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Discussion Starter #1
Hello,
I have a 1992 Range Rover classic that I purchased about 4 years ago. I let it sit for over a year and had to drain the fuel tank, replace the fuel filter and fuel pump in January. The truck starts and idles fine, runs good for about 10 minutes then it starts dropping engine rpm all the way down to almost stalling. Sometimes I cant get it over 30 mph. At first I thought it was a vacuum leak so replaced all vacuum lines under the hood, the problem persisted. After a little more trying to get it to run the coolant light came on and I found a leak around the thermostat. Is there a 'safety' on the computer that will cause the engine rpm drop if it detects over heating or low coolant? I was told the problem could be the idle air control valve, does that sound like it could cause the issue?
Also the service engine light came on but I cant locate the OBD plug, any idea where that is?

Any help will be greatly appreciated.

Cheers
 

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1970-1995 Range Rover Classic
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There is no OBD2 plug on RRCs, not even the 95. ISTR, to reset the check engine light, just disconnect the battery for a few minutes. Before you do that, there is a error display under the front passenger seat. Check this before disconnecting.

Idle air a.k.a., stepper, could be a problem. It’s pretty simple to access and clean. It could also be the TPS or a few other things. Check the RAVE for the diagnostics, it will save you time and headaches to follow the RAVE processes.

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Discussion Starter #3
Thanks for the info. I checked the rrobdd unit under the passenger seat and thru code 17, which seems to be the throttle potentiometer. I reset the unit as per the instructions in the stickied article in this forum. The article says after reset it will display any other codes or be blank, but mine just kept showing up 17. I performed the reset 3 times, each time it just showed 17. So hopefully that's the only issue. That part ain't cheap...lol
 

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I used this new TPS module in my range rover classic. More reliable than the stock or used ones.

 

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I used this new TPS module in my range rover classic. More reliable than the stock or used ones.

Getting the new as opposed to used
With these newer types looks to be a very good option...
But first....try unplugging the tps ...
Clean the contacts and give it a try...
It can’t hurt... and clean the plenum....
I try most everything first ...
 

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Doesn't sound like TPS issues. Try unplugging the TPS. You should get an instant fix if that is the problem although, running it like that for any length of time will then cause it to go into a sort of limp mode. Sounds more like a stepper motor issue or maybe even O2 sensor. What's the plug colour like? Is there a heavy smell fuel?
 

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Discussion Starter #7
when I was turning the ignition forward to look at the on board diagnostic system I could hear the tps 'cycling' even with out the engine running. there is no smell of fuel with the engine running. the limp mode is what I was thinking in my initial post. is there a limp mode that will turn on for a few seconds then go back to normal from coolant temp or level? my catalytic converter does rattle, so maybe the 02? but the rrobdd only showed code 17
 

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Code 17 is defo the TPS. Just had exactly the same with mine - sourced a known good TPS and all is now well. IIRC The stepper only controls idle but you say can't get over 30mph sometimes. I doubt lambdas as the signal from these is ignored above a certain speed.
Would be well worth getting hold of RoverGuage software and lead. a Good TPS should show a gentle rise and between say 10 and 90% with throttle movement. My dead one went from 8 to 99 instantly. Also remove TPS and twist the spindle with your finger you may feel a dead spot.

 

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1970-1995 Range Rover Classic
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Code 17 is defo the TPS. Just had exactly the same with mine - sourced a known good TPS and all is now well. IIRC The stepper only controls idle but you say can't get over 30mph sometimes. I doubt lambdas as the signal from these is ignored above a certain speed.
Would be well worth getting hold of RoverGuage software and lead. a Good TPS should show a gentle rise and between say 10 and 90% with throttle movement. My dead one went from 8 to 99 instantly. Also remove TPS and twist the spindle with your finger you may feel a dead spot.

Rovergauge showed mine at over 90%, even though it was only idling. Swapped the TPS from my running parts truck, then everything was back to normal.


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The 3.5 flapper TPS have curved holds to allow for adjustment. I have one of those on my 3.9 and the ability to fine adjust was very useful. Worth setting base idle and checking timing all as one project too after a new TPS.
 

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Discussion Starter #11
Got the tps and iacv ordered, should be here in about a week. I will let yall know how it turns out. Pray for me...hehe!

