High and hanging idle - 5.3

[OneOffStroker]

I had to have my new-to-me 5.3 rebuilt because of bad cam bearings that resulted in little to no oil pressure.

Now that it's rebuilt, I started it up and I have great oil pressure now, but the idle does not go below 1000, and when I rev it a little bit, it hangs for 5-10 seconds before going back down to 1000. It did not act like this originally, and I'm not sure if there may be some kind of tuning/relearn issue, or did I just mess up something on my install.

It did not do this before the rebuild. The intake gaskets were replaced during my original install, but have been on/off a few times, but have only a few actual minutes of run-time on them. I have another new set of intake gaskets and throttle body gaskets from the rebuild that I may put on, but wanted to get some ideas first about if it could be tune related?

[BR3W CITY]

Unless your tuner set your idle that high, I'd doubt it was tune related.

How long have you let it idle? When mine starts cold idle is like 980 for 20 seconds, then come down to high 8xx until settling out at 820's. It takes about 2 minutes from cold to drop down, and then it also drops into the high 7s when put into gear and loaded up.

As for the hanging; an intake side leak on the manifold or tb could get a little extra air in there and cause a high idle. Does the pedal/tb seem to work fine when you rev it? TPS sensors can cause weird idles and hanging/bouncing throttle issues, but might throw a code. Check the wires from the TB and give them a little tug, they should stay firm but sometimes are prone to breaking/bending/or having the pin or wire pull out. Its an easy fix if its the issue.

[whitels1]

I had a similar issue with mine, ended up I ran my PCV incorrectly(1 vacuum leak) and 1 port on the intake was not plugged(2nd vacuum leak). I would look for vacuum leaks, if you have tuning software or have a tuner he should be able to spot what is going on easily. Also check your throttle position at idle.

[OneOffStroker]

Well, I don't think the idle is set high, because it was installed and running fine (around 800RPM) before I had it rebuilt. The throttle response was dead on and it didn't hang before either. I have checked all the vacuum ports, and they go where they need to or are appropriately plugged. This is also a DBW motor, so throttle position doesn't really change like cable TBs do.
I will just have to find/make time this week to remove and clean the throttle body and intake and set new gaskets in as well. After that, I'll either be good or back to square one...
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[BR3W CITY]

Originally Posted by OneOffStroker

This is also a DBW motor, so throttle position doesn't really change like cable TBs do.
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Whether or not it operates like a cable TB isn't really germane. The wires are a known problem on many IIrc dbw pedals operate either on a single rheostat reading (0-10v input) or 2 rheostats reading 0-10v and 10-0v as a doublecheck on the newer pedals. I'd think that on a 0-10v sensor, if a sensor read 6.5v instead of 10v at WOT, you'd have a problem. I'm not saying its the problem, but you can't completely discount the DBW, its not a foolproof system.

[OneOffStroker]

Well, turns out I'm an idiot. When I was doing something on the install, most likely messing with the oil pressure stuff on the back of the block, I knocked off the vacuum cap on the rear of the manifold. I don't run a vacuum booster because I have Hydroboost, so this was easy enough to overlook. What I find weird is that it doesn't make any noise when it's uncapped, unlike the one on the top of the intake.

Well, I have a new cap that is siliconed on there, so I shouldn't have this problem again.

Thanks for the tips.

[BR3W CITY]

Its always the simple stuff isn't it.