View Full Version : knock sensor

11-09-2002, 03:01 PM
does the knock sensor control
idel speed and if so would a bad motor mount cause the knock sensor to retard the ignition timing,
and cause the car to idel low when in gear. not in park

or could this be a two dollar fuel filter?

11-10-2002, 04:33 AM
The EEC conrols the engine idle through the Idle Air Control (IAC) valve. This sits on the side of the throttle body and straddles the throttle plate. The EEC sends fast electrical pulses to the IAC. The problem you have is when the engine speed drops for an unknown reason, the EEC curves won't allow it to compensate for the dip properly. This is unlike a load from the A/C compressor and a load from the power steering which tell the EEC in advance.

11-10-2002, 03:50 PM
Am I the first to post the reason why bad motor mounts cause RPM drop, rough idle, and stalling?

The knock sensor picks up vibrations in a very specific range and sends a signal to the EEC, which in turn pulls out ignition timing and if the engine is at idle, it will cause the engine RPM to drop and possibly stall especially in gear.

Actually, a friend of mine discovered this and told me about it. His SC had the rough idle, interior vibration, stalling problem and could not figure out what was happening. He finally had a mechanic hook up a monitor and shift the car from park to reverse to see why the RPMs would suddenly dropped. He saw the EEC was pulling a lot of timing out for no apparent reason. They heard something knocking around and guessed a bad motor mounts were causing contact between the mount bracket and oil pan to the cross member which inturn was picked up by the knock sensor. They replaced the mounts and the problem was fixed.

11-10-2002, 09:20 PM
Yes Mez...to the best of my knowledge, you're the first.

11-10-2002, 09:31 PM
Alot of guys that use turnbuckles to hold there motor down experience the *knock * sensor problem..Specially prevelant on the grandnationals..I woudl assume it would be the same with an SC..I can imagine a bad mount coausing that