Thanks for all the help!
 

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For appraisal purposes it's worth separation of some function to allow a clearer picture.

Your original description of good starting followed by restricted running has a reasonable fingerprint of a non-functioning temperature sender. It starts cold at increased fuelling, then doesn't recognise the warming engine so ecu still seeing it as cold. Would sound and smell rich and likely cap the rpm too as described. Worth checking the resistance to see what output you have.

IACV valve is only air bleed past the throttle plate to let ecu control tickover rpm. It wouldn't usually cap the rpm as it will have little influence under wider throttle opening use. It's just modulation of small amount of air with throttle plate closed.
In field "guerilla" test for IACV, with vehicle off, turn ignition on but don't start ( this should prompt IACV to open) turn off again then remove loom plug from IACV. This should leave IACV open with no control from ecu, now start it and it should go up to 2/3000 rpm as the ecu cannot close the valve to control additional air. Now switch off, reconnect IACV and start it again, control should be back in range now and prove the hardware is working.

TPS, old type with slots, you have to move it to give baseline report to ecu hence the slots. Later systems the ecu asked for report from TPS and then used that as it's baseline during ecu boot as far as I know. So in effect you can't set it as it "calibrates" each start time and makes the slots redundant.
If you just unplug the TPS and run it without, it should just pick up air volume from MAF then use just that data with default map to run competently, but without response it gets on throttle opening abruptness. If it improves with TPS unplugged it suggests there's a fault there.

I'd guide against setting base idle speed until you have it debugged, it needs to have everything working to properly set it else you can just "transfer" another fault to be included in that calibration routine, it rarely needs setting unless someone has moved it in the vain hope that it's going to improve something, that often happens though.
 

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Discussion Starter #13
For appraisal purposes it's worth separation of some function to allow a clearer picture.

Your original description of good starting followed by restricted running has a reasonable fingerprint of a non-functioning temperature sender. It starts cold at increased fuelling, then doesn't recognise the warming engine so ecu still seeing it as cold. Would sound and smell rich and likely cap the rpm too as described. Worth checking the resistance to see what output you have.

IACV valve is only air bleed past the throttle plate to let ecu control tickover rpm. It wouldn't usually cap the rpm as it will have little influence under wider throttle opening use. It's just modulation of small amount of air with throttle plate closed.
In field "guerilla" test for IACV, with vehicle off, turn ignition on but don't start ( this should prompt IACV to open) turn off again then remove loom plug from IACV. This should leave IACV open with no control from ecu, now start it and it should go up to 2/3000 rpm as the ecu cannot close the valve to control additional air. Now switch off, reconnect IACV and start it again, control should be back in range now and prove the hardware is working.

TPS, old type with slots, you have to move it to give baseline report to ecu hence the slots. Later systems the ecu asked for report from TPS and then used that as it's baseline during ecu boot as far as I know. So in effect you can't set it as it "calibrates" each start time and makes the slots redundant.
If you just unplug the TPS and run it without, it should just pick up air volume from MAF then use just that data with default map to run competently, but without response it gets on throttle opening abruptness. If it improves with TPS unplugged it suggests there's a fault there.

I'd guide against setting base idle speed until you have it debugged, it needs to have everything working to properly set it else you can just "transfer" another fault to be included in that calibration routine, it rarely needs setting unless someone has moved it in the vain hope that it's going to improve something, that often happens though.
Where is the temperature sender located on the 1992 3.9 engine?
 

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Dont forget Jack - the coolant temp sensor and the fuel temp sensor are quite close to each other. Looking at the front of the car the fuel is on the left (on the fuel rail) and the coolant on the right. They are very similar in appearance.
 

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As Range123 says, it's easy to have these plus an injector plug confused such that it makes an error. Worth carefully verifying to make sure your not caught in a trap that's effectively invisible to first inspection.

We've seen them on here with plug (same end terminal) swapped with the temp sensor to give this type of fault. It may have been swapped with #1 injector if I remember correctly, gave a very odd running like this as ecu had no temp read plus one cylinder not firing at all, which helps to cap the rpm.

Basic cylinder check, start motor and run for 15 seconds from cold, then switch off and put your thumb onto each exhaust port. It'll soon show you if one of them is not firing.
 
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