My Dakota revs up to around 2000 rpms occasionally when I have the heater or ac on. If I turn off the ac or heater while it is happening it will idle back down to normal

 

Throttle body has been cleaned and IAC valve, tps, and map sensor have all been replaced

 

Check for a vacuum leak inside the cab, after the HVAC control valve.

This sounds like a vacuum leak that causes the ECU to enrich the mixture ... so, since it only happens when the heater or A/C is own, I'd look at vacuum lines downstream of the HVAC control.

RwP

 

I have suspected a vacum leak is there a good way to diagnose this to pinpoint where it's at exactly?

 

A smoke test - where you take a smoke machine and pressurize the inlet plenum for the truck. You then look for where smoke is coming out.

There's articles on using a fog machine to make a smoke machine. Also, if you, or a friend, is a smoker, there's always the "Big suck on a cigar, blow into a hose" method *grins*

But a super quick test - find the vacuum line going into the cab for the HVAC controls, disconnect it from the engine, and plug the engine side. See if it revs up then.

If it does, it's not vacuum, but the ECU activating the IAC ... and now it's time to check the IAC to see why it revs it that far.

RwP

 

I have done the test of pulling the line off the engine and plugging the port on the engine and it did not rev up.

 

In which case, it's the inside hoses that are bad.

Loverly.

I suggest studying how to curse in at least three more languages, then plan on pulling the dash so you can pull the HVAC box so you can check all the vacuum plumbing. (Cursing doesn't make it go any smoother, but it's a nice emotional release *grins* ) Although, you may get lucky if you can lay on the floor looking up - you may find a unplugged hose. Try that first. Suggestion: If you pull it, order a heater core so you can replace that while it's out.

Although, you may get lucky - check the lines into the HVAC control unit, and see if they have any breaks there.

Now, just to recap and because I wasn't clear - the engine speed didn't change as you activated the A/C or heat with the line plugged, like it does when the line is connected, right?

RwP

 

Well the engine speed changed just slightly like u would expect it to when the PCM adjusts the IAC valve but it never did rev up. And well the heater core isn't even a year old BC I changed it myself already lol. What about the vacum check valve on the line right by the engine? Could it cause the kind of symptom I have?

 

Did you disconnect before, or after, the check valve? However, easy to test - disconnect after the check valve, does it rev like that? Plug it, does it drop back down?

And when it's down, does manipulating the HVAC controls cause it to rev up and down?

The sticker in my head about it being the check valve is that it takes manipulating the HVAC controls to cause it to rev like that. I'd not expect it to go to 2,000 RPM ... but another hint is the "heater core isn't even a year old BC I changed it myself already lol." At what point did it start the revving? I'd double check the vacuum lines.

Having had the dash out you're familiar with why I said "Loverly" and to study up how to curse in at least three more languages *grins*

But that also means you can probably pinpoint where the vacuum lines ARE ...

Check the FSM for how the vacuum lines are activated, and see what plan best matches what manipulation of controls causes the engine revs, and you'll have zeroed in on where the leak could be.

RwP

 

I pulled the whole hose off of the engine and stuck my finger on the engine port so I haven't really checked the vacum check valve. And having different controls activated doesn't seem to effect anything. The only time it has reved up is when the ac or heater it turned on in general. No difference if I have it on defrost or floor vents or both that makes no difference. And the reving never happened till after the heater core had been replaced but it didn't start happening instantly after. Several months went by before I had this issue. And yeah I know we'll of where everything ive just been trying to decide if it for sure is a vacum leak and pinpoint where it is located.