P38A Sudden very high idle.

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pwood999

pwood999

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My rebuilt GEMS ran fine & sprightly to MK & back yesterday, and to Sainsbury this afternoon. For some reason when starting the car to head home today, the idle went up to 2500rpm, and then 2800. No faults logged and all fuel & air values seemed to be ok. In gear it dropped to 1100, so was able to drive home.

Re-checked all the sensor values plus throttle & cruise cables. Both have the correct slack. Finally I reset adaptive values & idle went back to normal. Will have to keep an eye on those over coming days. Not sure why it would get like that, but unfortunately those were the only values I didn't check before resetting.
 
This happened again today. Spotted the TPS Idle Reference in Nanocom had jumped to 65280 ?? Not sure why, but guessing TPS is bad, or the 5V supply has a fault.

Still no faults reported in Nanocom though.

Anyone know if the GEMS & Thor TPS are the same. Prices seem to be vastly different ?
 
Last edited:
pwood999 said:
This happened again today. Spotted the TPS Idle Reference in Nanocom had jumped to 65280 ?? Not sure why, but guessing TPS is bad, or the 5V supply has a fault.

Still no faults reported in Nanocom though.

Anyone know if the GEMS & Thor TPS are the same. Prices seem to be vastly different ?
Click to expand...
Could also be the traditional RR bad connection/corroded connector
 
I had a similar situation a few months ago on a 4L V8 - did a reset and replaced the TPS... I would just buy a second hand TPS and change it out. Be super careful removing the screws... they're very thin, and generally corroded in
 
The screws came out ok, mainly because the entire engine was stripped & cleaned, and only been used for the last few weeks. Had to order some replacement M4x25 torx because I dropped one & couldn't find it !! I suspect it went behind the exhaust heat shields & got stuck.

Looks like used TPS are around £40 on eBay. All the sellers advertising them for £10-£20 say 94-02, but never show the side where the spindle fits so impossible to see if it's the correct type. Turns out Gems & Thor use different spindle fittings. :mad:
 
Not gonna throw it. It seems to be working ok at moment after lots of contact cleaner. Resistance measures smooth on digital meter, although the flip 2k to 20k range makes it hard to tell. When it's not raining I'm planning to use my Hantek Scope to check the full 700mV to 4.5V range for stability.

Another idea I had was to pop the seal out, and see if some contact cleaner will sort the insides.

Plan-C might be to figure a way to fit a Thor sensor onto the GEMS spindle, but that's a long shot.
 
pwood999 said:
My rebuilt GEMS ran fine & sprightly to MK & back yesterday, and to Sainsbury this afternoon. For some reason when starting the car to head home today, the idle went up to 2500rpm, and then 2800. No faults logged and all fuel & air values seemed to be ok. In gear it dropped to 1100, so was able to drive home.

Re-checked all the sensor values plus throttle & cruise cables. Both have the correct slack. Finally I reset adaptive values & idle went back to normal. Will have to keep an eye on those over coming days. Not sure why it would get like that, but unfortunately those were the only values I didn't check before resetting.
Click to expand...

That Lucas computer can take up to 500 miles to get the trims sorted out after you've done a rebuild. It isn't that clever.
 
It's the TPS value jumping to 65280 that gives the problem, hence I'm assuming either bad contacts or dirty tracks. Don't mind resetting the trims if it gets me home (just not right before MOT time !! )
 
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