Erratic high idle help, please!

[ActuallyaMazda]

I’d greatly appreciate pictures of where that port should be. They must’ve sealed it off somewhere. All 4.0’s regardless of what they were in should’ve come with EGR systems from factory, correct?

 

[tw205]

I would think so, but if I said yes, someone would probably tell me I'm wrong , so I won't give a definative answer. Your profile says Washington. Is that State or DC? I'm assuming state and the eastern side if you don't have inspections. Last I lived out there in the 90s they has by yearly inspections in Seattle area

 

[ActuallyaMazda]

That’s fair haha. Yes, it’s WA state and I’ve never had to do a state inspection at least where I live which is a bit of a smaller town. I’m headed home right now so I am going to check that EGR port on the intake manifold and see if there are any on the exhaust I missed. I know it only has one O2 sensor and the other side is plugged off.

 

[tw205]

I got a picture of the intake manifold from rockauto. I put a red arrow pointing at the EGR port. I will still throw up some pictures of mine in the morning. This is for a 95 ranger 4.0 so yours may be a completely different beast.

 

[ActuallyaMazda]

I’ll take a look for that. I found a picture of my exact manifold and I don’t see anything that jumps out at me as that EGR port you were showing me. Could it be elsewhere?

 

[tw205]

I was afraid of that. 95 was a change to a plastic manifold. I may have been leading you in the wrong direction all along.

 

[ActuallyaMazda]

All good! Like I said, anything helps narrow it down more.

 

[ActuallyaMazda]

Ok, update on everything! Today I went to check everything that was mentioned in the previous comments.
It doesn’t appear that I have any kind of EGR system related things anywhere. The exhaust manifolds have no place for an EGR pipe, nor does the intake manifold.
Bringing up to temperature on cold startup it actually acted like it normally does when it hasn’t been idling high. It idled at just above 1000 rpm which is what it sits at with no prior issue. I took it on a test drive for 10 miles around town and when I returned home, I put it in park and the idle shot up again.
I unplugged the IAC and it dropped to about 800 - 900 and definitely wasn’t acting like it wanted to stall out UNTIL I sprayed carb cleaner directly into the air filter about where the MAF sits. It dropped to almost a stall for a few moments and then rose back up. I also unplugged and capped off the PCV valve from the intake and verified it wasn’t leaking from the fitting. Then I adjusted the throttle screw a few turns outward. I marked the original placement of it just in case.
Plugging the IAC back in after all that it held at about 1600rpm. I killed the engine and restarted it and yet again it was hard to start and when it did start, it ran all the way up to 3000rpm before dropping down to about 1800-2000.
Any ideas? I rechecked every vacuum fitting, around the manifold gaskets, and around the injector gaskets with carb cleaner and the only thing that caused it to change in rpm was spraying directly into the top of the air filter close to the MAF. It’s a cone air filter with no box and if I spray on the bottom side of the filter it doesn’t exhibit as much noticeable change as when I spray the top.

 

[2011Supercab]

Last I lived out there in the 90s they has by yearly inspections in Seattle area

Washington stopped testing Jan. 1 2020

 

[ActuallyaMazda]

Next update:
I have started the truck twice today cold. Each time, it starts up normal and drops the idle to where it should be. I take it for a short drive and the moment I put it back in park the idle rises to about 2000 rpm. If I turn it off and restart warm, it shoots the idle to 3000 rpm and then drops it to 1100 before rising again to almost 2000rpm. Upon warm start, it starts very rough and will backfire pretty hard almost like the cylinders are flooded.
I purchased and innova ford code reader and with some careful wire jumping I got codes for the ECT sensor being out of range and the AIT being out of range. Also got check O2 sensor as well which makes sense since it’s missing one. I traced the sensors back to the ground and cleaned off the ground to no avail.
I’m still at a loss. Could it just outright be a bad PCM or could those sensors just both be bad and then once it gets warm it triggers the PCM to adjust for them being out of range?
Thoughts anyone?

 

[ActuallyaMazda]

Next update:
I have started the truck twice today cold. Each time, it starts up normal and drops the idle to where it should be. I take it for a short drive and the moment I put it back in park the idle rises to about 2000 rpm. If I turn it off and restart warm, it shoots the idle to 3000 rpm and then drops it to 1100 before rising again to almost 2000rpm. Upon warm start, it starts very rough and will backfire pretty hard almost like the cylinders are flooded.
I purchased and innova ford code reader and with some careful wire jumping I got codes for the ECT sensor being out of range and the AIT being out of range. Also got check O2 sensor as well which makes sense since it’s missing one. I traced the sensors back to the ground and cleaned off the ground to no avail.
I’m still at a loss. Could it just outright be a bad PCM or could those sensors just both be bad and then once it gets warm it triggers the PCM to adjust for them being out of range?
Thoughts anyone?

Also can’t get the CEL to flash codes for me at all no matter which way I jumper it.

 

[ActuallyaMazda]

I have decided that tomorrow I will head to the junkyard and pull a vin X PCM and a OEM IAC from a 95 ranger 2WD at the local junkyard. I have cross referenced the part numbers between the 95 ranger 2WD and the 94 ranger 4x4 and then confirmed that they are the same for Mazda and Ford (I don’t know why they wouldn’t be, I just thought I’d make sure). I am going to check capacitors on my current one first, but if those are in decent shape, then I’ll move on to full on replacement.

 

[Josh B]

I am fairly certain you'll do best to pair your parts to a 93-94, rather than the 95.
The 93-94 models were basically a series of their own.
You are on the right track far as Mazda's being near identical those years

 

[ActuallyaMazda]

I am fairly certain you'll do best to pair your parts to a 93-94, rather than the 95.
The 93-94 models were basically a series of their own.
You are on the right track far as Mazda's being near identical those years

I’ll dig one out of a 93 instead if it’s still there. The yard I’m headed to says they got one 93 there. Thank you for the info!

 

[ActuallyaMazda]

Just pulled my PCM out. Lots of powdery white corrosion around the sides that looks like it is leaking out of the module itself but upon opening it up, the capacitors look to be alright and the rest of the computer board looks to be free of damage from corrosion or electrolytes. There is one spot along the side that looks like it has more corrosion than the rest. Unsure if this could be the issue. Pictures below. Any input on what this white stuff is, where it originates, or if this could be the issue is appreciated