Low rpm

[Kev1976]

Hi guys
My 96 chim runs great apart from this one issue. When I’m traveling at say 70-80 mph and then drop into neutral to cruise the tick over does what it’s supposed to do. When I’m traveling at 30-40 mph and drop into neutral the tickover drops straight down to 400-500 rpm sometimes lower and occasionally has cut out. When i come to standstill it again does what it’s supposed to do and picks up to 1000rpm. Only happens at lower speeds for some reason. Cheers

[blitzracing]

The tick over is held higher when the car is rolling, but wont step down until the car comes to a stop. I suspect that the raised idle position is enough to stop the call stalling, but the idle one is not. There is a multitude of reasons for the idle to drop too rapidly such as a faulty plug, ht leads, air leak, wrong fuel mixture,or even a dirty stepper motor. The problem is the ECU software expects the idle to drop at a certain rate as it shuts the stepper motor, and when the engine slows faster than this it ends up overshooting the desired idle point that can be enough to kill the engine.

[Kev1976]

Thanks for the reply. The car has recently had a rolling road done where it was stated that on low revs the car is to rich. Could this be the issue and would you know what could be done. Cheers

[seeby]

Kev1976 said:

Hi guys
When I’m traveling at say 70-80 mph and then drop into neutral to cruise

Have I misunderstood this.Do you generally do this or just as a test to see your tickover.?Surely you wouldn't want the engine to cut out at that speed.

[Kev1976]

It’s just general driving. Slowing down on motorway I’ll just coast in neutral. It never happens doing this the car behaves perfectly. At low speed even driving around town I sometimes need to left foot brake because revs can drop to low

[citizen smith]

Kev1976 said:

It’s just general driving. Slowing down on motorway I’ll just coast in neutral. It never happens doing this the car behaves perfectly. At low speed even driving around town I sometimes need to left foot brake because revs can drop to low

Kev1976, intresting driving technique. Perhaps the cars computer can't work out the telemetry - speed to engine rev.ratio.

[blitzracing]

If the car has catalysts if should not run rich as the mixture auto adjusts, but if you get a failed lambda probe, or faulty AFM it can run rich, but the issue is the MIL light is not working so the ECU faults wont show up if the car has a faulty sensor.