Alright, This one has me stumped (not that it takes much). Been having issues with the Disco shutting off when I cold start in the morning, a serious lag between pushing on the gas from a stop sign and engine response, and the occasional dipping RPMs at idle (doesn't stall, but seems like it wants to). Along with all new steering components & brakes parts, I had the stepper motor & TPS replaced. Well after everything was replaced, I had a high idle issue (1800-2000 RPM's) when cold, and 850-1100 when warmed up. Now if I drive about a mile or so & turn it off for a minute or so, the idle will be 900ish when started back up. In scanning the former posts, I took it to the local foreign mechanic with that "$17,000 scan tool" (heard that about 15 times from him today), who says the reason my truck is idling so high & erratically is because my ECU is reading my Air Intake Temp at -38 degrees, although my Ultra Gauge is reading pretty close to the morning ambient temp (but even that is about 5 degrees different than the engine temp before starting). He said he tested the sensor and it is fine, but with the ECU removed and tested, it still reads -38 degrees eliminating the possibility of a short in the part or the wiring. He says after several hours of testing & subsequent labor costs I need an ECU to overcome the obvious short within the ECU which would correct the idle & the -38 reading. Couldn't find anything in my search that confirms his diagnosis or offer corrective actions? Help!?!

 

I dont have much in the way of help to offer......but went thru the same exact thing with my '98......no one here locally can reprogram a Rover ecu, and I havent yet made the trip to get it done....My trouble started this winter with the same exact symptoms.....and eventually wouldnt run at all.....Tom R had found an issue with his truck....the fuel tankpressure sensor shorted out and since it gets it's power from the same circuit as the TPS and IAC..it f'd them all up.....my truck returned to almost normal by unplugging the fuel tank pressure sensor at the fuel pump connection...idle was still high after that but it ran ok, then unplugged the IAC when it was warmed up and idling about right....at a cold start you need to step on the gas just a little for a few seconds.....I still need to get it reset though.
mine only read -36 below though LOL !

 

Your ultraguage reads normal on the intake temp? If so then I call BS on his diagnostic. Did he at least reset the ECU adaptive values?

 

Isn't the fuel tank pressure switch the black box on the passenger side fender, or is that something else?

 

He said it wouldn't let him reset the adaptive values because of the -38 fault. Yep, the UG reads the outside temp pretty close to what my phone tells me the local temp (well, what the temp is about 30 miles from my house) and my IAT adjusts up as the engine warms, cools down if I leave it sit for a few hours like I think it should. I was worried about the 5ish degree difference between the engine temp & the IAT readings, but I'm sure with the way the ambient temps drop here right before day light, the engine would hold that higher temp longer than the air by the filter box, right?

 

Before a cold start, such as in the morning, the IAT and coolant temp should be nearly the same. While running IAT should be much lower.

 

That's what I'm experiencing. No idea where or why they got the -38 reading. Think I spent $164.00 in labor for nothing.

 

the black box on the fenderwell is a fuel pump relay....