Idle issues with v8...

[shr3dd3r 09]

Just finished my v8 swap. 2000 Mountaineer 5.0 into 2000 Ranger. Had the computer flashed to get rid of extreme surging idle and auto tranny codes, but I am still having some minor issues. The truck is drivable but I am still working a few kinks out. Here goes, so bear with me...

On start-up it jumps to 1800 rpms and then falls to about 1400 and sounds relatively smooth but not perfect by any means. Not like it should sound anyway, it's a bit rough. While driving if I depress the clutch or coast in neutral the rpms jump up or down to about 1800 and then when I stop completely it falls to about 1400.

Here's the weird part....if I let it sit and idle at 1400 rpms for a few minutes (3-5 minutes) the rpms will drop all of a sudden to 500 and it sounds rough as hell, and almost like it's cammed. Then as soon as I get moving again the cycle repeats. Idle at 1800 until stopped, then 1400 for a few minutes, then 500 until moving again. Idle is always a bit rough.

Checklist:

TPS voltage is at 0.96.

Cleaned the IAC valve and throttle body and that didn't solve anything.

The IAC definitely works because it does drive differently with the electrical plug disconnected. Idle is even more sporadic.

I don't think there are any vacuum leaks.

The only thing I can think to do is replace the IAC altogether and see if that does it.

Suggestions? I'm at a loss...

 

[kimcrwbr1]

Did compare the wiring diagrams between the two engine computers and are all the inputs working. Have you cleaned the MAF sensor? only use electrical cleaner or rubbing alcohol. O2 sensor/s connected and is the cat/s in good shape. Are you swapping from a auto tranny to a manual maybe the computer is looking for inputs from the tranny wether in neutral or in gear I know earlier computers are tranny specific. I get pretty anal when it comes to wiring I check every wire is going where it is supposed to and also check for shorts. Get the engine schematics for both the mountaineer and ranger and compare them side to side you want all the proper inputs working for the 5.0 computer. I`m just assuming you put the 5.0 harness and computer in with the swap?

 

[shr3dd3r 09]

Did compare the wiring diagrams between the two engine computers and are all the inputs working. Have you cleaned the MAF sensor? only use electrical cleaner or rubbing alcohol. O2 sensor/s connected and is the cat/s in good shape. Are you swapping from a auto tranny to a manual maybe the computer is looking for inputs from the tranny wether in neutral or in gear I know earlier computers are tranny specific. I get pretty anal when it comes to wiring I check every wire is going where it is supposed to and also check for shorts. Get the engine schematics for both the mountaineer and ranger and compare them side to side you want all the proper inputs working for the 5.0 computer. I`m just assuming you put the 5.0 harness and computer in with the swap?

Haven't cleaned the MAF yet, but I do believe it is functioning correctly. O2 sensors are plugged in and the cats are in good shape. Yes I swapped from auto to manual but kept the auto computer. I had the computer flashed to remove the auto tranny codes and whatnot.

I had extremely bad surging idle before this, but now that is better. The idle is still a bit high, but I can't really adjust it so that it is lower because every now and then it drops below 500 as it is. The computer should think it's in neutral, because I hardwired that in the starting circuit so that I could start it with the manual tranny.

I tricked it into idling right by disconnecting the IAC, driving it, then reconnecting it and it idled perfectly at 700 rpms for several minute. But as soon as I drove it again I started having the same problem. Rough idle at three stages 1800 when coasting, 1400 when stopped, 500 after sitting still for 3-5 minutes. But cleaning the IAC did not solve the problem. Still don't know what else to check, unless the mechanic did not remove all of the auto tranny functions like he said he did.

 

[shr3dd3r 09]

Anyone have any suggestions? I just don't see how any of the automatic transmission functions would affect the idle speed like this. It had surging idle before and a hesitation every now and then, but that was fixed with the tune that supposedly removed all of the auto tranny functions.

Should I replace the IAC valve all together and see if that does it?

 

[Tominator]

Pull the codes.

 

[Teddyzee]

What is the base idle rpm? With the IAC unplugged?

