High Idle, high RPM in neutral while at speed
 

So this past week I cleaned my throttle body, nothing complicated, disconnected connector, removed 4 bolts, cleaned with carb choke cleaner, was careful not to over actuate the throttle plate, also replace air filter... re-installed and torqued...
Throttle Body Bolts
89 lb in
Throttle Body Nuts
89 lb in
After it was all together an out for a test drive I have noticed that the idle speed is higher by about 400 rpm and when I am at highway speeds and I shift to neutral, the RPM surges to, and stays at 2000 rpm....
I have not follow up with a battery disconnect yet, as I want to see if its just a learning curve the will be completed with several drive cycles...
I also noticed that when coasting I use to get 99 MPG in V4, but now only get about 67 MPG in V4... again because of the higher idle...
(The spec does say to not to reuse the gasket again, though I saw nothing wrong with it, and left it in place)

Vacuum leak. With it idling take some starting fluid and spray around the base of the throttle body. It will rev up if its a small leak but if its a big enough leak it will actually idle down. I have tried reusing the throttle body gaskets before and it always comes back to bite me. Every time I've ended up with a vacuum leak. Hope this helps

I think you are right... I got to thinking about it last night and was coming to that conclusion....I'll check it out this evening:o

I've had good luck using O2 safe RTV and wiping most of it off, leaving a very thin layer so squeeze out is minimized to re-use a gasket.

Mine did the same after cleaning the throttle body. It corrected itself after a few hours of driving. The battery disconnect may also work.

I did the propane leak test and there was no rise in RPM, so no leak but I did replace the gasket with OEM but no change. Did the battery disconnect and no change...I will give it a few drive cycles...

Double check the MAF sensor connections and that the MAF itself did not get any dirt or debris contamination since everything was disturbed.

May also want to lubricate the butterfly with WD40 since carb cleaner is very harsh and is not specific to be used as Throttle body cleaner.

Since you say no vacuum leak is present something is probably simply amiss.

The ECU will not "Learn" while cycling if something physical is not rite.It will only "learn" short term fuel trims...such as crappy gas etc.

I did inspect the MAF and used canned air to blow it out when I did the original TB cleaning...

The throttle plate felt pretty smooth and I was frugal with the cleaner, but I will re-evaluate. I believe it is designed to operate "dry" adding something oily may cause it to collect particulate debris and bind.

I'll do some reading up in the manual this week, it does seem to be calming down..

Perhaps a chunk of crud got jostled or washed down the idle air control passage (that opening in front of the butterfly), stuck to the IAC plunger, causing it to not seat completely.

Throttle Learn
 

AhHa! reading is fundamental:D...

Attached to the throttle body cleaning is...Throttle Learn :cool:


2007 Chevrolet Tahoe - 2WD | Avalanche, Escalade, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 1820246
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Throttle Learn
Description
The engine control module (ECM) learns the idle position of the throttle plate to ensure the correct idle. Anytime the throttle body is cleaned or replaced, the ECM must learn the new throttle position. The idle may be unstable or a DTC may set if the throttle position is not learned.

Conditions for Running the Throttle Learn Procedure
• DTCs P0101, P0102, P0103, P0107, P0108, P0111, P0112, P0113, P0506, and P0507 are not set.

• The engine speed is between 450-4,000 RPM.

• The manifold absolute pressure (MAP) is greater than 5 kPa.

• The mass air flow (MAF) is greater than 2 g/s.

• The ignition 1 voltage is greater than 10 volts.

Throttle Learn
Important: Do NOT perform this procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Start and idle the engine in PARK for 3 minutes.
With a scan tool, monitor desired and actual RPM.
The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
Ignition OFF for 60 seconds.
Start and idle the engine in PARK for 3 minutes.
After the 3 minute run time the engine should be idling normal.
Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.

⇒ If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

After the drive cycle, the engine should be idling normally.
⇒ If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.

Once the engine speed has returned to normal, clear DTCs.