help with rough idle

[Todd Staples]

I pulled my engine to replace seals and gaskets and clean it up. I have had injectors cleaned and tuned, new distributor and rotor, plugs and wires, new vacumm lines, fuel filter. I am certain the balance shafts and timing belts are set correctly. I have a rough idle which smooths out when you increase the trottle. Anyone have any suggestions on what to check? I bought this car in Vegas and drove it home 1300 miles and it got over 30 mpg and ran pretty smooth but did have a vibration at startup which was probably because of motor mounts which I also replaced. Could it be the idle control valve?
Thanks,
Todd

[SoCal Driver]

Could have the balance shafts out of alignment. Imporperly set idle speed can cause this. The later 944's have a test plug on the driver side fender close to the firewall. To set the idle pins B and C have to be connected.

[olerebel]

I have the same problem with a rough idle. The car seems to drive fine but bounces between 750 - 950 rpm when at idle. Can you elaborate more on this test plug?

[SoCal Driver]

Round plug with snap cover mounted to the fender seam inside the engine compartment just in front of the fire wall on the driver side.

Reason for jumping the two contacts is it cancels out the DME from trying to reset the idle as you try to adjust it. The idle "hunting" you describe can be attributed to not jumping the pins when the idle was set.

Also check the clamps and fitting of the large rubber J boot between the AFS and the throttle body. As the rubber ages it hardens and loosens on the two flanges. Check the fittings for the large vacuum line that runs to the brake booster and other places.