I am at my wits end with the IACM or stepper motor. I've had my RR for about 3 years and have done a litany of maintenance and repair work on it. The only issue I have not been able to conquer is the idle air motor.
The symptoms of my issue are hard starting and rough/searching idle as well as a CONSTANT check engine light.
I am using the Rovergauge software to access the 14cux and identify which fault codes are occurring. The only code that ever shows up is code 48.
The engine behaves like this:
- from a cold start, it takes ~5 seconds of cranking before it stumbles into a start. I say that because it isn't a clean sounding start. It sounds stumbly for the first few seconds before it revs up to ~1,800 RPM then settles back down. Cold idling isn't much of an issue.
- As the engine warms up it drives normally. Just to be clear, this issues does not affect normal driving/accelerating, only idling.
- After the engine is fully warm as determined by the Rovergauge readings for fuel and water temp, it is not until I come to a stop sign or stop light that it throws a code and the idle starts searching. It varies ~200 RPM or so, but doesn't stall. I think I have the base idle screw set a little high, which may be what is keeping it from stalling out completely.
- If I clear out the code in the Rovergauge software it comes back within 60 seconds.
First, a list of things that have been done to the engine in my ownership:
- head gaskets
- complete disassembly and cleaning of the upper intake
- New wires, cap, rotor and a brand new distributor
- MSD Digital 6A ignition control unit
- Several sets of new Champion copper OEM spec spark plugs
- New fuel and water temp sensors
- new MAF sensor
- silicone tape around the intake tube to eliminate the possibility of pinhole leaks
- New "Ford style" injectors (although I am swapping these out shortly with a different part #)
- Hedman Headers
- New waterpump and all coolant hoses
- New heavy duty cooling fan
- New fuel filter
I know some of those items are not related to this issue, but I wanted to be through.
Some of the things I have done/checked to try to fix this issue:
- Reset base idle per the Rave manual. I actually keep the allen key in the car to make adjustments from time to time.
- Set base timing, multiple times. Timing is set at ~7 deg. advanced with the procedure from the rave manual
- Tried 4 different stepper motors including OEM ones, albeit from the junkyard. I have purchased a few cross referenced ones, some as cheap as $8 or as much as $30. I have not purchased a new OEM Land Rover unit as those run in the $120 range and wont guarantee a fix. I do notice that the non-OEM ones have a slightly different cone shape than the LR ones. I'm not sure if that's causing the issue or not.
- Checked all wiring on the loom to ensure there's nothing grounded out or broken.
- Reset the stepper motor using the Rave software to ensure it is at its maximum open position when starting. Observed the activity while running using the software as well.
So, like I said, I'm at my wits end. I have put so much work into this truck and it really does drive beautifully on the highway. This idle issue is the bane of my existence at this point. If anyone has ideas of what I may have overlooked I'm all ears.