High idle drama 1996 D1 nanocom question/idle reference speed

Gordo

Well-known member
Hey guys, Just wanted to see if someone can help me understand what is going on with my gems 96 disco. Its been having intermittent high idle issues for a couple months. I changed the IACV with a jeep one (rotating back to the old one does the same), a used known good TPS, a new MAF, vacuum hoses, etc. I cant seem to figure it out. I have a nanocom so I have reset the adaptives and that works great but it wont stay that way. A week or less later and the high idle is back. The only thing I keep seeing wrong is a super high idle reference speed of 65280 when its mad and the IACV reacts by opening up and going crazy. When its happy the steps are around 22-24 (run line) and idle reference speed is 700ish. Im at a loss as something is going nuts here. I have also noticed the saved TPS value is off from the actual value and wrote in a correction using nanocom but it doesn't seem to stick long and the numbers are slightly off after a while. I guess that could be related. Fucking Gems trucks suck. nano.jpg
 

1of40

Well-known member
Oct 23, 2017
244
58
Va
Following. My kids revs high at start up and won’t dial down until moved into gear. Not great for engine wear.
 

boxster

Well-known member
Jun 1, 2009
443
88
Fallbrook Ca.
Following. My kids revs high at start up and won’t dial down until moved into gear. Not great for engine wear.
ECM failure maybe? Had this same problem, after lots of trouble shooting removed ECM opened and found burned up, replaced used and corrected the problem.
 

4Runner

Well-known member
May 24, 2007
660
110
Boise Idaho
At the time I had my 96 Disco, I didn’t have access to a scanner or live data so I had to just try things. I pulled the screws out of my TPS and tried rotating it slightly. Oddly enough my high idle problems went away. I turned the holes into slots and tightened it down where it was happy. Drove it for 100k that was without a problem. Not sure why it liked that and didn’t adapt to whatever the setting used to be. Couldn’t hurt to just pull the screws while it’s doing that and see what happens. Did you check the vacuum line for your fuel pressure regulator? Eventually I also checked and adjusted the base idle but never touched the TPS again.
 

p m

Administrator
Staff member
Apr 19, 2004
15,617
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La Jolla, CA
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To each his/her own - to me, GEMS is a great compromise between functionality and reliability. The only time GEMS really failed on any of my trucks was when the tone ring fell off the flywheel - can't really blame it.

Don't have time to offer you any meaningful help now - but if you haven't seen "GEMS by Poole," it is attached.
 

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Gordo

Well-known member
Thanks to both of you guys! I think I’m going to try turning the tps a little. For some reason it is still reading a bit different on actual vs stored value even after writing the correct value in the nanocom. Perhaps I reset adaptives afterwards. I know the gems is simple but this problem is associated with that high idle speed reference and I’m just not sure what’s causing it. My first gems truck. I guess it’s a learning experience. Had a few older cux14 trucks and testing with the manual and a voltmeter isn’t fun either. It’s probably something stupid.
 

p m

Administrator
Staff member
Apr 19, 2004
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La Jolla, CA
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Had a few older cux14 trucks and testing with the manual and a voltmeter isn’t fun either.
Guess what, I thought I knew most of what's there to know about 14CUX, and yet my trail Classic has a hunting idle I cannot fix without making it impossible to pass smog...
 

boxster

Well-known member
Jun 1, 2009
443
88
Fallbrook Ca.
ECM failure maybe? Had this same problem, after lots of trouble shooting removed ECM opened and found burned up, replaced used and corrected the problem.
Also had trouble with a bad IAC Valve symptom was start up, idle high then when warmed up would die out, wouldn’t hold idle rpm, replaced with new valve problem solved however had to do drive cycle around awhile to relearn idle setting.
 

boxster

Well-known member
Jun 1, 2009
443
88
Fallbrook Ca.
Also had trouble with a bad IAC Valve symptom was start up, idle high then when warmed up would die out, wouldn’t hold idle rpm, replaced with new valve problem solved however had to do drive cycle around awhile to relearn idle setting.
Might run it by “pdxrovermech” he works on Rovers Only for a living.
 

Gordo

Well-known member
Just wanted to report back. I elongated the holes in the tps and installed it back in the original spot. Still showing an idle speed reference of 65280/high idle. IACV going high etc. Rotated it slightly clockwise. Idled perfect, and reference speed at 710. Noticed the actual and saved values of closed tps now even and at .70. Reset adaptives once more. We will see if it lasts but it is great now. In my searches I found mention of 65280 idle reference speed before on auto logic and with a tps issue. And if the stored closed value of tps is less than the actual value it can cause high idle. Figured this may help someone someday.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
Make sure your throttle cable isn't holding the throttle open a little. I usually loosen the 8mm bolts that clamp the cable to the plenum. that gets bumped around or when someone has the plenum off they dont realize that will hold the throttle open and don't pay attention when they blast those back in.
 

salvvia

Well-known member
May 28, 2005
990
39
BIG WHEEL ROVN IN KNOXVEGAS TN.
where on your wire was the issue? Was it right at the plug or further up?
If i remember it was about 8-10 inches above cps I ended up replacing that last section of wire and connectors to cps its a short run
There is a connector close to the intake just strip the old loom cover off wire and follow the wires from cps up to the top of motor i hope your deal was easier than mine i had trouble finding replacement connectors i think i finnaly found them at horeillys
 

mjbrox

Well-known member
Jun 30, 2008
1,812
48
Golden CO
If i remember it was about 8-10 inches above cps I ended up replacing that last section of wire and connectors to cps its a short run
There is a connector close to the intake just strip the old loom cover off wire and follow the wires from cps up to the top of motor i hope your deal was easier than mine i had trouble finding replacement connectors i think i finnaly found them at horeillys
Okay, I had the same issue on mine. The wires had super brittle insulation. I actually stole one of the plugs from my fog lights that are not used.

Last night I pealed back the plastic and the rest of the wire looks good. I am going to buy a new sensor today and see if that is my issue.
 
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Knightspirit

Well-known member
Sep 22, 2019
251
84
Mount Shasta, CA
ECM failure maybe? Had this same problem, after lots of trouble shooting removed ECM opened and found burned up, replaced used and corrected the problem.
I have a similar problem - idle is high at start - then settles down once moving and warmed up. I saw this in the manual - does anyone have any info on resetting all of this stuff should I replace the ECM?

NOTE: After fitting a different ECM, a full tune procedure must be carried out using Testbook.
The ECM inputs and outputs are shown in the table.
 

robertf

Well-known member
Jan 22, 2006
4,778
354
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check the battery cables first. I know my 97 5 speed has a very high idle if the battery connection isnt perfect.

if you changed something and think you need to reset the adaptive values you can do it with this

 

Gordo

Well-known member
The TPS elongated holes trick worked on my high idle and it has not returned.
I did recently have issues with the cps wiring too but it was cutting out over 2500rpms with no high idle. Those wires were shot and can create all kinds of issues so I would check that as well. I have nanocom but resetting the adaptives helps with new parts
I have a spare ECM and 10as box and when I swap them in the truck will run fine. It is an advanced evap ecu on an older evap system so it does kick check engine lights but its just a spare. I was able to marry the ECU to a spare 10as box with the nanocom as I didnt have a matching set. Good luck.