Hey everyone about a week ago on the day my truck clicked over to 220,000 miles it started to lose power while on the freeway, the engine slowing down regardless of pedal position. I thought it was the VSS except the speed on my ultra gauge read correct. I was on the freeway yesterday and it started losing power and misfiring, limped home just barely making it.
This morning I started it and at first it was running rough sounding like all cylinders weren't firing, but after it warmed up it seemed to start using all cylinders but then it began to surge up to 1200 then down to the 600s, almost dieing. Any ideas?

 

Sounds like an intermitent issue that didn't set a code. Could be something just slightly out of spec. You might remove the Idle Air Control (IAC) valve and see if there are a bunch of carbon/oil deposits behind it which isn't uncommon. If so, clean out with carb cleaner. It's not a waste of time because the area behind the IAC does get clogged up on some vehicles. Also, as it's running, you could pull the IAC connector and see if it changes the idling (it should).

But that shouldn't have any affect while driving down the road. The IAC only controls during idle conditions and should be disengaged once off idle. Perhaps a newly failing crank position sensor or even the knock sensor?? Might pull the connectors and make sure the connections are good and clean (all connections actually). On my chevy truck, the way you test the knock sensor is to tap on the block with a ball peen hammer next to the knock sensor and watch the 'counts' on your scan tool. Sure enough it counts them! On my chevy truck, there will always be one knock after you star it up (the ECM causes a 'test' knock upon start-up). The only problem is on the L/R the knock sensor is down under the exhaust manifold, might be hard to tap under there.

Might consider cleaning the MAF sensor with Mass Air Flow sensor cleaner. Could possibly be a coil pack starting to crap out. Also double-check your ground cable really well. A lot of wierd issues with Land Rovers (and modern cars in general) come down to poor grounds. Make sure they're really good. Could put a fuel pressure gauge on it. The fuel pumps do crap out on these -- not sure how old the one on your truck is, and that could lead to a poor running situation. I've had them flake out once the pump (vehicle) gets warm. Does the problem occur more frequently when it is low on fuel (pump hot) vs when the tank is full (and the pump submerged in gas keeping it cooler)?

I'm kind of giving you a scatter gun approach, but these things could make it run rough like you described. I've had something like this happen on my Disco, but only a couple times and I haven't had a chance to debug it.

 

Thank you for the information! My rover wouldn't have been running for the past eight years without this website. So today I started by doing a compression test, the readings were
(1) 140psi
(2)160
(3)145
(4)160
(5)140
(6)155
(7)160
(8)140
After that I was lucky enough to already have a spare coil pack which I had bought from a crashed junkyard disco with 80k so I installed that.
When I turned on the motor it didn't pulse and seemed much smoother then before but went straight to 2000 rpm idle and stayed there for a minute before I turned it off. Tried again and it was the same.
I decided to clean the throttle body and it was pretty carbon-y, put it back together and the truck started up nicely and went to 800 rpm idle, very satisfied I drove it a few blocks and everything seems fine. But it has poor power and can't drive above 30mph or it starts running rough
So I cured some of my land rover withdrawal but the truck still needs work

 

Is it throwing any codes at this point? Do you happen to have an ultra gauge you can check readings while you operate it?

Just looking at some GM manuals (which have good decision trees and pretty similar stuff) here are some things they recommend to check based on your symptoms:
- Ignition wires/timing - Visually check for black electrical jumps ..or ohm out
- Plugged air filter/fuel filter
- Vacuum leak
- ECM grounds & grounds to motor
- Injector wire connections and possible shorts (visually check)
- EGR Operation (does this even have an EGR??)
- Generator output voltage
- PCV Valve, pull out, put finger over pcv and release (do it several times), center valve should snap back
- Fuel pressure low?
- Restricted exhaust
- Water contamination in fuel. BTW, I had this happen really severe once about 5 miles after filling up ...I looked at everything up down and sideways, replaced a bunch of stuff, until I by chance noticed water droplets in the carb (classic car). It took me like 3 tankfuls and a lot of HEET (alcohol) to get it to where it would run right.
- Injector/s (for flow).
- Worn camshaft

 

Couple other things:

You might consider cleaning your Mass Air Flow (MAF) sensor too. I've seen similar problems cause highway conditions like you described. CRC makes a cleaner (OReiley's and other places). If you check on youtube or other places, you can see how to do it. The most thorough approach is to remove the actual sensor itself from the housing, but it's usually a more involved process. The results vary, but for many it works. I guess, give it a spray and see if it improves and if it does, maybe give it a more thorough cleaning, or replace. Ebay is the place to buy emission sensors (cheap). At least in my experience. I would definitely give it a cleaning though.

O2 sensor ..something to consider too. You should be able to back-probe all these sensors either at the sensor or at the ECM and check voltages so you can get a sense of what's going on ...or get an ultra-gauge.

I wouldn't discount the water in the tank theory though. ...as you drive and slosh fuel around, it might suck in some water that would otherwise lay at the bottom of the tank while idling in your driveway. Might try driving it on the Highway, then get back and remove the filter right away, catch all the gas as you take it off ..and dump whatever's in the filter into a clear glass jar and see if any water settles out. A tiny amount might be ok, but if you get a significant amount, that'll tell you something. Replace with a new filter. Use only Top Tier gas. If you could eliminate issues to zone in if it's fuel or ignition related that would be really helpful.

 

Look at the wiring to the crankshaft position sensor from plug to the valve cover clip. The insulation is probably deteriorated from exposure to 20 years of oil leaks. Very common.

 

yeah my crankshaft sensor was deteriorated because of oil so i can testify to that i think i need to double check the wiring again on it because I'm getting a very similar issue. As soon as i start the disco it goes to 2000 rpm then down to 600 then lower and then shuts off, i've checked iac and MAF and stuff so now I'm going to recheck the crankshaft position sensor wiring.

 

Did you do a thorough search of old posts in this forum? The high idle has come up a bunch of times.. There should be some good answers out there..

 

Mine had a constant high idle. Ended up being the TPS sensor.

Procedure on how I fixed it is on pages 4-5 on this thread: https://landroverforums.com/forum/di...o-84210/page5/

 

oh good to know i hoping in my case that the ecm just needs to adapt to the new lifters and that's why it's having idle issues so I've been driving around and it has been getting better but if it doesn't end up correcting it self ill probably replace the tps and/or iac/stepper motor.