Cold start high idle, hunting and almost 1000 rpm when running

[BroncoBhadBhaby]

Ok so maybe this might sound like a broken record. After scowering the internet for weeks I still have yet to find a solution to my issue.

For about 3 months my truck 94 5.8 Bronco (recently converted to manual MDO5 was done in June 2019) has had an idle speed of 2000 - 2500 rpm on a cold start. It'll take it about a minute to drop. However once the truck is warm it ranges from 500 - 1000 rpms bad hunting. Not stalled or died.

Lately it's been stuck on 1000 when driving. When in idle it hunts. This happens even when everything is off AC, heater, light and radio. I have notice some loss in power as well.

Things I've done:

Normal maintenance (tune up, oil and coolant changes)

Replaced IAC 

Cleaned the throttle body

Change the broken gasket on throttle body

Checked coolant and oil for pudding there was none.

I want to go on and on about vac leaks but I replaced the IAC valve a buddy of mine said to unplug it and see if dies. Not only did it Not Die but also ran normal no high idle and it stopped hunting it ran just right to spec. I was confused I chose not to drive it that I've read some forums where people have and now their trucks don't turn on.

I have no codes on my dash yes it fully functional. 

I am sort of a novice mechanic when it comes to my bronco. 

Can someone please recommend a standard of procedure to help me get to the issue. PLEASE DO NOT suggest I using anything flammable to check for a leak not that I'm afraid I'd just rather not lol.

Thanks 

 

[miesk5]

Yo BroncoBhadBhaby,

Welcome!

See my Vacuum leak test in post #11 incl some jowens126 HVAC Control Panel pics/info @ https://www.fullsizebronco.com/threads/help-with-dtc-codes-and-idle.206824/

Excerpt;

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly.

Or Air Conditioning when in MAX mode may switch to Defrost

Look to rent an automotive smoke machine.  Pep Boys used to rent them.

 

[BroncoBhadBhaby]

Amazing thank you!!!!!!!!! I will get this done asap

 

[Motech]

With IAC disconnected, what is your steady idle speed? It should be pretty low, around 500 RPM or less. If it's higher than that, higher than 600, then I agree you probably have a vacuum leak. But if it is low, at 500 or less, you probably don't. What you probably have is a TPS close throttle failure that likely will not generate a check engine light, or very possibly an engine coolant temperature sensor that's either sensing air from low coolant or failing and telling the computer it's much colder than it really is. Both of those failures can cause your exact symptom as well as a big vacuum leak.