Odd stalling/sputtering after long deceleration

My car has been running great since the TFi was replaced but I've had an odd issue prior and since..

If I'm going say 70mph down the highway and I push the clutch in, the revs drop down to 1000 and settle in around 900 or so just like you would expect..

BUT, If I down shift to 4th from 70mph and go down a long (1/2 mile) exit ramp with the car engine breaking the whole way as I get to the stop sign and push the clutch in, the revs drop to 400 and stumble all over the place trying to keep the car going and the 'running rich' smell is overpowering.

It's only after a long decel that this issue comes up.. Every other instance of disengaging the clutch results in a normal smooth idle.

Ideas?

Just guessing but check the IAC connector

FPR diaphram starting to leak?? If the diaphram is starting to leak, the long period of high vacuum during the long decel may be sucking some gas into the motor thru the vac line to the FPR, causing overly rich condition. If it stays rich for more than 15 sec at idle when it should be in closed loop, you should have a CM code 42 stored. If the FPR is of unknown age / origin, it might make sense to replace it for peace of mind, as the FPRs are a fairly common failure.

Thanks guys, I'll look into those things..

I've still got a Walbro and Kirban sitting here.. Might be a good time for some preventative maintenence. I'm 99.9% certain the FPR is stock from 86. I'll also take a close look at the wiring harness at the IAC. I have had that area apart for cleaning in the last 6 months..

Kev, pull the vac line off the FPR and see if there is any gas or strong gas smell in the line. If there is, FPR is starting to leak. I had one once that actually shot gas out of the bung on the FPR, which made the motor run really bad at idle and light cruise, but still ran good at WOT. As long as you have a Kirban already, throw it on and see if it solves the problem.

Jeff,
Very interesting observation. I'm getting a KOER code 42 not CM. KOEO and CM are code 11. So far everything is checking out okay per the service code tests. And I'm getting a haze out the exhaust at idle, so maybe.... I'll check it tomorrow. I have a used spare so I may just throw that on.

I'll post my results.