Hi all,

I have a 1996 Disco 4.0L auto with about 220k miles. It has never had any problems in my six years of ownership but is suffering from a weird shifting issue that might be throttle body related. The transmission itself shifts fine, but:

If I drive it really slow and non-aggresive and very light on the gas pedal, it will shift very lazily but otherwise drive just fine. Alternatively, if I press the gas pedal very hard (say, more than halfway travel), it's as if a sensor goes haywire and all the sudden the car will not shift into the next gear until 2500 to 3000 rpm. After this happens, the car will drive like that until it eventually and slowly starts shifting into gears at lower and lower rpm's until it is about normal (takes about a week of driving). If it gets back to about normal and I press the gas pedal down to the floor at any time, it will start all over again.

This is directly related to the gas pedal movement, which leads me to believe that it might be throttle body related or a sensor around that area.

I have even tested it when the car was back to driving nearly normally... in the morning before I started it, I pressed the gas pedal all the way to the floor and realeased it, and upon start up, the shifting problem started immediately with tell-tale revving up really high upon start up in park before I even put it into reverse or drive, which strongly supports the theory above.

Any opinions or thoughts much appreciated!

 

Kick down connection may need adjustment or lube or PB Blaster. See attached.

The throttle position sensor (TPS) could be flaked out, but it would make high revs, run rich, etc. You can watch the TPS readings with a scanner, it should go smoothly from about 9% to full. In some cases the throtle butterfly plate sticks on the gunk inside, that is what carb cleaner is for (don't use that on MAF).

 

thanks! Wouldn't a malfunctioning TPS or butterfly plate make it difficult for me to be in control of engine revvs? I will definitely check both of them to see if they are the culprit. I can control the revvs (for the exception of the naturally high idle rev in park and neutral), I just cannot control when it decides it wants to shift into the next gear. Thanks again!

 

Thinking on it a little bit more, if it always idled high in park and neutral I would think it was something mechanical like the butterfly plate but since it will only idle high when it has the shifting issue, I am inclined to think it's more of a sensor or a reading that is malfunctioning. I will go ahead and check that sometime tonight or tomorrow, thanks for the advice.

 

The D1 does not have an electronic transmission, the shift points are rpm/pressure based. There is no electronic sensor that can send a signal to a D1 transmission, no tranny ECU, no CAN buss, etc.

The IACV controls idle, and the coolant temp sensor can be bad and make a higher idle.

 

I would be inclined to inspect the throttle cable from the gas pedal to the throttle body or the linkage itself. The high idle and late shift are related in that the linkage is not returning to idle position, causing the idle to be high since the TPS reading is showing an open throttle plate and the cable for the transmission has tension on it as if the gas pedal were partially depressed.

 

A good point about a sticky subject.

 

Check the throttle cable when the engine is off.
Should be a tiny bit of play or slack.

Same with the other cable which is the TPS.

Do the same for the Cruise cable.

Just a tiny bit of slack.
Then, you'll be fine.

One of the cables is too tight way too tight.

loosen the nuts with a pair of 10mm wrenches and draw the cables in closer until there is just a little slack.

The throttle must CLICK against the stop on the throttle body.

 

The other cable is the TPS? WTF!!!!

The TPS is solidly bolted to the throttle body at the end of the shaft that operates the butterfly.

I cable comes from the the gas pedal, the other goes to the transmission. The second cable is not a detent cable or a kick down cable. It's proper name is throttle pressure cable, it's a mechanical means to tell the transmission where the engine throttle is at any given time.

 

The tranny in my 96 disco was running strong...got stuck in high range...didn't abuse it but then it quit pulling in all forward gears. Reverse seems to work ok...forward gears nothing at all.

Has anyone ever experienced this before or is it time for a new transmission?

Thanks!