 

[RangerSVT]

How did you tune it, and what did the tune consist of (what exactly was deleted)? My SCT allows me to user set the idle at both in drive and neutral. Even though you have a base idle, what was it set at with the tune? Who tuned it, are they trained and an authorized dealer/tuner?

SVT

 

[kimcrwbr1]

There is also a clutch switch that is a input to the ECM I am not sure that has anything to do with engine idle. Clean the MAF and reset the computer by disconnecting the battery for 1/2 hr and make sure everything is connected before you start it up. Bring the engine up to operating temp and then pull the codes. Get a piece of vacuum tubing 2ft long and put one end in your ear and search around all the gaskets connections and hoses. The closer you get to a vacuum leak the louder the hissing be careful of moving parts.

 

[cammeddrz]

an auto trans ecm will raise the idle if it thinks you are in gear, in fact it does exactly what you are experiencing

in fact another guy who had this same problem initially described his issue like this:

it idles stupid high between shifts and as I coast but within a few seconds of coming to a complete stop it idles down to a more reasonable level.

whoever flashed your ecm may have missed something when they eliminated auto trans stuff

 

[shr3dd3r 09]

Greg at Speedy Dyno in Owensboro did the tune for me. He removed all auto tranny CEL's and torque converter info. Don't know the specific details but what he did resolved the extreme surging idle and hesitation I had. But I still have rough idle, which leads me to believe there is some other problem. I don't think he messed with the idle speed, that should still be set to stock specs.

The computer should think it's in neutral all the time because I hardwired that into the starting circuit. Even if it did think it was in drive it still shouldn't idle that high. Sounds to me like it is doing what it is supposed to do just to an extreme. Idles a little higher for brake assist and power steering until it stops then the rpms drop. what's weird is the low rough idle that happens after several minutes of idling. This happens with or without the IAC connected. Without it connected it is even lower.

Base idle with the IAC disconnected is 400-500 according to the tach and it sounds pretty darn rough. The rpms don't drop immediately though when I disconnect the IAC. It seems like it takes a minute or so for it to have any effect at all. But then when I plug it back in the idle surges slightly and comes to rest about 1000 rpms.

The EGR vacuum lines were hooked up backwards, so I swapped those. However, that did not fix my idling issue... Still dumbfounded.

 

[RangerSVT]

I know Gregg, he did my tune. Go back and talk to him and describe your issues. Most likely its in the tune and he can go in, look at the sensor's readings and retune it. Did you get an X3 or a livewire? If you have datalogging, it will be a good idea to record some info so he can write the best tune...


SVT

 

[Teddyzee]

I would set the idl speed to about 700rpm with the IAC disconnected. Using the TB screw.

 

[shr3dd3r 09]

I would set the idl speed to about 700rpm with the IAC disconnected. Using the TB screw.

That's the problem. Right now it idles at 1800 while coasting in neutral, 1400 when stopped, and 500 and rough after a few minutes. If I set the idle to 700without the IAC plugged in it shifts those three numbers above up 200 rpms each which is worse. Even with a higher base idle it still sputters. Yet it drives great with no issues. It's set as low as it can go right now and still be comfortable to drive.

Maybe it's in the tune like RangerSVT said. I will contact Greg and see what he thinks about it. I'm going to punch myself in the face if it ends up just being the IAC valve after all of this frustration. In any case I should get better mileage now that the EGR vacuum lines are actually hooked up right.

 

[kimcrwbr1]

Run the engine at about 1200 rpms and unplug the IAC then adjust the butterfly to where it idles about 650 rpms then plug in the IAC. When you take the throttle off idle it will close the IAC and unplugging it will keep it closed. Reset the computer by disconnecting the battery for 1/2 an hour and then the computer will set the new values. It just sounds like its searching for all the inputs to set the values.

 

[kimcrwbr1]

Better yet reading closer run it around 2000 rpms and unplug the IAC then set the engine idle You want the IAC all the way closed and unplugged to set the throttle butterfly position, then reset the computer by disconnecting the battery and make sure everything is plugged in when you start the motor.