My '97 Disco I is a great vehicle, with 200K on it, but this problem is beyond me and looking for some advice. While it starts and idles great, it can't get past ~1750 rpm, just backfires and sputters, when returned to idle its fine, silky smooth rpms. Checked TPS from ECU connector, min-max, .7 - 3.7 kOhms, .6 - 4.3 V across potentiometer. Smooth changes in both as I cycle throttle. The 1750 rpm limiting would say TPS but with these results it would seem ok, I think. I can add that when I disconnect the TPS it jumps to the high idle setting, as expected.

I cant imagine there is a connection but this happened about the same time my coolant reservoir tank exploded. (missed that posting) I changed the tank out and then ran into this problem when I started it back up. Fluid level seems constant so not suspecting any head gasket issues. Maybe coolant got into something

I would REALLY appreciate any advice on what it could be. Current price for TPS is $144.

Thanks

 

Check Engine Codes.......? If light is not illuminated check the CEL bulb in the dash card because it should be lit. Scan it and it will be there.

And sorry to say but it's the TPS. The ECM is initiating fuel overrun cutoff. And that occurs at.......what for it..........what for it..........1750rpm!

The TPS range is 0VDC to 5VDC, not .6VDC to 4.3VDC. I understand it's idling fine but backfire and sputter is also a clear symptom of the TPS lacking throttle response hence TPS being at fault.

Because there is a throttle plate warmer right under the TPS when you overheated it probably effected the worn/old TPS and pushed it over the cliff.

Contact a used parts vendor (Paul Grant or Will Tillery) or find the GM equivalent TPS at your favorite parts palace, much cheaper alternatives with the current mileage on the clock that you have. I've bought from Paul and Will and both are awesome in the parts they choose to keep, seriously the best parts only.

 

Just reading another forum and one dude took his truck to a shop and had the voltage adjusted. Nothing more was stated in the post. Not sure how you'd adjust it for voltage......

 

With the 1750 cutout, and your point about it being cooked by lack of flow through cooling plate, it has to be the TPS. Great idea on used or alternative part, will check that out. Seems like there may be some way to stroke it and re calibrate TPS map in the ECU (have done that on BMW's) .

Will post the results, and hopefully fix it, thanks again.

 

Report back when fixed, how it was fixed, this is an important issue.

 

While it was a good bet, the new autozone (went big) TPS sadly didn't fix it, other than now it more precisely hits the 1750 limit, I can push it above that slightly for a 0.25 sec, but it backfires,sputters and immediately comes down. Idle is still very smooth.

When I installed the TPS RPM's went to high idle, as if it were disconnected. Figured the "adaptive" learning, aka trim values, had to be reset, so turned ignition off, then left key in accy mode and and moved accelerator pedal to floor before lamp test was over. (something I've done with other ECU's) That seemed to set the values. On the next start it idle exactly just where it should, but still no joy getting past 1750.

I did get a crankshaft sensor, will try that as well this evening.

 

What's your VDC at idle position and WOT?

 

It is about the same as previous, .7V closed, 4.3V WOT. Supply is a smooth 5V, when measured yesterday.

New development - Went after cover for crank shaft sensor, ridiculous, cover bolts inaccessible, cover deformed. In process guessing I pulled lead, or sensor fell apart, as I now (at least suspecting) have the classic "no start due to failed crankshaft sensor". It is a PITA to r&r, D2 looks much easier. Any tips/links on getting it out appreciated.

If it fell apart that easy maybe it was on it way to total failure and part of the problem.

 

Not uncommon. Mounting ears still attached? Try a cabinet screwdriver to pry it out.

 

Solved - ended up being crank position sensor. It was loose in its mount, and wire to it was down to just a few strands. Runs fine now!