I get it below 1500, it will drop to around 650 and remain low until I stop, when it finally drops to 550. I can also feel it pulling the truck along while in gear.

I know people will probably think TPS/IAC, but I have replaced both to no avail. The throttle body is clean. No check engine lights. The current TPS measures 0.6 volts at idle, and smoothly increases in voltage as you open the throttle. The TPS and IAC are both genuine mopar replacements, but I recently switched TPS to an aftermarket (to see if that was the problem.. no difference). It could be the TPS but I'd rather not drop another 40 bucks if I don't have to. I also disconnected and capped the vacuum line to the cruise control with no improvement.

I will also include a list of mods, as I am not sure if maybe I screwed something up with any of them: Hughes F1 airgap manifold, K&N cold air intake (w/ IAT relocated to the intake horn), injectors were recently sent out for cleaning, and a hemifever tune. Also, a 180 tstat and dual electric fan kit (deleted regular cooling fan/clutch). Also, I have a filter inline with the PCV valve and a breather installed on the other valve cover (as opposed to the valve cover hose connected to the air intake).

Any ideas how I could run this gremlin down? I don't know if it's just a sluggish piece of junk (318 and all) but it seems gutless and I get about 10 miles/gallon. I used to get closer to 15 miles/gallon.

Any help, ideas, or insight is greatly appreciated.
 

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How many miles on the throttle body? They can wear (throttle shaft to body) and create a vac leak that raises the idle. I would go over all the vac lines to make sure there are no leaks anywhere.
 

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Kilroy
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check all of your vacuum lines and caps ALSO retest your " NEW " IAC especially if it is aftermarket

I and many others on here have found that anything OTHER than genuine MOPAR
cant be trusted.. my aftermarket was 2 months old and quit working..
chased my tail until I read on here of the issues with aftermarket pieces
and sure enough it wasn't working right
 

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As others have said, sounds like a vac leak, would check/test intake and tb gaskets too.
... EVAP issue??
... Not a fan of inline filter in PCV valve line as element will become wet/restrictive; kinda similar for fresh air filter "mounted" directly on valve cover (use a hose to keep element up and away so it does not get oil wetted, as long as the hose always drains oil/mist back to cover); (catch can or stock is best).
... Am assuming fuel sync has been set.
... Codes were not mentioned, could do the "hard dump" below

=============================================
From a past DT thread...

You can do what is often called a "hard dump".

We (techs) often do this when we need to totally reset the ECU and either don't have the proper tool close by (too lazy to walk to toolbox and get it) or just are "in a hurry".

First, disconnect positive+ battery cable at the battery and ground it to the chassis. Yes, the POSITIVE CABLE.

Wait a few seconds, 30 won't kill ya.

Now reconnect the positive cable. Careful, no sparks now.

Get in the vehicle, turn ignition key to on (run) position, now depress fully and release the gas pedal 5 times to set the TPS to WOT. (Make sure the floor mats do not keep the pedal from going WFO)

Turn the key to off, wait a min, and you should have cleared everything in the ECU except for the factory programming.
=============================================

The hard dump does not effect the (factory) alarm, the only thing I noticed is my radio presets, as this method came from a working Chrysler tech, I doubt if there are any negative effects.
=============================================

... Could also try the "finger trick" in post 12

http://www.dodgetalk.com/forums/showthread.php?t=138174

Welcome to DT.
 

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Discussion Starter #5
As others have said, sounds like a vac leak, would check/test intake and tb gaskets too.
... EVAP issue??
... Not a fan of inline filter in PCV valve line as element will become wet/restrictive; kinda similar for fresh air filter "mounted" directly on valve cover (use a hose to keep element up and away so it does not get oil wetted, as long as the hose always drains oil/mist back to cover); (catch can or stock is best).
... Am assuming fuel sync has been set.
... Codes were not mentioned, could do the "hard dump" below

=============================================
From a past DT thread...

You can do what is often called a "hard dump".

We (techs) often do this when we need to totally reset the ECU and either don't have the proper tool close by (too lazy to walk to toolbox and get it) or just are "in a hurry".

First, disconnect positive+ battery cable at the battery and ground it to the chassis. Yes, the POSITIVE CABLE.

Wait a few seconds, 30 won't kill ya.

Now reconnect the positive cable. Careful, no sparks now.

Get in the vehicle, turn ignition key to on (run) position, now depress fully and release the gas pedal 5 times to set the TPS to WOT. (Make sure the floor mats do not keep the pedal from going WFO)

Turn the key to off, wait a min, and you should have cleared everything in the ECU except for the factory programming.
=============================================

The hard dump does not effect the (factory) alarm, the only thing I noticed is my radio presets, as this method came from a working Chrysler tech, I doubt if there are any negative effects.
=============================================

... Could also try the "finger trick" in post 12



Welcome to DT.
OK, so I was intrigued with "giving my truck the finger". I had given it the finger a number of times, just not in the IAC port. I tried this:

Warmed up to operating temp
Stuck my finger over the IAC port while running until the IAC withdraws completely and the engine dies
Then with the key still "ON", I disconnected the negative battery cable and let it sit for a few minutes before turning the key "OFF"
Then I let it sit for a few more minutes
Hooked battery cable back up, turned the key to "ON" and let the IAC cycle back to it's preferred position
Started the truck.

I ran it around my property and it definitely seemed to decelerate properly and hold the correct idle, even while moving above 10 MPH.

