Sulli8888

What controls the 5.0 motor to idle up a little while when you first start it? Mine stays the same about 600 rpm

Chris_1

iTrader: (1)

Idle air control on the side of the throttle body. Computer controls it. Good place to start.

Sulli8888

Thanks Chris for the reply. I did clean that and seen no difference. Anyway to check it without just buying a replacement?

fatcat343

The choke will make it idle high when it's cold and you first start it. Just tap the gas and it'll idle normal again.

Chris_1

iTrader: (1)

?? what year truck are we talking about here ?

Sulli8888

1991 f150 5.0,
Has no choke.......... Does the IAC raise the idle when cold or something else?

fltdriver

IAC controls air flow at idle (pretty much a new version of a choke). Computer controls the IAC causing higher idle until the ECT (Engine Coolant Temperature) sensor reads a standard operating temp of the coolant inside the engine.

To test the IAC:
First unplug the connector then start the truck (when completely cold), if your initial idle is different then your IAC is not functioning properly. To verify IAC solenoid is bad: Use an ohm meter to check the solenoid by attaching the positive lead to the VPWR (vehicle power pin) and the negative lead to the IAC pin.

• Your resistance reading should be between 7.0 ohms and 13.0 ohms. If your reading is off, your IAC solenoid is bad.

ECT sensor is only like $10-15 new on rockauto so if it's in question I would just replace it as it's probably original anyway. Make sure you get the sensor (what the ECM uses to read ECT) and not the sender (what your temp gauge uses to display the ECT)

Sulli8888

I have replaced the ECT sensor already last week. It fixed the hard to staRT flooding at startup. I will try to test the IAC like you said and see if that idle's it up on cold startup. Thanks

fltdriver

If the ETC is new, was it doing the low start-up idle before you replaced it? If no, what brand ETC did you get?

If the IAC checks out, and if you have some extra time, I would suggest going through and cleaning as many connectors as you can find/reach with some QUICK DRYING ELECTRONIC CLEANER ($4 a can @walmart). Spray the male end, clean contacts with a brush (stiff nylon or soft metal), respray male end and into the female end, then insert male into female multiple times to clean the female's contacts. Takes about 1-2 minutes per connector. Also clean up any body/chassis ground points you can find, sand eyelet/frame until shiny, use wire brush on bolt, re-assemble then coat with dielectric grease to prevent future corrosion. {doing the battery terminals at this time would be smart unless they are new}

Takes an hour or two to hit the majority of the connectors/grounds but you will save yourself some major headaches down the road by doing this. Countless times people come here with issues that turn out to be connector/ground related, this was one of the first things I did when I got my truck and haven't had any electrical related issues in a year and a half. I also swapped out all of my fuses, bought a bulk assortment online for $12.

Not saying that the cleaning will fix your problem, but I do recommend doing it before replacing anything else as this is one of the BEST P.M. steps for these trucks. 20+ years of road grime/oil/dust/water/salt/etc.. can make the electrical system very finicky.

Sulli8888

I will check out the test on the IAC this weekend. Runs good, starts good, all good except does not idle up at start up.