Thread: 1996 P38A 4.0 SE RR Idle problems (GEMS)

Hi All,

I finally had time to play around with my "black box solutions" MSV system over the weekend (at this time the RR was running perfectly, I might add . In my enthusiasm I reset the "Adaptive Settings" in the GEMS ECU...thinking that was just trends based on previous drivers and tow loads etc.... and all was well (at that time). When we tried to use the vehicle on Sunday it kept stalling when it came to a slow or stop....e.g. traffic lights, corners, uturns etc.....the revs just dropped down to zero, and the engine died, although it idled ok when in park...there was no issue in starting it every time. Luckily I saved all the settings, before I reset them, however I have noticed that the "Long term idle" seems to be a value the GEMS ECU has to learn over time, and the original value of 39 cannot be written back to the ECU. In the interim, to get the base idle up, I put a turn or so on the accelerator cable...to get the idle in "D" to about 750 RPM....took it for a quick 15 min drive last night with the laptop and MSV connected and capturing data.....the "long term Idle is now at 10, from 0 (but was originally 39 before the reset)", and was able to undo some of my adjustment on the accelerator cable to get the correct idle. I know that the accelerator cable should only be adjusted to just engage the throttle, so I am wondering if this reset has highlighted some other problem with the throttle position sensor, MAF, or Idle Air Control Valve (EL Stepper motor). I've checked all air/vac hoses, there does not appear to be any cracks, or splits. I cleaned the MAF (Gently) about 3 months ago, and it is still as clean as a whistle, the air filter element is about 1 month old...the RR starts better than our new Chrysler 300C (every time)....so I'm confused as to why the ECU cannot compensate to keep the idle up to the correct level, unless it is not getting a correct signal from a sensor. I thought that the adaptive settings would automatically compensate to correct the current operating conditions of the vehicle. I've checked the Becm, Gearbox, Gems, EAS...there are no errors on any of them. I know that there are different default ECU values, based on temperature....when the RR was stalling ambient was around 8 Deg C. Hope that gives enough information. I would appreciate any advice, or suggestions.

On another note I'd also like to caution anyone about changing any settings on their otherwise good RR.....a simple setting can make all the difference!! ...bottom line (as the old saying goes)....if it's working leave it alone

Thanks,

Brucep

Problem Solved.

After taking the vehicle on a 1200km trip it still needed the extra turns on the accelerator cable linkage to maintain idle when at a stop....intermittently. It seemed to depend on which temperature map the ECU was using at the time as to whether the idle was 700, 1100, or 300 RPM.
Today I decided to check all the sensors and hoses again...all seemed OK, so as a last resort I removed the Idle Air Control Valve (EL Stepper motor)....it was all gunked up with crusty black oil residue....I cleaned the manifold, and the plunger / tapered valve of the idle motor and put everything back together. The vehicle now has idle feedback, so when the revs drop the ECU automatically adjusts, and stabilises at the correct RPM level. Was able to return the accelerator cable linkage back to it's original position. I guess now the ECU has a value to learn against the sensor values.

Despite the initial stress of the problem I caused by resetting the adaptive values, the whole experience has given me a better understanding of the complex engine management system (I think I've read just about every LR forum, LR publication, and Morgan GEMS reference that I could find).....the ECU has basically compensated for the build up of gunk in the idle motor over time, and kept the vehicle running very well....until I reset the values, and it did not have the benefit of learning them over time !

I think that long term, solving this issue now has saved some problems in the future, and I am actually glad this happened.....I've learnt alot, and the vehicle is also better off by having a working idle motor.

Hope this might be of help to someone else.

Regards,

Brucep