06 Solstice. Again.

I have an intermittent check engine light. I hooked up the laptop to the car this morning and found:

  • 0171 - System Too Lean (Bank 1) (Immature)
  • P0507 - Idle Air Control System RPM Higher Than Expected (History) (Immature)
  • P0833 - Clutch Pedal Switch B Circuit (Immature)
  • P0507 - Idle Air Control System RPM Higher Than Expected

The P0833 is a new one. I'm not sure exactly what would make a clutch pedal switch "immature."

Other symptoms:

Potential vacuum leak: I can hear a steady hissing sound near the intake manifold, but it's not clear where it is coming from. Other than an occasional rough start - starts fine but stumbles and hunts for a few seconds - I don't see any indication of a vacuum leak. My boost gauge registers -20PSI vacuum at idle, which is about where it's always been.

Note that the intake manifold on this engine (Ecotec 2.4L LE5, inline 4 cylinder) has o-rings in the manifold, and doesn't use a gasket. A quick check with a ratchet indicates that it's tight, and I don't see any obvious broken or loose hoses. Still, probably worth investigating further.

I appear to need a new valve cover gasket - seeing some oil around the edges.

Last weekend, the car got pretty hot (~235F) at an autocross. I noticed some coolant smoke/steam coming from near the turbo and cat, but it's inconsistent and very slight. It's been suggested that, when I replace the valve cover gasket, I make sure that the head bolts are torqued correctly as they could have loosened up when the engine got hot.

Possibly related: I ran a compression check and found (from front of engine) 120, 120, 140, 140. Spec for this engine is closer to 150, but it's running fine.

When idling, the temp will climb from ~190F to ~203F and go back down. Doesn't really happen when driving. Water pump and thermostat were replaced a few weeks ago along with the engine.

Oh yeah - it's a "new" engine. It's possible something was overlooked during the install. (Shop installed the engine, not me this time.)

Suggestions? Please ask if I've omitted any crucial information.

Also, it idles high (around 1500 RPM) most of the time. After sitting at a light for awhile it will sometimes drop back to 1000 or so.

  • 2
    Immature could be an odd translation of Intermittent, or a code that is new and hasn't been repeated.
    – JPhi1618
    Oct 20, 2015 at 17:21
  • @JPhi1618 : Maybe premature?
    – Zaid
    Oct 20, 2015 at 18:25
  • David, you mention a boost gauge, but I don't think the Ecotec LE5 is turbocharged. Could you clarify?
    – Zaid
    Oct 20, 2015 at 18:30
  • @Zaid aftermarket turbo.
    – 3Dave
    Oct 20, 2015 at 18:30
  • Oh wow, that changes a lot of things...
    – Zaid
    Oct 20, 2015 at 18:34

1 Answer 1

  • P0171 - System Too Lean (Bank 1) (Immature)
  • P0507 - Idle Air Control System RPM Higher Than Expected (History) (Immature)
  • Potential vacuum leak: I can hear a steady hissing sound near the intake manifold
  • Also, it idles high (around 1500 RPM) most of the time.

All of the above are symptoms of unmetered air making it's way into the cylinders. The fact that you have an aftermarket turbo probably aggravated the situation and caused the lean code to appear.

I suspect that the leak should be somewhere after the MAF/MAP sensor and before the turbo. A quick and easy way to locate the area where the intake is leaking is to spray carb cleaner or introduce propane around the intake plumbing.If sprayed near the leaking area you should be able to hear engine RPM change.

  • Thanks - I'll give it a shot. Although, both the MAP and MAF are after the turbo and inter cooler. :/
    – 3Dave
    Oct 20, 2015 at 20:35
  • @DavidLively : Then in that case I expect the leak to be after the MAF/MAP.
    – Zaid
    Oct 21, 2015 at 13:47
  • Also, this car appears to have a MAP AND a MAF. (I know the MAP is there as I installed a 2 bar unit). The MAP is near the intake manifold and fuel rail. The MAF is in the intake tube about 2 feet before the throttle body. I thought MAP and MAF were mutually exclusive. :/
    – 3Dave
    Oct 21, 2015 at 13:57
  • @DavidLively : They are separate sensors. The reason I say that the leak is after the sensors is because the cylinders are seeing more air than what the sensors have detected. Come to think of it, the leak could be anywhere after the MAF. In most intake setups with both MAF and MAP the MAF is responsible for measuring air flow; MAP is used for other secondary functions under normal operation.
    – Zaid
    Oct 21, 2015 at 13:59
  • That makes sense. Otherwise the leak would just be an additional, unfiltered intake path.
    – 3Dave
    Oct 21, 2015 at 14:00

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