Hello, I own a 1995 LR Discovery 1 and like it better than my 2017 one! It has 178K miles and in general runs great. Recently though it began running rough at idle. I changed all the spark plugs, cleaned the O2 sensor, and changed the fuel filter.

The truck has better power after these 3 fixes and runs perfectly on the highway or up a hill. But when I hit a stop sign, it's hit or miss as to whether it enters a rough idle mode. If it does, it begins to backfire and loses most power.

But I hit on a quick fix which is that if it does this, I simply turn the engine off, and upon restart, she hums perfectly and I'm off with full power.

Does anybody have any ideas as to this strange behavior and how to fix it?

Thanks!

 

Could be sticky or dirty Idle Air Control Valve (IACV). That valve gets repositioned when we stop and start the engine.

Get in there with some good carb cleaner. Clean up the throttle plate too (back edges included). If the IACV is really dirty, you may want to remove it for cleaning (and renew the gasket), then you can really get at the bored passageways too.

Probably also want to make sure the PCV orifice, passages, and oil separator are clean. PCV tune up kits with fresh rubber parts are available and easy to work.

 

Seems reasonable! Will try your suggestions and get back to you. Thx!

 

Followed all your suggestions, but most importantly bought a new IACV on Amazon for $15. The new one did not come with a gasket but looks sturdier.

That clinched the deal and she is now humming like if I'd just taken her out of the showroom.

Thank you VERY much!!!

 

Congrats on getting your issue fixed. I've had similar problems and cleaned the IACV previously but it's occasionally come back--acts like the idle is set just a bit too low. I'd just as soon replace it at this and for $15, why not? Did you just re-use the gasket from the old? IIRC, mine was super fragile, almost egg-shell like. Just curious.

edit: looks like it's metal-to-metal with an o-ring. I may have been thinking about something else....

 

Just to close this book for future travellers, I also replaced the IACV (like the OP), and also checked all of the vacuum lines per the sticker in the engine compartment. the hard line to the charcoal canister had been rubbing and it *may* have been leaking, so I epoxied it and wrapped the whole thing with electrical tape and zip tied it different so it wouldn't rub again. The small line that I think is labeled fuel pressure regulator (could be wrong about that, but it;s the small thing near the firewall that routes directly into the plenum) was cracked. Replaced that with some spare line and put everything back together and it ran like nothing ever happened. Took reading from the GEMS app and reset adaptive values and everything seems to be OK.

IACV I ordered was "QUALINSIST IACV IAC Idle Air Control Valve ERR4352Fit for 1997 for Land Rover Defender 90, 1996-1999 for Land Rover Discovery, 1995-2002 for Land Rover Range Rover iac motor" on Amazon and it uses a rubber o-ring instead of the gasket on the original. I cleaned out the throttle area and butterfly while I was in there. Looked like there had been blue loctite on the screws at some point so I added a couple drops as well.

 

I thought my issue had been solved with the IACV valve, but no, it's back with a vengeance.

To recapitulate, I have put in new spark plugs, new fuel filter, new wires from the distributor to the plugs, and a new IACV valve. Oniy after it warms up and runs perfectly, when I stop, idle will become rough and the LR loses much power. A quick off/on on the ignition cures it, and all is well until my next stop.

Beneath the passenger seat the diagnostics device shows an error code of 45.

My usual mechanic tells me he is stumped and that I need an old LR specialist since he cannot fix anything without his trusty OBD device which is useless on a 95 LR Disco.

Ugh!

Does anyone have any other suggestions? Maybe some British thoughts on the subject? Thanks!

 

Code 45 - Lambda sensor B - right bank. This is from a list of code I found on this forum.

I would clear the code(s) first of all. And remember, our code display only shows one at a time, so after clearing this one, there may be another (or others) to tackle.

 

Have you inspected and/or cleaned your tk's throttle and butterfly valve? They can get gummed up and just some deposits can cause rough operation. Clean with a plastic brush and some throttle body cleaner.

2) You can't really clean off an 02 sensor. maybe it's time to replace it. Also, the downstream 02's don't affect operation.

3) Get a propane torch with a piece of hose on the end and wave it around the engine compartment when it's 'missing'. Quick way to find a hidden vac leak.

4) Check voltage on the MAF sensor. Clean that.

5) Check/Replace PCV valve

6) EGR's can plug up cause rough running.

7) Coil packs sometimes get flaky when warm (Ohm out)

8) Maybe one of your new plugs is defective, or the porcilean got cracked during install (I've had that).

9) Check IAC again. Clean bore with an appropriate brush.

10) Ohm out new plug wires.

 

Mark G makes some good points for general maintenance and troubleshooting. Some points do not apply to the 94-95 models. For 94-95 there are only two O2 sensors (none downstream), and no coil packs (only one coil with an 8 pole mechanical distributor), no EGR, and no PCV valve (there is an oil trap and orifice set up, but not a valve). Even more impactful is there is no OBD2 port, only a Land Rover code display (with 2 digit codes), and it only shows one code, even when there are multiple codes set.

Maybe the $15 IACV was too good to be true. You might try to find an original LR part. I guess $15 was worth an experiment, but maybe it failed.