Detecting Swipes is Unreliable - Help Please

[DenVog]

I am trying to detect a two finger vertical swipe, and then take an action. Specifically I want to fade an image in, or out, depending on its current state. I can get it to work, but it is very unreliable. Sometimes it will work a few times in a row. Other times I might swipe 10 times before it works, even though I'm making the same motion (length, speed, area on screen).

User Interaction and Multiple Touch are both enable for the items in Interface Builder. My related controller.h code

// swipes
#define kMinimumGestureLength	25
#define kMaximumVariance		5

typedef enum  {
	kNoSwipe = 0
	,kHorizontalSwipe 
	,kVerticalSwipe
} SwipeType;

@interface LifeForceViewController : UIViewController <UIAccelerometerDelegate, UIActionSheetDelegate> {
	//swipes
	CGPoint	gestureStartPoint;
}

//swipes
@property CGPoint gestureStartPoint;

my related controller.m code

//swipes
@synthesize gestureStartPoint;
// swipes
#pragma mark -
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
	UITouch *touch = [touches anyObject];
	gestureStartPoint = [touch locationInView:self.view];
}

// swipes
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
	UITouch *touch = [touches anyObject];
		CGPoint currentPosition = [touch locationInView:self.view];
		CGFloat deltaX = fabsf(gestureStartPoint.x - currentPosition.x);
		CGFloat deltaY = fabsf(gestureStartPoint.y - currentPosition.y);
/* commented out because detecting vertical swipe only
	if (deltaX >= kMinimumGestureLength && deltaY <= kMaximumVariance) {
			// handle horizontal swipe
		
	}	
	else  */
	if (deltaY >= kMinimumGestureLength && deltaX <= kMaximumVariance) {
		// handle vertical swipe
	 if ([touches count] == 2)
		{
			if (imageView.alpha == 0)
// method to fade in image
				[self imageIn];
		}
	 else
		{	
// method to fade out image
			[self imageOut];
		} 
	}
}

I have been through the forum, and the source code from the Beginning iPhone Development Book, but am not finding a way to resolve this. Any insight is appreciated.

PS-I had a touchesEnded event that is used to switch from my info view back to the main screen. I thought maybe it was interfering, but commented it out and no change.