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So, long story short is my car is currently stumping both myself and my crazy Z friend who literally built his TT out of parts in laundry bins. Tried almost everything we can think of, so looking for input. Symptoms are that it idles lean, like really lean (wideband reads 17.2 with spikes "off the charts at 20+), and crappily, cold or hot same idle. It sounds like a systemic intermittent miss due to the mix being too lean to reliably combust. The trick is that as soon as you give it the least throttle it runs beautifully and the wideband reads perfectly between 14.4 and 14.7 as long as the throttle is open. The car is a TT with a freshly rebuilt motor and new transmission. Things we checked:
Spark is good on all 6
Compression is between 160 and 165 on all 6.
Capping and eliminating the Air Regulator did nothing whatsoever.
IACV seems to be working fine, and is about 14 months old. Able to set base idle just fine.
TPS is .4v with the hard idle on
Tested MAF with a known good, it's fine.
Engine vacuum is a steady 18 to 20 at idle.
Looked for vac leaks all over, found none.
Timing is square at 15
I swear it looks like a bad a** a vac leak, we just can't find one anywhere. Any other "out of the box" ideas? Thanks!
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