Ok time for a new thread with and old problem:
I have no fast idle on my 3.9L/ Auto Dakota, and need some help figuring it out!!!


So far I've changed:
IAC
TPS
Cranshaft position sensor
coil (again)
MAP
EGR
the lower (one wire) temperature switch
the upper (two wire) temp sensor fell within limits of 500-1100 ohm (engine cold) that the Haynes book stated

My truck had a complete tune up plugs, wires, dist. cap, rotor button, etc. in march of this year as well.

This has been a problem with my truck since I got it a year ago, oh if anyone is wondering if I get any codes from it......
NOPE no codes I've checked it 3 or 4 times now when cold and after I've driven it most of the day.

Any and all suggestions/help would be appreciated.

 

What exactly do you mean by fast Idle? Is your idle always low, like 200 RPM's or so? Are you stalling? Describe the problem more! The IAC is the typical reason for bad idle issues. Even new they are bad. 95_318SLT replaced his with 4 new ones before it ran right.

 

When I first start it in the morning it should go into a fast idle mode, since it's been getting down in the upper 40's here in NY already. And last winter it never went into the fast idle mode when starting it in the morning or even after it has sat for awhile. What should I do, take the IAC back and have it replaced? I got if from Auto-Zone and it has a 2 year warranty, don't really want to buy another as there $54.56 a piece.

It idles between 600 & 800 rpm when I start it and will stay running, it doesn't stall out at all even when fast release on the gas pedal, or when coming to a red light. It just does not have a fast idle to it when cold to allow it to warm quicker.
Any suggestions other than taking the IAC back? I'll take it back just for the purpose of making sure that it's not bad.

 

That is perfect idle. As for a when it is cold and has a high Idle, I don't think mine ever will go above 800 even at 20 deg.

I think it is fine. If it is always at 600-800 that even might be to high rpms in warmer temps.

Also if your do have a problem in cold temps your 2 wire coolant sensor may be the problem. You said at cold it tested good. But how about at higher temps? Just replace it if you think you have a problem. It is only $10. The 1 wire is only for the gauge. The 2 wire is for the computer.

 

I thought that the fast idle should be about 1200 - 1500 rpm so that the engine could warm to normal operating temps quicker, of course I'm just guessing as Rob's, 2002 Ford Ranger when it starts on the cold mornings runs right around 1300 rpm and as it warms up it idles itself down to around 750 rpm in Park or Neutral and when put into reverse or drive it goes to around 650 rpm.
I just looked up the two wire coolant temp on Auto-Zone and it's $20 must be stuff is cheaper where you live.
I'll replace it and see what happens.
Thanks for the info, I thought that the one wire went to the computer, I will have Rob test the two wire temp sensor as the book says it should be 1300 ohm or more at normal operating temps, but anyhow I'll change it just to say I did, after all I changed everything else.

 

My 93 Dak 4X4 LE with V8 only idles around 800 at cold start up...but it's summer here in Tejas with highs of 98-103 and lows of 65-70 degrees. After 3 or 4 minutes, it idles down gradually to 600 rpm in Park but will drop down around 500 rpm when in D or R. Can't remember where the cold idle was back in winter, but I know it wasn't more than 1000. Have you checked your thermostat? You can pull it and drop in a pan of water on the stove to check it...turn the burner on and see if it pops open when the water heats up.