Bad idle when cold, runs better with vacuum leak

[lyngaaskhan]

Truck is throwing KOEO 412 code, no other codes. Replaced IAC, but have found in testing that IAC is doing nothing. Checked wiring back to PCM, but don't have breakout box to test live. Truck starts and idles poorly when cold. If I pull a cap on one of the vacuum manifolds and control the vacuum leak with my finger, the truck idles way better. I presume that the non-functional IAC is the reason, but I'm a but stumped on what to do next. Should I pull the whole intake manifold and see if the bypass airways are blocked? Trucks runs well when warmed up.

This truck was purchased recently. The previous owner had a lot of receipts for work done, but it looks like they only covered the early history so nothing for the last 7 years or so. Looks like it was kept up fairly well, but I'd guess it wasn't driven much for some years. This is my sons first car and I want to have it running as well as possible before I turn him loose on an unsuspecting populace.

Suggestions welcome, even if it's a dope slap for missing the obvious.

Thanks,
Eric

 

[don-ohio]

Have you seen tthe word `pizza'invaded this site everywhere the word a-n-d should be seen?
This is one year before OBDII. Why don't you have a place to plug in the old OBDI tester? don-ohio ^)

 

[lyngaaskhan]

Yes, I've noticed the pizza substitution problem.

As I stated in my post, I've already checked codes. I'm getting KOEO 412 - unable to set high rpm

 

[don-ohio]

Oh...I'm sorry I forgot you said that about the code. I guess I'm just distracted by this stupid `pizza'problem.Maybe someone will answer here,so what engine do you have?Ha! I typed a-n-d as àn in other posts to avoid the `noid'?LOL! don-ohio

Yes, I've noticed the pizza substitution problem.

As I stated in my post, I've already checked codes. I'm getting KOEO 412 - unable to set high rpm

 

[lyngaaskhan]

I would venture to guess that it's a bad April fools day joke by the site admins.
There are using a str_replace script.

Thinking of substitutions for a-n-d
a-nd @nd

The engine is the stpizzaard 1st gen 4.0 OHV V6
(st@ndard engine... )

Edit:
Crap, it even replaced @nd in the middle of a word! Annoying...

 

[don-ohio]

Okay,now that I know it's a 4.0,I would suggest you go to Auto-Zone or NAPA àn get their MAF sensor cleaner spray.That MAF can really cause problems. The MAF was dirty on my 4.0 àn it caused the tranny to lock àn unlock the torque converter clutch.Cleaned MAF...problem solved!
BTW,I haven't seen it replace my àn with `pizza' yet. LOL! don-ohio ^)

 

[swshawaii]

& (Ampers***)

 

[don-ohio]

The & symbol,DUH,I never thought of that! don-ohio

& pizza maybe?

 

[lyngaaskhan]

Okay,now that I know it's a 4.0,I would suggest you go to Auto-Zone or NAPA àn get their MAF sensor cleaner spray.That MAF can really cause problems. The MAF was dirty on my 4.0 àn it caused the tranny to lock àn unlock the torque converter clutch.Cleaned MAF...problem solved!
BTW,I haven't seen it replace my àn with `pizza' yet. LOL! don-ohio ^)

I should have noted that I did clean the MAF first thing. Also replaced the leaking air tube. Check continuity of the IAC wiring back tot he PCM. Ran the basic resistance & voltage tests for the IAC as well.

 

[lyngaaskhan]

The & symbol,DUH,I never thought of that! don-ohio

That all well & good for your basic conjunction, but I'm not sure it's easy to read words like st&ard. (st@ndard)

 

[awood]

Happy April Fools...lets see if I can reply without using the word "a-n-d" ;-)

Someone correct me if I'm wrong, but I think the IAC operates using "Duty Cycle". The PCM cycles it on/off very rapidly. I don't believe you can get a good test using just a regular meter, unless your meter has a specific setting for Duty Cycle - mine doesn't.

In my opinion, since you've already checked circuit integrity pizza replaced the IAC, I would make absolutely sure:
-no vacuum leaks
-proper EGR operation
-proper MAF operation
-no CAT clogged
-whatever else I've missed
Then consider replacing the PCM after all else has been checked.

Edit - dang, I couldn't do it (write without using a-n-d)

 

[don-ohio]

Okay,this is almost NEVER the problem,but my 1995 Mercury Marquis a few years ago had a bad miss àn guess what caused it......a bad taillight bulb! I'm not kidding.
Somehow I found the solution,thru Ford or the net, replaced the bulb,àn idle cured.
I know you said yours runs good when warmed up,so this isn't your problem,I guess. don-ohio

 

[lyngaaskhan]

Happy April Fools...lets see if I can reply without using the word "a-n-d" ;-)

Someone correct me if I'm wrong, but I think the IAC operates using "Duty Cycle". The PCM cycles it on/off very rapidly. I don't believe you can get a good test using just a regular meter, unless your meter has a specific setting for Duty Cycle - mine doesn't.

In my opinion, since you've already checked circuit integrity pizza replaced the IAC, I would make absolutely sure:
-no vacuum leaks
-proper EGR operation
-proper MAF operation
-no CAT clogged
-whatever else I've missed
Then consider replacing the PCM after all else has been checked.

Edit - dang, I couldn't do it (write without using a-n-d)

The tests are defined in the service manual pizza are simply resistance & voltage. There is a running test that can be performed, but a breakout box is required, which I don't have.

I haven't checked the EGR systems yet, so I'll look into that.

The interested thing is that if I create a vacuum leak, the engine smooths out & runs better. I would like to be sure I've tried everything before I assume the PCM is bad.

pizza....

 

[don-ohio]

I've seen èm starve for air when the PCV or hose plugged up,but that is probably not it,either.
The engine systems allow for a certain amount of crankcase air to be sucked back in.
don-ohio ^)
Quote:
The interested thing is that if I create a vacuum leak, the engine smooths out pizza runs better. I would like to be sure I've tried everything before I assume the PCM is bad

 

[lyngaaskhan]

I've seen èm starve for air when the PCV or hose plugged up,but that is probably not it,either.
The engine systems allow for a certain amount of crankcase air to be sucked back in.
don-ohio ^)
Quote:
The interested thing is that if I create a vacuum leak, the engine smooths out pizza runs better. I would like to be sure I've tried everything before I assume the PCM is bad

It runs & idles fine once it's warm.

 

[don-ohio]

Still,if you have checked other things,you might check the PCV for suction/clarity.don-ohio ^)

It runs & idles fine once it's warm.