Still sputter on decel, AAAGGHHHHHH!!!!! Options

[Nemo914]

OK, I have posted before on help with a sputter (or light "backfire") on deceleration with my 1972 1.7. It happens at around 2-3k RPM and is worse when loaded on decel. Sounds like "phfft, phfft, phfft".

Most of you suspected an exhaust leak, and in agreement, I replaced the heat exchangers with SS, with new copper seals and the works. The stock muffler is also new. It all seems solid as a rock, and I don't think it could still be leaking.

In George Hussey's "tech tips" (I know, everyone's favorite dude) it says, "If your 914 "pops" or backfires when suddenly backing off the throttle, suspect..."

1. Leaking muffler or heat exchanger to head connection
2. Fuel pressure too high
3. Throttle switch bad

But, I have had it tuned by a reputable shop, fuel pressure checked, and installed a new throttle switch. Even tried different octane gas.

It is a completely stock FI 1.7. It starts, idles and runs perfectly, except for this!! It is embarassing to drive as people admire the car and then laugh as it sputters and coughs on decel (IMG:style_emoticons/default/headbang.gif)

Does anyone have any other ideas?? I have driven this car since I was 16 (21 years to date) and it never did this until about a year ago. Any help would be appreciated.

Here are a few phots just because we all like pictures: