This rover stuff is beyond me. When I was younger it seems diagnosing engines was pretty straight forward. But I just read all sorts of threads on acceleration issues and the list of possible problems is staggering. Many of you guys are waaayy smarter than i and have lots more experience with cars too. But anyhow, here's my current problem....maybe if I give you enough info someone will have the fix.
The wife came home from work 2 days ago and the rover was running fine. We jumped in and headed out to the store about 5 minutes later. The rig ran fine until I tried to pull out on the highway. I hit the gas to accelerate up to cruising speed and the dang thing sputtered and popped and wouldn't get up to speed...or even close! It seemed to not want to go above 2000 rpm. It was choking and popping and seemed to be missing on different cylinders. Limped back to the garage and tried to gun the engine in neutral. Still wouldn't rev up just a lotta choking and sputtering and random missing and popping.
Next morning I fired it up and it revved up just fine! I took it out and ran it till the engine reached normal temp. Then the same problem kicked in. No matter what gear I tried I couldn't get above about 30 mph.
I had pulled the VSS a couple weeks earlier because it was bad ( usual symptoms...random cutting out and speedo jumping around) and had been driving with it disconnected. It was running great since I disconnected it, so I don't think it is a related problem but I rebuilt it and installed it today just on the off chance that it was related. Ran it a while with no problems. But after warming up the engine, the rig refused to accelerate again.
Soooo... assuming the VSS is not the culprit, What would cause the old Disco to be unable to rev up after warm up? I don't have a pressure tester for the fuel rail. I don't have access to computer code read out. (Autozone is too far away to drive to). I doubt it's a clogged cat. But I could be wrong. Seems a bum fuel pump or fuel filter would act up hot or cold. I don't know where to start with the diagnosis on this one. The big clue here ( I hope) is that it only happens after warm up.
What think ye Mates???
It's a 98 le with about 190k.

 

If you have the impression that it starts just that little too easily when the engine is really cold (I had that distinct experience) there may be some over-fuelling taking place.

The reason for a way too rich combustion mixture which becomes excessive when the air thins out as the temperature increases could be a blocked air filter or leaking injectors, or combination.

After a run when the engine is still warm remove the spark plugs. Soot will indicate a leaking injector at that cylinder. (I have six of them, Discovery I with 193K miles). Replacing the induction air filter and ensuring a good spark with new plugs and leads alleviated the immediate embarrassment. The injectors will be replaced in time.

The symptoms you have may also indicate an imminent failure of the ignition amplifier module (which has replaced the old style condenser - yours will be next to the ignition coil next to the radiator. They are heat sensitive when about to fail. Your local parts shop may charge you up to $560 for this little bit of electronic silliness - I got mine for $31 on the internet, exactly the same as the one the shop offered me.

A very sooty black exhaust will confirm the above issue of over fuelling - be sure to check it too.

 

By the way - there my be another problem which is unrelated to the actual engine temperature but more to the time after starting off - namely a blocked air vent in the fuel tank. Test for that by undoing the fuel cap while the engine is suffering - there should be an immediate return to normal operations if under-fuelling due to a vacuum in the tank is the problem.

 

Sounds similar to my failing ignition coil issue. Also unbeknownst to me, I had spark plug wire that was flapping against the hot exhaust manifold. Burned a small hole in wire, every so often it would contact the manifold and do exactly what your describing.

 

Last tuneup?

Quality plug wires?

Hose connected on the fuel regulator?

I would try disconnecting the vsS again

You need to have codes checked readers are cheap, ultra gauge is like $70 and reads and clears codes plus display live data

Could be crank sensor going bad, when warms up and acts up pour water on the sensor see if the cool off helps

Loosing coolant?

 

any signs of running rich, maybe coolant temp sensor ?? check the real time temp reading with a UG or similar, the dash temp gauge is only there for decoration

 

There is also the fuel temp sensor

 

Thanks for so much help guys. I'm a little bewildered at all the possible suggestions. Most of those items i don't know anything about or where they are on the rig. But...
A few of these things i can obviously check easily. I like the fuel cap idea! Sounds about my speed. AND I often have trouble when fueling up because the air vent doesn't allow the fuel to go in fast enough. Isn't there some code that comes up when the gas cap is off?I can do that 1st.
I checked the air filter right away. It's not that.
One of you mentioned the coolant temp sensor. That reminded me that I had the check engine light come on a little while back. Autozone did a code check for me and came up with that but I neglected to replace it since there were no symptoms and I don't know where the thing is anyway. Then i forgot about it completely. Would that cause this??
Tom asked when the last tune up was. Had to laugh a little . The better question would be 'when was the last time i DIDN'T have to do something to the Rover.' Seems I put new wires on not too long ago. This doesn't feel like bad wires though.
And also, it is a totally different symptom than the VSS. This is a random missing whereas the VSS drops one cylinder.
And what/ where is the fuel temp sensor? and the crank sensor? and fuel regulator hose?
Sorry to sound obtuse, but I seriously don't know where they are.
I appreciate everyone's suggestions. Sorry if i didn't specifically mention each one. I'll be trying out a few this morning and letting you know what I find.

 

When I had trouble fueling it turned out my fuel sender was bad also gave drivability issues, you need a scanner or something showing live data

 

I had a similar issue, no power especially in passing situations or going up hills at highway speeds. The remedy was a new fuel filter. If it only acts up under higher-load conditions, that would be what I'd check next.