2004 Ford Ranger 3.0 Gas V6

I have this really annoying issue going on with my truck. On the initial cold start in the morning the idle will flare up to 2k RPMs and stay there. I had this going on in the fall and thought I fixed it but it's only started doing it since the outside temperature is above 40+ degrees.

In the fall of 2011 I replaced the Idle air control valve, cleaned the maf sensor, and changed the oil/filter. The issue seemed to go away. Now fast forward to last week before I changed my oil it flared up to 2k RPMs twice and I thought I hit the gas pedal both times. However, after the oil change it has been doing it every single time but it has also been warm like the 2 times it did it prior to the oil change. I checked vacuum lines and couldn't find any leaks. I believe if that was the case it would do it constantly.

Truck completely cold - it will rev up to 2k RPMs and hang there for a minute. Then the idle will back down to 1500 and sit there until the engine is warm. It's hell on the the brakes. Once the truck is warmed up (in open loop), it drives perfectly and the idles at 750rpms.

Truck Engine History
45k Shorty Headers added
45k Coolant Flush
50k Motorcraft spark plugs and wires
50k PCV changed
Engine flare started happening around 589xxk miles
59k Idle air control valve replaced, maf cleaned, and air filter changed
Motorcraft Oil Filter and Mobile 1 Synthetic Changed every 3k miles

Engine Coolant Temperature sensor? I'm stumped.

 

run thicker oil?

just kidding

It definitely sounds like unaccounted air is getting into the system. had this problem for the longest time, itd rev up near 2k for the first 3 minutes of start up. found a leak and now it revs to 1400 on start up

 

Where did you find your leak at? It may be a common area on Rangers.

 

well I had a slit in my air intake hose, like a razor blade cut and finding that brought revs down 400 at least and the other major one was a wire from my IAC got pinched between the throttle body and air intake tube and caused a gap in the seal between tube and plenum and pulling that wire out brought me back to normal.

those wont help you but goes to show, find the leak, solve the problem.

 

The air temperature sensor may be dirty/bad.
The PCM checks the sensor to decide how rich to make the fuel/air mixture at cold start.

 

did it do prior to the old iac? did u match up the EXACT same model?

 

I bought it from Ford, they matched it up off of my VIN number. The part looked identical.

The flare ups were happening prior to the IAC module.

I still haven't been able to locate a leak...

 

I worked on it after work and did the following.

Replaced the plastic vacuum line that runs the entire engine bay (I never did like the way Ford did that)
Put a gates hose clamp on the elbow that comes off the manifold
Cleaned out the PCV valve - Rattled just fine
Replaced the air filter
Cleaned the MAF with contact cleaner
Inspected every vacuum line and they all appeared to be intact
Reset the computer

One of these things must have fixed the issue because now the cold start idle is back to normal. I will see in the morning.