Maybe the passages in the intake manifold where the IAC bolts to are clogged with crap. That's all I can think of at the moment, but will think on it a while and try to come up with something else.

 

I'm still thinking out loud here... Chilton specs the idle for an auto trans at 650rpm - is that in park or drive? I have mine set (tinkered a bit more last night) so it lands at 650 after it settles into drive. Note previous post about dropping rpm after being in gear for awhile. It idles at about 800rpm in park.

One thing worth mentioning - when I had the idle set way high, the truck would really dip in rpm when it engaged in gear, sometimes enough to try to die. Seems like 500rpm or so is about the low limit before it can't keep itself running. I'm wondering if that's going on with your truck too?

 

I pulled the TPS and had it tested, tested fine. I followed these instructions from May '08. The truck will now hold idle in reverse and drive most of the time. Pulled the codes and it's clean but for the VSS. I could tell on my drive it wasn't shifting down. Tomorrow I'll tackle that again. Does anyone have a favorite EZ PZ way to locate shorts. Anyone know how many connections are on the VSS line from the pumpkin to the computer?

How to set the TPS, (throttle postion sensor)

You want the TPS voltage to be set under 1 volt. Setting it to .93 to .98 is good range and should be fine. The risk of a surging idle increases quickly the closer you get to 1 Volt.

Loosening the two bolts on top of the TPS, this will enable you to turn the sensor slightly left to right. This is how you adjust it. Now you will have to back probe the black wire (negative) and the green wire (positive) of the sensor with a multi-meter. In some cases the bolt holes of the TPS might need to be elongated to achieve the proper voltage reading.

Resetting the cars computer and idle relearn

Set your timing to where you want it, 10* is stock, advancing a little to 12*-14* might be good, withuot pinging.
Now reset the cars computer.
Do this by disconnection the battery for 20 minutes, with the headlight switch in the "on" postion. Turn off lights and reconnect battery, unplug IAC motor, and start the car. The motor may have a hard time starting and you may need to give it a little gas to stabilize the idle. Once the idle settles, adjust the idle stop screw between about 700-800 rpms. Now adjust the TPS voltage to .94v-.98v.
Shut car off. Plug IAC motor back in and start the car.
Let it idle for 2 minutes with all electrical accessories running.
Shut engine off for 2 minutes.
Let it idle again for 2 minutes with no accessories running.

 

This is good info - I had run across the TPS info before, but not the other... I'll have to try that (when it's not snowing like crazy).

There should only be a connector at the VSS and another on the fenderwell before you get to the multi-pin connector to the computer itself.

 

With an automatic transmission the idle is set in Drive.

 

OK - now you've got my interest.

Let's see... set the parking brake, put it in drive, hope the brake holds while you stand in front of the truck, and adjust the throttle stop screw?

Is there another way to adjust it with the E4OD?

 

Have a buddy hold the brake, or park against a wall.

 

Any tips on the EEC? Pull the 10mm bolt, is anything else keeping it attached? Buddy between wall and bumper?

 

Snowing out, go figure. Who'd a thunk it this time of year?

 

Yeah, snow is just wonderful...

I have my garage full of parts of an old car that I'm parting out, so I can't get the truck inside to work on it. This weather is cramping my style!

Back to this adjustment - is this still adjusting the throttle stop while the truck is in drive (and hoping the e-brake holds), or is there somewhere else to adjust it?