Nodak1

Hey everyone,

I’m having a high idle problem and it’s slowly getting worse. I apologize if there are tons of threads on this topic, just posting because of my specific setup.

00 4.0 federal emissions, AW4, 145k miles

Here’s what I’ve done to it...

4 yrs ago - had a trusted shop replace the head. No issues at all.

3 yrs ago - 4 hole injectors, THOR intake. Idle was around 650 and smooth. All good.

1.5 yrs ago - Did the Ext Idle mod and it works perfectly. 650 idle, 1000 when switched on.

About 10 months ago - 62mm throttle body. Idle raised to about 850. I left it alone for a while.

9 months ago - replaced IAC with Standard Motor Products. No change. Left it alone over the winter.

2 weeks ago - started hearing a sort of train whistle noise which changes pitch depending on rpm. Also idle is now around 1000. Somehow I think I answered my own question here.

I should add, when I stop at a store and come back out (5 min or so), it starts up and sometimes the idle drops to around 850. Then I drive it and the idle jumps back up to 1000 when I park.

I have not done an ECU reset after any of these upgrades, as I figured it would learn on its own.

So, should I go after a vacuum leak on the intake? Reset ECU? Or are there other tricks or steps to take first?

Thanks in advance.

Nodak1

I also covered the IAC passage and there was no change in idle... Normal at operating temp?

Nodak1

So the engine bogs down when carb cleaner is sprayed on the intake at the gasket. Might be hard to hear.

Think I found the problem? Should I start by replacing the Intake/exhaust gasket?

I also blew smoke into the intake via brake booster hose and it came out both front and rear either gasket or injectors... was tough to tell which one.

cruiser54

Engine cold. Snug up the intake manifold bolts in this order.

Nodak1

Thanks cruiser54!

I will give that a shot. Hope that’s all it is.

Still have some running around to do today, but I’ll report back.

Saudade

Yep, sounds like an intake leak. After you torque the manifold, recheck the TB too.

Roler

Like the diagnostic process and mentioning the recent works done, OP
better than : high idle,HELP!!!
Covering the IAC inlet at idle in your case might not make that big of a difference when engine warm and having the leaks, explaining the no differenece you found.

Nodak1

So I got a ratchet on all the bolts in order. All were tight except I got the slightest turn on #3 and #8. They popped and scared the crap out of me, thought I broke them.

Still idles at 1000 and the whistle is still there, although it seems slightly quieter... could just be me though.

used a stethoscope on the intake and that’s for sure where it’s coming from, seems louder by the ports.

Also, it idles at 750 with the A/C on. Turn it off and goes back to 1000.

Cummins93

Cover the throttle body with your hand using your palm to regulate how much air can make it into the engine. You can lower your idle down by doing this. The vac leak should become easier to detect.

Nodak1

Guys thanks for the tips, they have helped a lot!

Just tried this. Had it completely blocked it actually idled nice and low, not struggling to stay running, which REALLY surprised me.

Anyway, I could hear a hiss from near the manifold, front and back. Still couldn’t tell if it was the gasket or the injector o-rings. I twisted all the injectors but the hiss didn’t change. Whistle is still there as well when you rev it.

So...
- Manifold bolts are tight.
- TB and gasket is good (sprayed all around it with no change in idle)

Thinking it’s the gasket, injector o-rings, or even both? I sprayed by the #1 injector and it bogged down slightly, like spraying the gasket only not as bad... but they are so close, could’ve been overspray going into the gasket area.

Maybe one started last year causing the 850 idle and the other one just now causing the 1k idle?

Please tell me if I’m over-complicating this LOL

agreen

Yes. Get a manifold gasket and injector Oring kit and replace them. It sounds like the manifold gasket that your shop used when they did the head gasket is probably a cheap paper one. They'll burn up over time because it's the same gasket for the intake as it is the exhaust.

Nodak1

Yeah, just have to find the time now... getting really busy at work. Those were my last days off for a month or so.

Thanks again!

Nodak1

So, last week it threw a check engine light with a P1294 code. No time to work on it and my DD, I just bit the bullet and took it to the shop.

Turned out to be only the Injector o-rings. They did a proper smoke test before and after replacing and didn’t see anything from the intake/exhaust gasket after.

Now idling at 700 in neutral, 650 in gear. Good to go.