Rev drops slowly from 1500 RPM after complete stop

[ToniCipriani]

Not sure when exactly did this started happening, but I noticed my car would stick at 1500RPM (sometimes 1800RPM - 2000RPM) after coming to a complete stop and thrown into neutral. After being stuck for a few seconds, it'll slowly drop back to the usual level.

Checked floormats and pedals already, not stuck at all.

Only recent happenings are installing my GMPP intake, replaced cat and water pump under warranty, and battery went flat and jumpstarted after I came back from vacation. Could the jumpstart of the battery messed up a sensor or something, or the cat failed again?

[glake89]

Sticking throttle actuator or pedal sender?

[ToniCipriani]

Well not sure yet. I'm booked in to the dealer for coming Fiday, just thinking if there's anything else I can check. I'm actually thinking if I should even take out my intake... dealers love to blame this and that.

[WintR]

That's normal for mine - it's an emissions thing.

[ToniCipriani]

Originally Posted by WintR That's normal for mine - it's an emissions thing.

Stuck at 2000RPM? doesn't sound right...

[Carbon Sky]

The first thing I'd do is see if there are any DTCs stored.

[ToniCipriani]

No CEL, but I'll scan it tonight anyways.

[ToniCipriani]

One more finding... It only happens after the car is fully warmed, above 91 degrees Celsius.

[ToniCipriani]

Partially fixed. My intake was loose after the MAF, so part of it was disconnected. I've reseated it now, and seems to have cured it, except that now it still does it a tad bit about 1000RPM but it drops revs much more normal now. Probably because of the loose intake it was running lean for a bit, the computer needs to relearn?

I hope I didn't do any damage... gonna get an oil change ASAP to get whatever crap it sucked in this period out (due for one anyways).

[WintR]

Originally Posted by ToniCipriani Stuck at 2000RPM? doesn't sound right...

If I take it out of gear while moving, or as soon as stopped, it hangs above idle a few seconds. The computer holds the throttle open a bit while the car is moving, to minimize emissions when you take your foot off the pedal. It takes a second or two for it to drop all the way to closed-throttle idle.
Leaking air around the MAF will confuse the computer, though, making it hold the throttle open more, because it doesn't know about the extra air flow. Now you've corrected that problem, it will hunt for the new setting a while.

[ToniCipriani]

Makes sense. I'll continue to monitor it for a few days. Thanks!

[ToniCipriani]

Update... still does 2K, but only on rare occasions where I am stuck in traffic. What worries me is that it actually rev itself up to that much.

I wonder if the battery jump really did mess up the PCM and I should do a battery disconnect.

[ToniCipriani]

Just tried scanning, no codes. Couldn't try a battery pull, socket won't reach the neg terminal.

Gonna give it another try for another week to see if the blipping goes away.

[TomatoSoup]

Originally Posted by ToniCipriani Just tried scanning, no codes. Couldn't try a battery pull, socket won't reach the neg terminal. Gonna give it another try for another week to see if the blipping goes away.

You can easily disconnect the battery at the underhood fuse box (under the red cap). You don't have to pull the actual battery cable.

Or easier still, if just resetting codes, pull the ECM fuses How To Remove The Ecu .

[tincharriot]

Originally Posted by ToniCipriani Update... still does 2K, but only on rare occasions where I am stuck in traffic. What worries me is that it actually rev itself up to that much. I wonder if the battery jump really did mess up the PCM and I should do a battery disconnect.

One area to look at is the throttle shaft, one end has the actuator and bushing, the other end has a sealed bearing with a small end cap like a freeze plug. Any resistance in the bearing can cause the throttle from closing fully when the throttle pedal is released, thus causing a slow drop in RPM after the throttle pedal is released just enough where the ECM cannot detect a code from the throttle actuator.

Remove the throttle assy from the intake manifold. Slowly open the throttle blade and release it watching it close, see how far the blade closes should close completely without any resistance, if there is any slight resistance in the throttle blade from closing all the way there is a good possibility that the bearing is dried out of grease and possibly corroded from moisture.
You can drill a small 1/8 in. hole in the plug and add some type of lubricant to the bearing and seal it with a dab of silicone.

I had the same situation before and in time has progressively worsened to the point my car went into limp mode.
I dismantled the Old assembly for investigation and found that the bearing was 50% corroded out.

Hope this helps.