Bad MAF or Throttle Body?

[Whamhammer]

Hi all,

I am noticing a problem that has gotten worse, since I had the 6.0L swap.

While rolling in neutral (25 mph and up), the WS6's idle starts increasing from the normal ~1k-ish up to past 2k - 2.5k RPM, tapping the gas doesn't bring it down; if I push in the clutch, the RPM drops to standard idle again. The guy who did the engine build and tuning drove the car all the way up from Southern VA, past Baltimore to me, so I figure that if it was a tune issue he would have noticed it driving over 300 miles to me.

I am also noticing that rolling from a start/idle isn't as smooth isn't as one would think it should be (stop and go is a nightmare) and sometimes it has a "hiccup" at part throttle a moment before I am ready to start and upshift.

Gas milage keeps staying crappy, the best that I have had is 17 MPG with highway driving and I just experienced 10 MPG just driving around my suburban town, not driving hard or anything (the interior is even removed except the driver's seat for the moment).

I replaced both the IAC, TPS, and air filter, in the fall. I haven't had a code pop up, and none are showing when I had plugged in the code scanner. It even passed emissions testing's plug-in.

Any ideas? MAF sensor? Throttle Body? Something else that I am not thinking of?

[SMWS6TA]

I wish I got 17mph.

I'm also Speed Denisty tuned.


Are there any changes to the rear gear ratio?
if auto did, you change the stall to deal with the new engine. iirc the cam profile affects the torque curve, and that will also affect mpg as well.

[Whamhammer]

I wish I got 17mph.

I'm also Speed Denisty tuned.


Are there any changes to the rear gear ratio?
if auto did, you change the stall to deal with the new engine. iirc the cam profile affects the torque curve, and that will also affect mpg as well.

It's a stock 6-speed & rear end, so it's a 3.42 axle ratio.

The cam is either 224 or 228 duration Texas Speed bumpstick, so it's not a radical camshaft.

Its feeling like a drivability issue more than a powerband issue to me, I would figure with the bump from 5.7L to 6.0L, the low-end torque would still be equivalent, even with a peakier torque band.

[SMWS6TA]

Are you going off the cluster for the rpms? mine is about 300-400 off. I even verified it with a code reader that gives me live data and it matches my aftermarket tach and Raptor shift light.

if you can use a code reader that provides live data I would check it first.

Next go over every vacuum hose as well as checking the map sensor on the back of the intake. is intake stock or aftermarket like a FAST? I ask because when I was trying to tune mine after rebuild we were chasing the idle all over.. once above 2k it settled down and ran great. idle like shit. Turned out to be 2 things. map sensor was cracked and the seal on the back of the FAST intake was bad. Fix both and my tune got finished.

[Whamhammer]

Are you going off the cluster for the rpms? mine is about 300-400 off. I even verified it with a code reader that gives me live data and it matches my aftermarket tach and Raptor shift light.

if you can use a code reader that provides live data I would check it first.

Next go over every vacuum hose as well as checking the map sensor on the back of the intake. is intake stock or aftermarket like a FAST? I ask because when I was trying to tune mine after rebuild we were chasing the idle all over.. once above 2k it settled down and ran great. idle like shit. Turned out to be 2 things. map sensor was cracked and the seal on the back of the FAST intake was bad. Fix both and my tune got finished.

I am going off the cluster, my ears, and car vibration, the revs certainly double-up; and it only happens under those certain circumstances.

The intake is the factory LS6 intake manifold.

As far as vacuum... '02s don't have EGR, the secondary air setup is deleted (I did put a plug on the SLP air lid for the hole), the PCV lines are brand new, OEM lines, and I have an Elite Engineering PCV air catch can, which is properly routed. I've sprayed carb cleaner around the hoses and didn't get anything.

Can't think of any other vacuum lines.

[SMWS6TA]

hvac and brake booster are located on the back of the intake.

Check the catch can hoses.