For those that don't want to crunch paragraphs worth of data, here's the short story...
Why is my car faster with the check engine light on? I have a 2009 Toyota Avalon XL.
Now, for those hardcore data lovers like myself, here's the gory details...
In September 2012 I ran a 15.108 @ 92.82 mph. It was 90 degrees out. I had a K&N cai, deleted 3rd cat and resonator and Dynomax mufflers. I was on the stock 16 inch alloy wheels and 215-60-R16 tires. Also, My CEL was on at the time.
Since then, I've installed the MKC y-pipe, replace all of the exhaust after that with 2.5 inch piping, switched to Borla Pro XS mufflers, got a throttle body spacer and a Jet performance maf sensor. I "upgraded" the wheels and tires to 18 inch Enkei J10's and 225-40-R18 Continental Extreme Contact DW and lowered the car with "Ebay" springs. Also I added the rear wing from a dodge charger(looks amazing!).
After all of that, on May 22nd this year I ran a 15.050 @ 93 mph. It was 78 degrees out and my CEL was on.
Of course, I was expecting a faster time after adding so many "mods", so I scoured the internet looking for validations for my mods, or the reason why my time was virtually unchanged. Well, hard evidence supporting or dismissing throttle body spacers and the Jet maf sensor proved to be super elusive, so I just decided to take a page out of Myxalplyx's book and answer my questions on the track with a good ol' fashioned test n' tune. The wing was the first thing to go...
Here's the times I ran today. The temp outside was 89 degrees.
No Jet maf, no spacer, CEL ON...
14.604 secs @ 96.04 mph
14.725 secs @ 95.91 mph
14.770 secs @95.64 mph
No Jet maf, no spacer, CEL OFF...
14.984 secs @ 94.80 mph
15.021 secs @ 94.14 mph
15.111 secs @ 94.87 mph
Installed Jet Maf, no spacer , CEL ON...
14.808 secs @ 95.61 mph
15.035 secs @ 95.10 mph
15.039 secs @ 94.52 mph
No Jet Maf, installed Spacer, CEL ON...
14.784 secs @ 95.84 mph
14.826 secs @ 94.86 mph
14.886 secs @ 95.17 mph
Great day at the track today! Looks like I gained half a sec with lighter wheels and tires and the performance y-pipe. As you can see, the Jet Maf not only didn't make me faster, it appears that it was slowing me down. I was honestly surprised, because my "butt dyno" was telling me the complete opposite. The throttle body spacer was also a slight bottleneck. I imaging its because its slowing air down at higher RPMs. the most baffling thing is the check engine light. Why is the car so much slower when everything is supposed to be working correctly?