Disco 1995 unknown issue

Hello everyone! I've got a 95' Discovery 3.9L and am having a random issue and no-one near me seems to have a clue about what to do. When I get to 30 mph, the revs start jumping up to about 1.5k and dropping to 1k... back and forth... slowly losing speed. I can get past this by kicking down, but when I drop back below 30, it does it again. I love this car so any advice would be greatly appreciated!!!

It could be a throttle position sensor on the way out.

I've been doing some driving to see if I can narrow it down more. I've found that:

-When I put the car in 'P' and put in in 'R'. The car makes a very big jerk motion when selecting the gear and setting off. Enough to shake you in the seat.

-it seems to be on 2nd or 3rd gear when going at 30mph that the car struggles.

-from what I can tell, it only happens when I turn the car off and back on within an hour or so. Doesn't seem to do it from cold.

Does that still sounds like a TPS issue?

Thank you for the help!

Dan2000 said:

I've been doing some driving to see if I can narrow it down more. I've found that:

-When I put the car in 'P' and put in in 'R'. The car makes a very big jerk motion when selecting the gear and setting off. Enough to shake you in the seat.

-it seems to be on 2nd or 3rd gear when going at 30mph that the car struggles.

-from what I can tell, it only happens when I turn the car off and back on within an hour or so. Doesn't seem to do it from cold.

Does that still sounds like a TPS issue?

Thank you for the help!

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The clunk going into reverse is a gift from Land Rover. All 3 of mine do that.

It could be an air intake sensor.

Try manipulating the TPS. Mark the existing position of the TPS and the loosen the sensor a bit and rotate it a squeak, not much, and take it for a drive. Try different directions of rotation as well. I had this problem on my '93 RRC.

The clunk the D1 auto has when selecting R is from the transfer box, my D1 does and the RR before did from day one, but its only when the oil is hot and moving the selector from D to R.
A jerk motion when selecting D or R or both can be caused by an engines high ideal speed.
With the 30mph issue its crystal ball time, from fuel restricted to and iffy throttle position sensor or plugs, leads or dizzy cap etc etc.

If u can adjust the TPS then in must be an early engine, with the later disco “serp” 3.9 engine there’s no adjustment.

discool said:

The clunk the D1 auto has when selecting R is from the transfer box, my D1 does and the RR before did from day one, but its only when the oil is hot and moving the selector from D to R.
A jerk motion when selecting D or R or both can be caused by an engines high ideal speed.
With the 30mph issue its crystal ball time, from fuel restricted to and iffy throttle position sensor or plugs, leads or dizzy cap etc etc.

If u can adjust the TPS then in must be an early engine, with the later disco “serp” 3.9 engine there’s no adjustment.

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Thanks for the education, discool. My 93 is a LSE with the 4.2 lump and I assumed they were the same.

Boy are those TPSs going for stupid money.

Western Slope Rover said:

Thanks for the education, discool. My 93 is a LSE with the 4.2 lump and I assumed they were the same.

Boy are those TPSs going for stupid money.

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TPS! I was going to say best of luck with that ‘if you can get one’ my 3.5 TPS had the elongated screw holes, my later disco 3.9 doesn’t, by all accounts the ECU now takes into account if theres any variation due to wear, anyway it’s obsolete now, as its a vital part I wish I had purchased a few, back when I could pop into my local main dealer and possibly get a box full

And regarding the LSE I remember rows of them waiting to board a ship in Dover Harbour, thats in the days when I plus the RR popped over to France on a booze cruise that was popular at the time.

discool said:

The clunk the D1 auto has when selecting R is from the transfer box, my D1 does and the RR before did from day one, but its only when the oil is hot and moving the selector from D to R.
A jerk motion when selecting D or R or both can be caused by an engines high ideal speed.
With the 30mph issue its crystal ball time, from fuel restricted to and iffy throttle position sensor or plugs, leads or dizzy cap etc etc.

