Light-weight Flywheel Issue

Authored/Compiled by: Bill Gregory (sansho@rennlist.com) 

and Jon Kaminsky (jon@rennlist.com)

Date: August 9, 2002
Lightweight flywheels, by their nature, weigh less than the stock flywheels, and allow the engine to rev quicker...as result of less rotational moment to overcome.  However, they also allow the revs to drop quicker, and the 964 DME software can't keep up with the rapid drop, often resulting in a stalled engine.

 Some third party DME chip modifiers attempt to get around this by tricking the DME into thinking that the air conditioner is on. An alternative is to use a semi-lightweight flywheel, possibly with modified DME software. Andial in California is known to take this approach with some success.

Reportedly, there is also a "remapped idle stabilization valve" available that is claimed to address this issue.  This issue was discussed on a couple Rennlist threads here: "Idle Stabilization Valve Adjustable" and here: "ISV for 964 with LWF."

Adrian Streather adds:

"Every 964 has an idle speed control valve which is set by the DME so I guess you could call it software controlled and programmed related. The 964RS used a different flywheel sensor and timing ring with its lightweight flywheel and lightweight clutch and a different remapped DME."
Jeff Curtis notes that:

"The idle stabilization unit is adjusted permanently, is installed by the factory in your 964, and resides near the throttle body. The "modified" idle stabilization units have the housing drilled out and tapped for an adjustment screw. This basically allows you to bump up your idle a bit to reduce, or in most cases, eliminate the stalling caused by a LWF."