I have '96 disco, and i have been having trouble with my rpm's. I've had it since august, and it seems to drive alright, but w/in the last two months its been acting up. it drives alright, but when i slow down or stop the rpm's drop (typically it bounces off the bottom followed by a brief blink of the oil light) but when i accelerate they jump right back up. i changed the plugs and air filter in sept. i changed the oil last month and also the battery (O'reilly's said the alternator was charging fine), and yesterday my fuel filter and also changed my trans. fluid. my acceleration seems to be better, but the problem is still occuring. also i have found that if i shift into neutral the same thing occurs, but if it doesnt on that time, braking has no effect-it just drops to ~700rpm. any ideas would be great.

 

So it tries to stall? Or it just drops to 500 rpm?

 

sorry, a few run-on's in that post. sometimes it stalls out, sometimes it drops to only 500, then others it will drop all the way down, bounce off the bottom and when i reaccelerate jump up real quick to normal.

 

CEL on? Any codes?

 

no light, no codes.

 

It could be the fuel temp sensor or the fuel pressure regulator. I have heard of both going bad, the temp sensor tends to cause more run problems and the pressure reg tends to cause more no start problems.
Have you cleaned the throttle body? Or done a induction cleaning? You might want to start there, both are cheap and you can do them yourself. Lets start simple first.

 

I just got over that problem myself with the same year disco. Its most likely your alternator. It may be charging fine but on those models the alternator also sends out a timing tick to your engine. In my case, i would get to about 2000 rpms and i would loose all horse power and start bucking, my rpms would also do the same as yours. To test it, take of your serpentine belt and take it for a drive, and try to get it to do it. not too long because your pumps and fans wont be on. you wont have power steering either.

 

Now your saying yours did the same thing. Your rpms would drop off like that (same severity)? what would driving without the serpentine belt do? does it put more strain on the alternator? thanks for the input, im getting desperate at this point.