Greetings. Looking for any insight on my ’06 LR3 4.4L V8 that is currently in limp mode and have not been able to clear no matter what I try. Bear with me as there is a bit to share here to provide full context on the issue(s).

Symptoms:

Very rough and high idle when not in Park or Neutral. Generally runs high around 1,200 – 1,400 RPM and then will settle down to about 700 and idle very rough. While idling high, a slight touch to the gas pedal will drop it back down to the 700 range but shortly thereafter it will jump right back up to the 1,200 – 1,400 range (timing changes, sometimes sooner than others). When in gear, everything seems to settle down and run smooth, as expected, but in reduced engine mode. Does not run rough at all.

Codes are reported below. I’ve cleared the codes numerous times and initially they would basically all come back. More recently, the codes returned are basically the three with asterisks below at the top and the others seem to have disappeared. Codes are:

*P0102 – MAF Sensor ‘A’ circuit low
* P2103 – Throttle Actuator ‘A’ Control Motor Circuit High
*P2105 – Throttle Actuator Control System – Forced Engine Shutdown
P0607 – Control Module Performance
P0121 – Throttle/Pedal position Sensor/Switch ‘A’ Circuit Range/Performance
P0459 – EVAP System Purge Control Valve ‘A’ Circuit High
P0447 – EVAP system vent control circuit open

What I’ve tried:

More detail on this below, but so far I have replaced the battery, replaced the MAF sensor, replaced the fuel pump relay, and replaced the air duct intake pipe.

I own two of these and do most of the maintenance on them myself so am pretty familiar with the cars. However, I don’t have much knowledge/experience in the electrical realm and this issue very much feels like an electrical issue.

To get the car running, I have to first do a fresh clear on the codes. If I don’t the car will turn over and start up, and within 1-2 seconds, it seems the throttle body plate closes and suddenly dies. I should clarify that it feels as though the TB plate is closing but I’m wondering if it’s just getting an immediate signal to shut the engine down. If I do a hard reset on the car (remove terminals and connect for about 30 minutes) the codes still seem to be stored because the exact same behavior happens, meaning it starts up and immediately shuts off. I’m struggling to understand how the codes are stored after the hard reset which makes me wonder if the immediate shutdown is actually triggered electronically from the ECU instead of a mechanical failure somewhere.

Here's how I got here:

This all started several weeks ago. We started to hear a small, repetitive knock in the front of the engine some time ago that seemed to be getting progressively worse. After looking at things, it seemed there was a little play in the serpentine belt tensioner so picked up a new one and installed. When I was putting things back together I noticed the fan seemed a bit tight but didn’t think too much of it. Buttoned things up only to realize the knock was still there but seemed subtly different. After consulting the forum, I was convinced I needed a new fan clutch so ordered one for replacement. The order was shipped when I was out of town so I had my dad install it since it’s an easy job and I was gone for some time and hoping to get the car running again. He installed and indicated it was idling high but he thought he still heard the sound. I told him to go ahead and shut down and I’ll look at it when I get back. As it turns out, the knock was only coming from the fan just barely hitting a small piece of the plastic shroud surrounding it after some work I had done some months ago. So yeah, I’m a dumbass, but that’s a long thread for another forum 😉

Upon my return about a week later, it took me maybe a dozen attempts to finally get the car running. Initial attempts were as described above. Would turn over, idle high and immediately shut off 1-2 seconds later. I was thinking the alternator was going out. I finally got the car to run and while running, I measured the voltage on the battery with various devices on and giving some gas. I was reading around 14.4 volts which convinced me the alternator was fine. However, the battery was reading around 11.4 volts. Ended up having some bad cells so replaced the battery. Same issues on the truck continued.

I then wondered about the fuel pump and fuel pump relay. I have replaced the relay, and before doing so, I jumped the relay to confirm that the fuel pump was working. All seemed in order there but went ahead and replaced the relay with a new one anyways.

I was then focused on the air intake and throttle body. Throttle body was a little dirty, but nothing to be concerned of. Cleaned anyways just to be sure. This was prior to replacing the MAF sensor so also removed and cleaned that at the same time. When doing that, I noticed that I had some major cracks on the air intake duct on both sides (the side facing the MAF sensor as well as the other side where the hose runs to the throttle body). I thought I found the issue. Replaced it, expecting issues to be resolved, but the exact same issues continue.

Afterwards, I found a guy on the forum describing nearly identical issues. His problems were from his MAF sensor having a short to ground. Used a multimeter to make sure I was getting adequate voltage, around 5.5 volts, and then made sure it was grounded. Tested the harness to the MAF sensor, the throttle body and the fan. All checked out. Only thing worth mentioning is that the fastening clip on the harness to the throttle body was broken, but seems to be seated just fine. As a last resort, went ahead and just bought a new MAF sensor form AB and installed. Afterwards, cleared all codes and did a hard reset again for extra measure, but no luck. Same symptoms persist.

If anyone has read to this point, kudos to you, I owe you a beer. If you have any suggestions, I’m all ears.

All I know is, the car was running absolutely fine prior to me deciding the knock sound was something I needed to fix. At some point in disturbing the top front of the engine (e.g. air intake to throttle body and fan) this issue has popped up, and to me, seems to be an electrical issue of some kind, not necessarily a mechanical failure. I’m thinking about just replacing all the harnesses on those three areas as a final last resort even though they seem to check out with the multimeter.

And also, I’ve never had a situation where I couldn’t clear the reduced engine performance for at least a short while, so that is a new one for me.

 

Code P0121 throttle/pedal position sensor, had a bloke come to me with a problem where when he would hit the gas to pull away it would go straight into limp mode and virtually shut down.
This was a TDV6 model same as mine so the TPS is on the acc. pedal not on the throttle as in the petrol versions - worth a look anyway.
He replaced the pedal/tps assembly and back to normal.