revs when lifting off accelerator pedal
 

2007 Pontiac Grand Prix NA 3.8

as the title says, the engine revs when lifting off accelerator pedal as I drive. is this a common issue? is there a common place where a vacuum leak forms on this engine?

incidentally, it does have a code for the downstream O2 sensor, but i assumed that isn't something that would affect the air fuel mixture in this way, or was GM so uptight about emissions and fuel efficiency that they lean out your ratio if the post cat sensor doesn't pickup any O2?

Does it seem like it almost wants to stall out before it starts catching itself with the revving?

well, it doesn't feel like it pulls quite as hard as before this problem showed up, but i wouldn't say it wants to stall.

No other codes listed?

there were a bunch that blew when i had the passenger seat disconnected for a day while swapping it out, but they haven't come back since reconnect and reset.

the O2 code was a P0036 - HO2S Heater Control Circuit Bank 1 Sensor 2

You could try and spray brake clean around the top of the engine while its running to check for vacuum leaks, but aside from that, its hard to say what is causing this without some sort of hard fault, or live data from a good scanner.

I have a Bluedriver and it has live data. what should I be looking at?

How much does it rev?

. . . like you're driving along at 2,000RPM and you let your foot off the pedal and it goes to . . .

. . . 2,100RPM?
. . . 2,008RPM?
. . . 5,000RPM?

No, the PCM reverts to pre-mapped values so as to put a good effort into saving your catalytic converter from damage but not do such a good job of conserving fuel and maximizing emissions reductions.

ok, i tried that with spray carb cleaner and detected no change in RPM.

It happens when i'm cruising, like 2500RPM or so if I recall. The engine will feel a little bogged down if I'm accelerating very mildly and it will sound bogged down as well, then when I let up it will blip up like 250-500 RPM if I recall. If I accelerate harder, it punches through the bogging down, pulls solid, and then the tac comes down steady afterward without the blip up.


hmm.