Quick little experiment--

[Turdle]

I'd like to know if you guys could report on this for me please?

When driving at speed and slowing for a stop--could you please shift your lever to "N" and coast to a stop. Hold the stop for 4 seconds--

Now, I want to know this--
Do your engine RPM's hang a bit high while rolling in Nuetral, then come down to normal idle when vehicle is held stopped?

Thanks

 

[kert0307]

I'm pretty sure mine goes to the standard idle speed when it's still rolling. I'll check for sure though.

 

[Rottie]

Yes it does. And i'll ask a couple of engineers at work Monday to find out why that is.

 

[JDraper]

It's designed that way to help lower emissions. When the throttle snaps closed, the engine would normally go waay rich for a second, expelling a lot of unburned fuel out the exhaust. By letting the idle hang and allowing air into the motor(via. the Idle Air Control valve), it burns the excess fuel off, so the emissions are better.

We've been going over this for a while over on the Mach boards. The Mach's suffer from it pretty badly in stock trim. An IAC restrictor plate fixes the hanging idle pretty well.

 

[Turdle]

It's designed that way to help lower emissions. When the throttle snaps closed, the engine would normally go waay rich for a second, expelling a lot of unburned fuel out the exhaust. By letting the idle hang and allowing air into the motor(via. the Idle Air Control valve), it burns the excess fuel off, so the emissions are better.

We've been going over this for a while over on the Mach boards. The Mach's suffer from it pretty badly in stock trim. An IAC restrictor plate fixes the hanging idle pretty well.

Jeff, this is kind of like the hanging idle--however the hanging idle goes away in a given amount of time. It will do this sitting in park-yes

In my scenario--the idle will stay raised as long as the vehicle is moving in neutral. It may be entirely ok but---

This is causing an issue with my truck

I want to find out what it is so I can address it when I get tuning--it has something to do with the truck rolling, and a different idle command, I just know it. I also think it has a lot to do with the MAF signal.
On my truck-when I let off the throttle to slow down from any speed above 50mph, I still get the vroom vroom vroom surge between 1200-1700 rpms--it stops when I stop the truck, but continues until I do so, or shift to neutral, where the idle will hang steady at 1500 until the vehicle is stopped.
Once the vehicle is completely stopped, the surging goes away along with the higher idle--

 

[JDraper]

Jon, another possibility is the TPS voltage. They can be very sensitive to slight voltage shifts. I'm gonna attach some threads for your reading pleasure...they are Mach threads, but may apply to your problem too..


http://www.mach1registry.org/forums/showthread.php?t=66076

http://www.mach1registry.org/forums/showthread.php?t=47549

Have you also considered a problem with the IAC? Try unplugging it and see if the problem stabilizes..you may end up with a slightly high or low idle, but it should be stable when the engine is warm with the IAC disconnected.

 

[sparkyXplorer]

JT I just got back from trying to get those new tips (won't be in till tues) and OMW home I tried this....

I only did it once and was crusing about 30mph, stop light ahead, I shifted it into nuetral and the rpm's went to approx 1k, I continued to slow down till I was completly stopped and the Rpm's sat at 1k still...

I will try again from maybe some different speeds OMW to work...

 

[Turdle]

Jon, another possibility is the TPS voltage. They can be very sensitive to slight voltage shifts. I'm gonna attach some threads for your reading pleasure...they are Mach threads, but may apply to your problem too..


http://www.mach1registry.org/forums/showthread.php?t=66076

http://www.mach1registry.org/forums/showthread.php?t=47549

Have you also considered a problem with the IAC? Try unplugging it and see if the problem stabilizes..you may end up with a slightly high or low idle, but it should be stable when the engine is warm with the IAC disconnected.

Ive tried 2 tps-and 2 iac valves, I even had the plate thingy--
It has to do with the pro-m maf, the cam, and the stock tune-
If I adjust my maf tuner (not supposed to) it will stop the surging-
There is a transition thing right there in the PCM--
I'm just wanting to identify this so it can be eliminated--

 

[mawrazen]

I have been able to coast up to 7 miles or more down mountains between Atlanta and PA.

The idle hangs around 1k or more but slowly drops to about 750 RPMs

I would engage OD again after the truck reaches the speed limit or less.

Is this bad for the tranny?

 

[CDW6212R]

Interesting Jon, hopefully a new programming will stop that.

 

[briwayjones]

The Explorers with manual transmissions do this even. You can push in the clutch and continue to roll and instead of the RPMs returning to idle they will hover around 1200 RPM as long as you are rolling. They won't got back to idle speed until you stop for about 3 seconds.

 

[Turdle]

That's what I wanted--now I know it is normal.

 

[squish]

Mine is the same. unless completely stopped I can drive all over my neighborhood at around 1200 rpm and never touch the gas. Once the brakes are used for a few seconds and the truck actually sits still then it drops to just over 700 rpm. Bothered me for awhile but then I got used to it.

 

[carlover]

ive had several cars that do this, it can be annoying at times. I had a 96 dodge neon that i built the piss out of and a new computer program, throttle body, and lightened flywheel completely eliminated it. You have a computer tune right?? Larger bore throttle body?

 

[Dan Whitaker]

That's what I wanted--now I know it is normal.

And it only took you a little over a year to figure this out :