Purchased the truck Saturday.

1999 4 liter, automatic, 4x4.
mechanically the truck is stock.

When warm in park truck idles at 1000-1100.
Did a tune up. Plugs, wires, air filter, oil change, trans flush.
Cleaned the tb, and maf.
When the iac is unplugged the truck idles at 500-600.
So I replaced the iac. Did the idle relearn.
Still idles at 1000+.
Where should I check for common leaks?

 

Where are you seeing high idle? on a reader or the dash gauge? Gauge could be reading high.

 

Not a vacuum leak if warm engine RPMs are below 650 with IAC valve unplugged

Computer is setting the idle that high, but why?

I would invest in a Bluetooth OBD2 reader, assuming you have a smartphone or bluetooth tablet
Any vehicle sold in US or Canada from 1996 and up is required by law to use OBD2.
So not a Ford thing, or even US made thing
So if you(or friends) have other vehicles or will have in the future this is a handy tool for under $30

Like all computers the saying "garbage in/garbage out" applies to automotive units as well
Something is causing the computer to set this idle level

Computer reads RPMs from crank sensor
It reads engine temp from ECT sensor
It has pre-programmed "target idle RPMs" for all engine temperatures
It moves IAC Valve by pulsing its Ground wire to set "target RPMs"

Computer has an ECT sensor timer, if ECT sensor isn't changing values or isn't warming up to 180+degF it should turn on the CEL and let driver know there is an issue

You can view all the sensor and control data "Live" using the OBD2 Bluetooth reader

 

I'm quite familiar with live reading obd2 data. I've got a 540hp lightning that's tuned via laptop and sct software.

I'll order and obd dongle. I already have the torque app. I doubt my lightning x3 will read the data. Thanks.

 

Finally got an obd reader that works.
ecu is reading coolant temp. Air intake temp is correct. Throttle is correct.

Here's idle in neutral and in gear

this is neutral




This is in gear

 

So is your TPS reading the right voltages?

 

yes. .98 at idle as show bu the % on the app and my voktage meter. It sweeps cleanly too