Intermittent high idle and whining sound

[JIMMYRIG]

I'm getting high idles and a whirring/whining sound (maybe vacuum leak) plus bad throttle response. It used to just happen after freeway driving, now its as soon as the truck is warm and gets worse after driving. Idles at like 2k sometimes after sustained freeway driving. I've chased all the vacuum lines and sprayed with brake clean, I had a thought it could be brake booster, maybe IAC (although its new and made no difference unplugged), or cracked intake/bad manifold gasket. Any ideas?

[hgeranium]

5 hours ago, JIMMYRIG said:

I'm getting high idles and a whirring/whining sound (maybe vacuum leak) plus bad throttle response. It used to just happen after freeway driving, now its as soon as the truck is warm and gets worse after driving. Idles at like 2k sometimes after sustained freeway driving. I've chased all the vacuum lines and sprayed with brake clean, I had a thought it could be brake booster, maybe IAC (although its new and made no difference unplugged), or cracked intake/bad manifold gasket. Any ideas?

I've had bad IACs out of the box. 2/3 of the new ones I've bought have been like that. Manifold gasket could always be a culprit. If you haven't tried, tighten the bolts. What do you have? 2.5? 4.0? Renix or HO? Your course of action can change based on this.

 

Is your EGR hooked up or plugged correctly? I had a similar high idle issue and something that seems to have helped fix it was a new EGR gasket. Mine was totally toast.

 

If you have a renix, the MAP to TB vacuum line is especially important. Cruiser54 has a tip to improve it.

 

Also worth checking your throttle body gasket and also making sure the throttle plate isn't getting physically stuck by debris. I would take the TB off, clean it, and replace the gasket. Especially clean the IAC port.

 

Just a few starting points, I'm sure others will have much more to say. Good luck!

[JIMMYRIG]

Its a 4.0 Renix. The EGR could be bad. The truck does not pass smog - numbers point EGR or CAT. So maybe that's the culprit. How would I confirm if the EGR is functioning? I also will note I haven't been able to recreate when letting the truck warm up and idle/rev when stationary. It's only when driving which is why I'm also thinking brake booster. Does that track?

[hgeranium]

42 minutes ago, JIMMYRIG said:

Its a 4.0 Renix. The EGR could be bad. The truck does not pass smog - numbers point EGR or CAT. So maybe that's the culprit. How would I confirm if the EGR is functioning? I also will note I haven't been able to recreate when letting the truck warm up and idle/rev when stationary. It's only when driving which is why I'm also thinking brake booster. Does that track?

If it was the brake booster, then you’d typically see it when you press on the brake. The brakes would be very soft or not work at all; you’ll know for sure if it was at the booster. 
 

There’s a cruiser54 tip for checking exhaust restriction here
 

You could try to bypass the EGR to see if it runs better. All you need to do is cap off the lines at the EGR valve, air box (if you still have the original one; my renix has an HO box without the vacuum ports) and the vac fitting on the intake manifold. I have a c shaped hose connecting the two ports but you can also just cap those off individually. If it runs better than you can go about fixing up the EGR/replacing the cat to pass emissions. 

[JIMMYRIG]

Sounds good, you've been very informative. Thank you. I'll cap the EGR and see how it runs. I do get a little bit of a whine when I press and release the pedal. It's not quite the same volume or tone and doesn't affect idle but could that be a sign of a bad booster too?

[JIMMYRIG]

Also Ill confirm its a picknpull booster from a 97+

[hgeranium]

1 hour ago, JIMMYRIG said:

Sounds good, you've been very informative. Thank you. I'll cap the EGR and see how it runs. I do get a little bit of a whine when I press and release the pedal. It's not quite the same volume or tone and doesn't affect idle but could that be a sign of a bad booster too?

All good on brake fluid?? If it’s making a noise then there’s definitely something off but if it doesn’t affect engine performance then you’re most likely good on vacuum. If you have a second person, you can get them to pump the brakes with the truck on and hit all around the vacuum port and around the booster itself with brake cleaner to make sure it’s not leaking.

 

The difference between a 97+ and pre-97 booster is out of my wheelhouse so hopefully someone else chimes in on if there would be any problems retrofitting (assuming it’s not the exact same part). 
 

However, the fact that the issue seems to be exacerbated by heat leads me to argue that the exhaust manifold bolts or gasket are a likely contributor.  It makes sense that heat expansion on the manifold surface and gasket could create an intermittent leak if the gasket isn’t all the way sealed. I have the same issue. Starts and idles great on cold starts but I frequently have trouble after it warms up. 

[JIMMYRIG]

As far as I know the dual diaphragm swap is common, it was doing good for a while but as of late I've been noticing that noise when depress the pedal. I can't say for sure if that's related to my vacuum whine and high idle (which is definitely affecting performance). There's no vacuum leak to the line going to the booster. I'll also probly just go ahead and replace the manifold gasket, it couldn't hurt.

[Eagle_SX4]

Isolate the booster as the source of the leak. Pull the vacuum line off the intake manifold and plug it. See if your symptoms go away. 

 

I would do this only after the engine is showing the symptoms. Your brake pedal will be much harder to use so DRIVE WITH CAUTION. 

[JIMMYRIG]

Ok I'll try that. I was messing around and found out if I pump the pedal quickly I can get idle to rise which I would assume wouldn't happen with any vacuum leak

[JIMMYRIG]

So just pulled the booster line while it was idling high and plugged it - no difference. I’ll look into manifold next

[hgeranium]

9 hours ago, JIMMYRIG said:

So just pulled the booster line while it was idling high and plugged it - no difference. I’ll look into manifold next

IIRC you can use a spray bottle of water which will lower the idle instead of raise it when checking around the manifold.  That may be a little safer (and cheaper) using on a hot engine compared to brake cleaner. 
 

those bottom manifold bolts are a pain. I’ve been told that you can get them from the top by removing the airbox but it’s not worth fumbling blindly. I just take the airbox off and get them from under the truck. You’ve got plenty of room. Also make sure you actually have all the bolts. I’ve heard of people who were missing bolts or studs entirely. 

[hgeranium]

 

[AnotherOldJeepGuy]

Nice Picture 

The ones I originally put in the "?" were from my first look and seeing bolts at those locations but not hole in the manifold to match.  I later decided the bolts at those locations the bolt/washer just tighten on the tabs on the manifolds, just didn't bother taking out the "?".

[hgeranium]

26 minutes ago, AnotherOldJeepGuy said:

Nice Picture 

The ones I originally put in the "?" were from my first look and seeing bolts at those locations but not hole in the manifold to match.  I later decided the bolts at those locations the bolt/washer just tighten on the tabs on the manifolds, just didn't bother taking out the "?".

Your immaculate drawing will surely stand the test of time as a guide for all things manifold bolts