I’ve search for a few things to check, but need HELP!!

Situation: I have a stumbling idle.

First vacuum leak I found was on the fuel regulator.
Snapped that back on.

Still have a stumbling idle to almost to a die, but not quite.

Cruises fine.

I’ve cleaned the MAF and cleaned the IAT; and examined the IAC (looked ok).
Disconnected the battery for a while.
I’ve checked for other vacuum leaks and found none.

Please help

Prior to any work had these:
KOEO:54 35 43
CM: 32 75 43


After disconnecting the battery the CM’s went away but the
KOEO remain: 54 35 43
And KOER: 44 35 43

 

Since you are reporting 2 digit codes, can I assume we are talking about a '91 Explorer 4.0 V6? If so, then some of those codes don't make sense. Your profile says you have a '94 Explorer. If your working on a '94 Explorer, you should be getting 3 digit codes. Repeat the tests and make certain you are interpreting the codes correctly. Code by code analysis:

KOEO 54: IAT reading high. IAT is a simple thermister (resistance is a function of temperature). This shouldn't be too hard to diagnose. Check for bad wiring between IAT and PCM, check resistance of IAT. Chiltons (and other manuals) will have a chart that shows resistance vs. temperature.

KOEO 35: EGR sensor signal out of range. Except a '91 4.0 didn't have an EGR system. Are you certain of this code (or have I made a bad assumption about the engine model)?

KOEO 43: O2 sensor code. Normally O2 sensor isn't tested during the KOEO test. Again, are you certain of this code?

KOER 44: My code list says "AIR system inoperative" To my knowledge, the 4.0 never had an AIR injection system. Is this code correct?

KOER 35: EGR sensor code again, but, as noted, '91 4.0 didn't have an EGR system.

KOER 43: O2 sensor code. Was the engine/sensor properly preheated before performing the KOER test?

As I said, I'm assuming a '91 Explorer. If this is on your '94, you should be getting 3 digit codes (which would explain why some of the codes don't make sense). In this case, review test procedure and verify that you aren't getting 3 digit codes.

 

Thanks for your response Mrshorty (been waiting for you to chime in).

Yes it is a 94 XLT V6 144k miles.

My mistake...I thought they were 2 digit codes...I will rerun to detemine 3 digit codes.
That explains why they did not repeat twice.

(first blush) tells me
koeo:543 543
cm: 327 543

But I will confirm

 

Checking my notes...
My KOEO were 543 543
and CM 327 543

Now that my battery was disconnected I am only getting
KOEO 543 543
CM 543 543

Also, after reading about 543 fuel pump power to pcm signal, I did some probing.
I checked the green with amber tracer wire all the way back to the pcm (passenger a-piller kick panel) and I get 12 volts on it, at key on as I hear the pump running. I know this by pushing a small nail thru the back of the harness as it was hooked to the pcm and reference to ground.

What else can I look at

 

What is your fuel pressure?

 

Sorry for the delay but it's been quite hot out.
Cooled off a bit, the air and the truck engine, that I could check pressures.

Key cycle #1 about 18 psi
Key cycle #2 about 35 psi
Key cycle #3 about 40psi .. held about that for 5 min with key off.

Then I started it and got 30psi at idle...

Disconnected vacuum line to fuel regulator and jumped to 40psi at idle.

 

Does the fuel pressure stay 30-40 psi when you rev the engine (a road test might be more meaningful)? It would appear that the KOEO/CM 543 is a "false" code, because the fuel pump is obviously running. Just need to verify that the fuel pump is running consistently enough to keep up with engine demand. Also, it's possible that the computer is seeing an intermittent cutting out of the fuel pump that we can't readily see.

If the fuel pressure remains above 30 psi at all times, then lack of fuel wouldn't explain the stumble. It would be nice to resolve the 543, though.

Does the EGR code stay away?

Other causes of stumbling: dirty IAC, dirty MAF, vacuum leak, dead/weak cylinder.

 

Reving my engine (short bursts) with vacuum..it maintained 30psi.

BuT I will have to drive a HARD drive condition...never thought that it may happen then.
I will have to figure a way to route my fuel pressure gauge from under the hood so as I can view it while driving. any suggestions?
( I am starting to think that the stumble came form the vacuum line that came off my fuel pressure regulator, and some how triggered the egr code as it stumbled?)

To date the egr code is staying away. will recheck when i hook up my pressure gauge.