Then, I drove it next time and back to the same old problem. This seems to be a "learned" problem.

I even drove it with all vacuum accessories disconnected and had the same issue. Sprayed carb cleaner around the intake manifold and TB manifold with no noticeable change. So I am almost convinced it is not a vacuum issue. If it were, wouldn't it idle high all the time? The idle comes back down when you pull up to a stop sign. It also idles correctly when you start it. It is only when you pop it out of gear do you notice that RPMs seem to be set at 1500.

I have not set the fuel sync. I did not even know it had to be done! Is it better to take into a shop to do (against my religion), rent a scanner from autozone (will they have the right one?) or use the voltage method (set crank to V8 line at 0 degrees and then turn the distributor slightly with a multimeter on the pickup and set distributor at the point the pickup just measures 5 volts). Even if the fuel sync is off, would it cause this issue?

Before I order a new IAC (the replacement I bought was genuine mopar) I am going to take off the throttle body and check to see the IAC port isn't clogged with junk or that the TB gasket isn't pinched or something. If it looks all good, I am going to order a new TPS and IAC (both mopar) to hopefully rule that out.

I have also read threads about "setting" the new IAC. It had to do with taking the cap off the screw that sets the butterfly plate opening on the TB. Same screw you would set idle speed on an old carburetor. Could it be possible this needs to be set?

The fact that it idles correctly when you stop the truck would argue against a vacuum leak, right? And if I lug the engine and get the RPMs below 1000, it will not idle back up but sit around 700-900 until you stop, at which point it will drop to normal idle speed.

I am also going to test wires to and from IAC/TPS to the ECU. Hoping that maybe a wired got frayed or bent when we put the new motor in and that explains all of this.

Finally, I am amazed how many people spend their time offering advice with conceivably no benefit to themselves. Thank you for your critical thought and responses!
 

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It is only when you pop it out of gear do you notice that RPMs seem to be set at 1500.

have not set the fuel sync. Is it better to take into a shop to do (against my religion), rent a scanner from autozone (will they have the right one?) or use the voltage method Even if the fuel sync is off, would it cause this issue?

I have also read threads about "setting" the new IAC. It had to do with taking the cap off the screw that sets the butterfly plate opening on the TB. Same screw you would set idle speed on an old carburetor. Could it be possible this needs to be set?

Finally, I am amazed how many people spend their time offering advice with conceivably no benefit to themselves.
... Being it only happens when warmed up (closed loop) and only when it's popped out of gear seems to indicate learned behavior.
..Might be a MAP sensor issue (its short rubber line/elbow has a bad habit of rotting and leaking); PCM would recieve a low (false) vac signal and add fuel (PCM was still thinking trans is in gear and extra load/hill etc was causing low vac signal).

... From what I've "heard", fuel sync by the voltage/meter method gives mixed results.
..Being it's a new motor and a tight timing chain would not fell guilty about blowing a few bucks getting the fuel sync set "properly", if dealer still remembers how to use tool to do it (ya, rent/borrow/buddy the proper scanner and DIY, or find someone with tool that knows how to use it).
... At the least, pop the dizzy cap and do the "initial set"; turn crank CW till balancer mark is at TDC at top of comp stroke (rotor will be point towards no.1 terminal on cap), then rotate dizzy body till notch on cam sensor is directly underneath rotor; pic in post 2

http://www.dodgetalk.com/forums/showthread.php?t=527977&highlight=fuel+sync

... I forget the whole story about resetting throttle butterfly; being cold idle (open loop) and warm start/"idle" are both good I don't think it's the issue, but, have been wrong many times before.

... Benefit is all the stuff one learns (my issue is trying to remember it, good but short memory and all, lol).
..Helps avoid minor/major/costly/UNNECESSARY headaches; always good to be armed with info before opening something up, or ya can easily end up with a costly bill and a half repaired can of worms (think heaters, vac issues, frt axle work, auto trans, running issues due to batteries/charging/grounds and cam/crank sensors; and ya, then there's the fuel sync, myself and kinda sounds like you too first heard about it here on DT).
..Although it's kinda quiet around here since the changeover, lurking around here helps.
..Swap and build threads etc have a lot of creative people/info/ideas; from the very modern, to sometimes the most basic and simply forgotten/overlooked "stone and wheel" methods of the past. Welcome to DT.
 

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Discussion Starter #7
So wouldn't you know it.. vacuum leak after all. I conveniently forgot to mention I had installed the cable actuator for the front axle engagement. Either the vacuum cap fell off or I forgot to install both, because only one of the metal lines was capped. I took the throttle body off for another inspection and noticed the vacuum T fitting from the cruise control/evap vacuum line and then realized I totally forgot about this line. Much better throttle response and power. Thanks again!
 

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So wouldn't you know it.. vacuum leak after all. I conveniently forgot to mention I had installed the cable actuator for the front axle engagement. Either the vacuum cap fell off or I forgot to install both, because only one of the metal lines was capped. I took the throttle body off for another inspection and noticed the vacuum T fitting from the cruise control/evap vacuum line and then realized I totally forgot about this line. Much better throttle response and power. Thanks again!
Thanks for concluding the thread to help others!! Cheers ttmike42!!
 

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Since swapping from an auto to the coveted NV 4500, I plan to install a vacuum gauge on the steering column. E-bay has a gauge mount that replaces the top half of the steering column shroud. A vacuum gauge is very useful in spotting problems.
 
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