Slow idle when engine hot

[MGVWfan]

What I found was a combination of adding 220 Ohms of resistance in series with the CHT, and adjusting the fuel pressure up to 32 PSI eliminated the tendency to die at idle in hot weather (and corrected other mixture-related funnies at the same time). It's probably the corn squeezins and other nasty oygenates in our modern US-spec fuel that causes such heartburn for the T4 and D-Jet. As I've discovered recently with the Eberspaecher fuel pump vapor locking woes, "modern" Houston-spec (and probably US-spec) fuel will bubble and foam at the least provocation, causing grief for the Eber in the return line, and maybe it's doing something similar in the pressurized part of the FI system at normal system pressure?

I could never get the idle limiter to behave right , so I removed it, no real problems without it.

Also, on the decel valve, my '73 412 variant with AT sold in Houston, TX (US Federal Spec, therefore) did not have a decel valve. One might postulate that a PO removed it, but the AT pressure switch that goes along with the AT version of the decel valve was not present on the AT, and there was no evidence of a non-factory (or recently-installed) plug at the port used by the decel valve switch, and no provision in the wiring harness for the line from the switch to the valve, so I can safely assume my car came from the factory without it. I'm betting some got it, some didn't. MoPar was the same way in the 70's, some emission-related features were phased-in over a model run, some got it, some didn't. Makes for fun and games trying to figure out what carb you have on your /6 (for example).

[btectonic]

I've had major troubles with this lately and am curious to know how much a fried automatic trans would effect the idle speed/stability.

All things being equal, every vacuum and air leak has been hunted down and eliminated, pcv valve eliminated for Ray's fixed orifice (4mm) mod, leaky dashpot disconnected, retard line disconnected, and so on. The only thing I haven't done is re-braze the vacuum fittings on the plenum to insure there's no leaks there. F.I.'s solid.

The idle throbs. Doesn't motor boat like it would if the f.i. was faulty. Acceleration's not at all what it should be with a rebuilt engine (8.5:1 w/1.8 dished pistons); you can definitely feel it when the torque convertor locks up at stall speed, car grabs the road, around 35m.p.h in 2nd, around 60m.p.h in 3rd.

Pulled the original D code convertor replaced it with a fresh K. Something bad happened there, within 150 miles after the swap and a 50 mile stint on the freeway the car would die once it was hotted up. Swapped it out with a Z and things are so-so for now.



BTW: if anybody's got a core 003 they'd like to let go of give me a holler.