So, after doing a bit of cleaning up yesterday (airboxes, filters, throttle body, plug wire greasing/tightening), I fired up Missy to take her for a test drive and see if I unleashed a few extra horses. Well, when I hit the gas to rev her up and she stayed at 3k RPMs - had to shut her off manually because the revs kept slowly climbing - I knew I screwed the pooch on something.

Come this morning, I found that infamous little vacuum hose underneath the driver's side airbox had gotten unplugged and figured that might have been the culprit... nope. Idle is pretty smooth now, albeit a bit high (1.1-1.3k on a cold start), but whenever I hit the gas pedal, even just a quick tap, the revs jump to 2.5-3k and stay there. The throttle body plate (?) moves freely and cleanly, and I sprayed it down with TB cleaner again like I did yesterday when it was off the car (I covered the plug for the wiring harness that goes into it), but could manually having moved the butterfly screwed anything up? When I had it off yesterday, I just sprayed TB cleaner on quad-folded shop towels and wiped out the grime/oil that was in there. Was that a bad move?

Also, where the two vacuum hoses come together into one and come into the small hole on the bottom of the TB, I found this -



That small tube inside the vacuum hose looked like that yesterday when I took the TB off so I assumed that nothing was wrong with it, as I didn't have any problems before taking it off, but now I have to wonder if that's what is causing this issue.

Also, bonus points - what's the narrow wiring harness that plugs into the TB? Is that the TPS?

I guess it's just a drainage tube to the heads for any oil buildup in the TB. Problem still exists after clearing a P0120 (Throttle Position Sensor/Circuit A), but after driving the **** out of it for 20 minutes, it didn't come back so hopefully, cleaning the TB wiring harness and getting some silicone grease on there will help fix this.

that hose looks like it gets connected to your intake Y-Tube

That's what I thought at first, but there's no connector on the Y-splitter for it yet there is one on the TB assembly that *should* fit perfectly. I just couldn't figure out why there was a tube within the hose itself, but who knows? It's not the cause of this crazy idle surging, and that's how it was when I took off the TB, so why worry?

That tube is there, just to make a better seal, use some RTV on that connection. Have you adapted the throttle after cleaning? Hope you did not unscrew the plate.

Yeah, I did the throttle reset and when the engine isn't jerking around in revs, it's running extremely smoothly compared to before. I only sprayed the heck out of the throttle body with TB cleaner and manually moved the butterfly to get the grime out from around its edges. Would that screw anything up?

The car is perfectly driveable - 5.4s 0-60 and 13.8 quarter mile with the engine very heated up in 90+ outside temps - and the mileage is phenomenal compared to before the cleaning, so I know it's would assume it's not any sensor or the plugs getting fouled up. The idle is still way high (1.2-1.5k RPM) to the point where I have to really apply the brakes at stoplights, but it's only in neutral or park when the engine revs itself all the way up to 3k+ RPMs and then keeps slowly rising that gives me serious concern.

Vacuum leak 100%

That's what I was thinking too, but I checked all the hoses I could find and they all seem to be in good condition. If I get a vacuum gauge and check the pressure via the little hose on top of the supercharger/intake plenum, what values should I be looking for?

How many miles has it been since you cleaned your tb?

I disassembled my tb when I replaced my intercooler and gave it a through cleaning. The first 10-15 miles after I did it, the rpm was acting up exactly like you described.

After that, everything was okay though, I suspect the tb cleaner might have something to do with it.

I had never even looked at previously, truth be told. It wasn't very dirty or grimy at all, compared to some pics I've seen on here. And I didn't take it apart at all; I just took it off, covered the wiring connector, and sprayed the schmutz off the butterfly and housing.

Was it doing the "nudge the gas and rocket the RPMs to 3K" thing as well? The jumping/surging RPMs at idle in drive/reverse seems like an software, wiring or vacuum thing, but I haven't a clue about the neutral/park thing with the engine racing by itself.

I had that problem when the wiring harness that connects to the top of tb was not attached properly and or dirty. Try cleaning the harness with electronic cleaner and ziptie the connection.

Just got back from AutoZone with some cleaner. Wish me luck =)

Try this to stop the surging, turn the key to position two for one minute. If you pop the hood, you should hear the TB whirring and resetting itself.

Then start the car and see if the idle surging has stopped.

Hmm, I always wondered what that whirring was. It's worth a shot - digging through EPC for the specific section of wiring harness that goes to the TB is making my brain hurt.

Well, it got my initial idle back down to normal, and it got rid of the crazy "rev to 3k+ with a tiny stab of throttle" issue, so I definitely owe you for that. Still has the surging (1.4k->1.7k->1.4k->1.7kl) at idle after any throttle is applied, but hey, at least it's progress

I did ask you if made a throttle adaptation))) and you said yes...
Now find the leak.

My mechanic thinks it doesn't make any difference, but I used to unplug the TB for one minute with no key in ignition. Plug the TB back in, then put in the key, turn to position two, wait one minute, then start.

You could try this too and see if it makes anymore difference??

I think I've read that on the forums here before as making a difference too, so I'll definitely try it =)

I don't think manually moving the butterfly on an electronic drive-by-wire system is a good idea.
Was the throttle body removed when you did this?

I hope it isn't, but that could be the source of your issue.

Yeah, I didn't think of that when I was cleaning it. I'll confess to being a dumb Polack sometimes

I think that's what caused the crazy high revving, but the little TB auto-calibration procedure got rid of those. Now to finally source out the problem causing the weird idle surges...

I've been having this same rev surge for about a year now. I've tried the #2 key position and pressing the gas pedal for about 10 secs. I've also cleaned the outer edge (just before the valve) of the inside diamenter of the TB.
I find the rev surges on gear at a stop and if you don't hold down on the brakes, you could get into trouble. Engine revs pretty high during morning starts and afternoon starts, too, but comes down to normal eventually. I've just learned how to live with it.

60n, Try GrammaBenz's solution above for forcing the TB to do a manual reset. It brought my standing idle back down to nOrmal and made driving in traffic a lot easier. What you're doing sounds like resetting the throttle adaptations in the ECU.

Love the whole Vader look on your car, btw =)

Hey Doug,

Try what I mentioned earlier. Take out your key, Pop the hood, pull the connector off the Throttle body.
Wait one minute.
Plug it back in, turn the key to position two, then wait another minute.
Start car....

See if this does the trick for you.

Good luck!