3.0 Idle wont drop below 3000

[jadwy916]

I just replaced a valve spring on cylinder 5, got everything put back together and it's working great except for the idle sitting right around 2500-3000.

I checked for vacuum leaks by spraying carb cleaner at every vacuum line I could see. But no change...

I'm thinking it must be a line I'm not seeing... But was wondering if any of you have had deal with anything similar?

Thanks,

 

[ratdude747]

I just replaced a valve spring on cylinder 5, got everything put back together and it's working great except for the idle sitting right around 2500-3000.

I checked for vacuum leaks by spraying carb cleaner at every vacuum line I could see. But no change...

I'm thinking it must be a line I'm not seeing... But was wondering if any of you have had deal with anything similar?

Thanks,

Probably not a vacuum leak... in my experience idle would be all over the place with such leaks on the 3.0. But that's just my experience.

That said, what did cause this happen to me in the past was a jammed IAC valve. In my case it was due to some sort of bug nest in the intake (previous owner ran it /o an air filter) that fragmented and a chunk made its way into the IAC. It was odd, took me a couple of days to discover why my idle was higher than the rockies...

Also verify that your throttle is indeed closed... always verify the obvious.

 

[jadwy916]

Thanks for the reply.

The IAC valve is new, but I'll take a look at it. Also, I'm going to get into the throttle today and check it out as well.

One of my friends (certified mechanic) asked if I tried simply driving the truck... A little scary, but maybe if I can't find a basic mechanical issue with the throttle body.

 

[ratdude747]

Thanks for the reply.

The IAC valve is new, but I'll take a look at it. Also, I'm going to get into the throttle today and check it out as well.

Did you replace the gasket? (they're sorta hard to find, so if you didn't that's ok if it was good). Bolts tight? What else in the intake (if any) have you worked with lately?

 

[RonD]

Check that throttle cable or Cruise control cable is not holding throttle plate open

Unplug the IAC valve while engine is running, it should close and idle should drop down to 500rpms or engine may even stall, either is correct.
If idle stays high then IAC valve is stuck open.
Remove IAC valve and check it, plugged it in while it is off the intake and turn on the key, IAC valve should open all the way and then close a bit.

"New" no longer means "it works"
New now means "never tested but warrantied", we are now the Quality Control Department for most manufacturers.

IAC valve uses a Step or Stepper Motor, computer sends it a "pulsed voltage", like a Morse Code, the various pulses tell motor to turn to its various "Steps", there are over 100 steps that can be "called on".
Step 20 might turn motor 90deg from 0
Step 40 180deg from 0
ect......
Each Step opens or closes the Valve connected to the motor a specific distance.

The Computer "Learns" which Step causes which RPM level, this is why the mechanic asked if you drove it, it allows the computer to "reLearn" what Steps to use on the new IAC Valve motor, but that can happen by just running the engine, no need to drive it, but it does need to warm up and cool down a few times(drive cycles).
New IAC valve will cause wandering lower RPM at idle as computer fine tunes which step sets what RPM, the above 2,000RPM is something else.

The high RPMs in your case reads like IAC Valve is simply opening all the way when powered up and computer has no control of it


Heads up: if you see what "looks like" and idle adjustment screw on the throttle linkage, don't adjust it, it isn't an idle screw.
Fuel injected engines can't use an idle screw since there are no "jets" like a carb had, the screw is for anti-dieseling and TPS(throttle position sensor) lower voltage adjustment.

If you have a volt meter set it for DC volts, with key on/engine off test voltage on TPS center wire, it should be .69 to .99volt, under 1volt, you can adjust that screw to get correct voltage if it is not in the above range.

 

[jadwy916]

Thank you all for your replies....

I hate to admit that I'm a complete idiot, but I have to.

I drove the truck to my local shop, no easy task with a 3000 RPM, and dropped it off. He called me this morning and told me I installed the stupid Idle Control Valve backward. And what's worse... I installed that before when the old one took a dump about 2 years ago!!! I should have known better!!!! After all the work I did, replacing the valve spring isn't exactly easy work, this is wear I lose it and drop the truck at the pro's....

Oh well, dunce hat for me. My Dad says I'm no longer allowed to work on anything built after 1966... hard to argue.

Thanks again everyone. You all are great!

 

[RonD]

Thank for the update

I didn't even know you could install IAC Valve backwards?
learn something new every day

 

[jadwy916]

Thank for the update

I didn't even know you could install IAC Valve backwards?
learn something new every day

Yeah, me neither, but that's what they said. I'm going to pick it up right now so I'll be able to see what's up.

Thanks again.