As I've posted before, I have a surging idle, going from 600rpm to 900 rpm, and back and forth. I notice on my tuner's real-time data logger that the MAF sensor surges along with the RPMs, from 4.8 Gm/S to 5.4 Gm/S and back and forth.

Since the MAF doesn't do anything except measure air passing by, this means something past the MAF must be letting air past, the throttle body.

So if the TB is slightly opening and closing while sitting in idle does that mean the TB is most likely bad or something in the car is causing it to open and close?

Keep in mind I've tried unplugging the battery, sea-foaming engine, CRC MAF Clean'ing the MAF sensor, replacing air filter, cleaning TB bladesetc, nothing has worked.

Opinions please.

 

I had a similar situation. I reloaded my tune and it was ok.

 

Mine will swing from13's to 15's pretty much all the time until I get into the boost.

What if your ECU is changing the fuel? That would cause rpms surging. While warming up, mine will very exactly like you said. After it's warm it (rpms) remains consistant. The A/F bounces all over while on cruise and at idle. I asked my tuner about it and he said it was in "lambda mode" I never heard this before.

 

Interesting... I don't mind having an idle surge, its not the end of the world, even if its a bad TB. My concern is something is broke... A vacuum leak that will lead to worse things later, or a TB that will electronically freak out and slam into WOT and kill me. Who knows.

 

Highly unlikely the TB is opening and closing on its own -something is most likely commanding it to open and close (if it is in fact opening and closing). Is there a way the datalogger can display the TPS voltage (throttle position)? If not, you can tap into it directly with a volt meter. Most systems should show about 1 +/-.1VDC at idle.

In any case I would suspect some other piece of the puzzle like the tune, the ECU, sensors, or MAF. The first thing I'd look at would be the tune though. A vacuum leak will usually just make your car run like crap.

 

Well the TB could open and close because of a bad TPS sensor, right? And they're sold as one $200 piece so either way new TB. But yes, I'll look at the predator's data logger tonight for a TPS voltage reading. Thanks.