If you have a good mechanic and he reads the codes for free then let him do it.
If you are getting mis fires then you need to start with the basics, plugs and wires.
And not cheap plug wires either, STI or Magnecor plug wires.

 

I took it in to my mechanic and this tiime the code was misfire on cylinder 5 and 7. He said that he checked and some of the spark plug caps were loose and he tightened them.
Well this did not work at all and misfiring started again almost as soon as I drove it away and the check engine light came on again. I am pulling the plugs myself to check them today.
The first one out shows it is a DENSO W16EXR-U and the gap measures .030". No sign of fouling but the little cap on the end was loose.
I seem to remember that this whole problem started when I changed the regular to premium fuel at my mechanics recommendation. One tank of premium and the misfiring started shortly after that. I thought it was the plug wires and I changed them out and sure enough it ran well for about 1500 miles before it started misfiring again.

 

First things first...
These trucks REQUIRE premium fuel.
You CANNOT use cheap plug wires, autoparts store brand plug wires will not last a month.
Use any spark plug you want, just make sure its gapped properly and use the same on all 8 cylinders.

 

I cannot argue that the vehicle is specified to use premium fuel. I can report on my experience which is that I did not check when I bought it, and I drove it from 40 K to 100 K on 87 octane fuel and never had any problems at all, no knocking or anything.

I think another possible cause of my lack of power problem is a defective throttle position sensor which would explain why everytime I back off and on the throttle the lack of power/misfire goes away momentarily.
I am checking on the plug gap now.

 

From the sounds of other posts on this site it sounds like a dirty throttle body or intake valves could also be causing some problem since I have never cleaned the throttle body or done and induction cleaning.

So I think this week I will have the following work done:
Remove plugs, check gap and check for fouling and replace as necessary.
Replace throttle position sensor.
Clean throttle body.
Induction cleaning.

Hopefully that will cause the problem. Oh yeah, fill up with premium fuel and add engine cleaner to the tank.

 

I thought the exact same thing, because I too can let off the throttle and back on and the issue goes away momentarily...

I replaced the TPS and it changed nothing. Save your money. I have 3 TPS's. The original, a known-good used one, and a new one. No matter which one is in the truck it drives the same. Unless it's in the wiring for the TPS, its not the TPS.

Also - I cleaned the throttle/butterfly and just about anything you can imagine with no change. I've done everything but rebuild the motor. Not trying to discourage you, just offering additional info as it seems we have the exact same problem.

Let me ask you this:

While you're driving and it's misfiring slightly, does it ever just "kick in"? Kind of like something turned back on, or opened back up? And for a few moments it drives like a damn dream?

-Justin

 

Yesterday I decided to have a close look under the hood myself. I found that the hose clamp securing the air intake hose to the throttle body was completely loose, and two of the clamps holding the air filter top on were loose. I tightened all this and no more faltering and missing. the problem went away completely.

So far I have driven 75 miles without incident.

 

Thank you for reporting back.

 

Often times folks crap all over the Rover in its many variations... whether it is because of the "British" engineering design, the curse of Sir Lucas or the reliability and performance myths, it makes no difference. Most often we find the simplest test of components or just a close inspection under the hood will yield causes and solutions.

(Usually) We could have spent days and multiple posts on this forum guessing at the most common issues related to various symptoms that we've all experienced similar to Wlundquist's. "It IS this sensor"..."I hate this Truck!".

In the end it was just a stupid unmetered air leak... a loose clamp!

Good use of the KISS method Senior Lundquist.

 

Goddammit I wish I had the same luck. Although I'm not sure how anything you found would even cause those symptoms.

Glad you tracked it down! Enjoy.