I have a 1999 Discovery SD with 4.0 GEMS and 124k miles. When I start the engine from cold, it idles at 3,000 rpm or so. If I feather the accelerator pedal I can get the rpm to go down just a bit. After 3 or 4 minutes, I shut off the motor, turn it back on, and it idles at 750. The TPS shows 637 in both situations, the MAF shows 0.3 at the 3k idle, and 0 at the warm idle. I have a spare 98 Disco that I swapped the IAVC with, and have the same issue. I picked up a IACV at a junkyard and have the same issue. I cleaned both of them before I tried them. The TPS values change as I depress the accelerator. I've cleaned the MAF with the CRC MAF cleaner. I even tried the MAF from the other Discovery with the same results. The MAFs are both SAGEM, one shows a build date of 1998, the other 2006. Both give the same results. I'm guessing the 0.3 reading at 3k rpm idle on cold startup is a result of the increased airflow. I've tried 2 different IACV parts and would think it odd that 2 would be bad. Any ideas on what I need to look at?

 

Having the adaptive values reset.

Requires either a trip to the dealer or an independent shop with the right diagnostic system.

By the way, you don't want to let a Rover idle past 2500 in park, you'll eventually toast it's auto tranny. 3k is asking for it sooner than later.

 

I tried a GEMS reset at my brother in law's shop, but could not get the scan tools to connect. He has a Launch X431 and an Autel DS708. Neither would connect, but his Snap-On OBDII scanner as well as my Actron would connect. I did do a CEL reset after I changed the IACV and cleaned the MAF - I had a P1178 code. Is it possible that the scan tools won't connect until a drive cycle is complete? Or do I have a wacko ECU?

 

Well unless they have purchased a plug in Land Rover code is encrypted. Neither OBD-II scan tool can touch it, all you get is the generic "P" codes and can reset the CEL and that's it. Autologic, Black Box, Rovacom are the three outside venders that can reset "adaptive" values. Testbook T3/T4 is what the dealers use(d). Your ECU is fine, doing what it's designed to.

Original O2's perhaps? 124k is 24k over the max life expectancy. This is in reference to the P1178 which means it's either the O2's (my guess) or a genuine real lean condition such as fuel filter, injector, pump, vacuum as a lean source.

 

Update - When I changed the valve cover gasket I missed a vacuum hose that connects to a round device on driver's side of the fuel rail. I didn't use the copper spray on the gasket when I out it in the first time and it started leaking around the driver side water port. I put in a new gasket and used copper spray on the bottom and gray silicone on the top. The idle returned to normal for about a week. Now it will start at 1500 and as it warms up will settle at 750 to 800 once warm. The CEL has not come on since I did the reset about a month ago. I also adjusted the throttle cable as it had a little slack in it.