If u can adjust the TPS then in must be an early engine, with the later disco “serp” 3.9 engine there’s no adjustment.

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Yes I have the 3.9 so can I not adjust the TPS? Sorry, I'm a bit of a novice when it comes to land rovers, my Volvo 240 recently died and I've picked this up- still learning!

I've noticed, when I put the car in 'D' and press the throttle, the front of the car rises, as if the handbrake is on... then it will jerk forward and move on. It doesn't happen all of the time though. Any ideas? Thanks everyone for your help!

Dan2000 said:

Yes I have the 3.9 so can I not adjust the TPS? Sorry, I'm a bit of a novice when it comes to land rovers, my Volvo 240 recently died and I've picked this up- still learning!

I've noticed, when I put the car in 'D' and press the throttle, the front of the car rises, as if the handbrake is on... then it will jerk forward and move on. It doesn't happen all of the time though. Any ideas? Thanks everyone for your help!

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It your engine has a serpentine belt then NO you cant adjust the TPS.
I’m not familiar the the earlier disco 3.9s with the V belts so they may or not be able to be adjusted, anyway there should need too as its a factory setting and will have a dab of paint on the screw head, the only difference between the two TPS is one has elongated screw holes to enable some adjustment, something like 5mm each way from centre.
Again the base idle adjustment is a factory setting and there shouldn’t be any need to touch it, like the TPS, unless of course theres been a major repair of the engine.

Possibly the hand brake is still applied, it not unknown for it to not fully release when the lever is released, ie something is sticking or adjustment required ie. mechanism or cable
Try not applying the brake and still in P when parking.

I’ve e forgotten a couple of times to release the hand brake but haven’t notice the front of the vehicle rising just a bit sluggish moving off. Ooops the hand brake is still on.

So, quick update. I've noticed all of the symptoms only occur when I restart the car after having driven it recently (within the last two hours). On the first drive of the day, the car is smooth and has no issues. Any ideas??

Dan2000 said:

So, quick update. I've noticed all of the symptoms only occur when I restart the car after having driven it recently (within the last two hours). On the first drive of the day, the car is smooth and has no issues. Any ideas??

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“All of the symptoms”? So are there more than ‘the vehicle rising’.
So its still with there with the handbrake not is applied ? The brake drum and transfer box gets warm even hot when the vehicle is driven.

discool said:

“All of the symptoms”? So are there more than ‘the vehicle rising’.
So its still with there with the handbrake not is applied ? The brake drum and transfer box gets warm even hot when the vehicle is driven.

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I'm wondering if it might not be worth backing the handbrake off a tad just in case it is binding a bit.
Or stripping it down, i.e. inside the drum, to see if bits of it don't need lubricating.

No, I've stopped using the handbrake handbrake I stop and only putting it in park. This has stopped the 'rising' issue. I was talking about the previous 'rev' issue. Thanks for the help!

Dan2000 said:

No, I've stopped using the handbrake handbrake I stop and only putting it in park. This has stopped the 'rising' issue. I was talking about the previous 'rev' issue. Thanks for the help!

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Ok but as I said in post #5 its crystal ball time, so could be as simples as iffy fuel or air filter, crankcase breather, Iff connection at the coil top or at the speed sensor thats tacked on the side of the transfer box, it’s really any other connection that’s associated with the ignition system to look at.
A bottle of fuel system cleaner in the petrol tank once a year sorts out my engines lumpy idle issue it use to have so how simples is that.
If your engine has done a high mileage and not had a regular service, there now could be a worn component to find & replace,

Stanleysteamer said:

I'm wondering if it might not be worth backing the handbrake off a tad just in case it is binding a bit.
Or stripping it down, i.e. inside the drum, to see if bits of it don't need lubricating.

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Could need looking inside the drum, hand brakes on autos don't have a hard life, ok backing off the adjuster a turn, better still following the LRs adjustment instruction to set lever with the brake being on with 3 clicks.