Thread: Idling Fast

Hi All

I have just completed a major rebuild on my 1997 3.9 V8i Discovery 1 and so far it is running very well and actually has some fuel economy again.

I purchased a fully reconditioned long motor and installed the following new parts

Alternator
Distributor
IAC stepper motor
All hoses
Injectors
Throttle Position sensor
Fuel temp sensor
Water temp sensor (for fuel injection)
Water temp sensor for guage

I fitted the plenum that came with the reconditioned engine simply because it was a lot cleaner than my old one.

The MAF was cleaned and tested on another discovery and confirmed to be working fine.

The engine started first time when installed and the only thing I noticed was the engine was idling fast, about 1300rpm on the tacho on the dashboard.

I noticed about 30 seconds after starting the idle had dropped to just under 1000rpm, again on the tacho on the dashboard. In Drive or Reverse the idle was indicating about 750rpm.

I set the timing at 2 degrees BTDC with the vacuum advance hose disconnected and blocked. To get the idle speed down to 750 I put the car in drive as it was still indicating just under 1000 in neutral.

Every time the car is started cold the idle is up near 1300 for up to 20 seconds where it falls to just under 1000. When hot the idle is 1300 for a second or 2 before falling to just under 1000.

The car drives great with plenty of power and when I took it for a long run on the weekend the fuel economy was much better than I had ever experienced in the 4 years I have had the car.

I am just concerned about the idle speed. Although the tacho is indicating a fast idle the car does not feel like it is idling fast when in drive or reverse. I am trying to borrow a decent tacho to find out what the real idle speed is.

Can anyone explain why I am getting the fast idle at start that drops down to just under 1000rpm indicated. Is it likely that my idle speed is in fact correct but the tacho is now over reading? If so how can I get the idle speed to indicate correctly.

Regards

Richard

Rickl
Not sure if I have anything to add of value but something I have noticed with mine is if I have disconnected the battery the idle will be higher than usual on start up after reconnecting it.I can see no reason for this but it has happened on a number of occassions (also when the battery went flat from leaving the interior light on ).
The idle returns to normal as it should a few seconds after startup and the higher than normal initial revs go away after a few days.
Anyone else noticed this?