Lars L Posted November 22, 2007 Share Posted November 22, 2007 varies quite a bit on my V8 Disco. Starting from cold it's fine, but often when I have driven it so the engine gets normal temperature, shut it off and restart a few minutes later, the idle speed is very low. Almost to the point that the engine dies when I put it in gear (automatic). Starting the AC making the extra air valve open is sometimes the only way to get a reliable idle in city traffic. So at least that is working... After a restart the engine also hesitates when I press the pedal after engine breaking, but when driving a while, it's fine again. I have been reading on different forums to get information and I have checked that all vacuum hoses and things are OK on the plenum chamber. I have also checked and sprayed electronics cleaner in all sensor connections I could get to, including the speed sensor on the transfer box and the AFM. I have read that the speed sensor, or transducer, sometimes is to blame for bad idle. Even Haynes mentions that, so it must be true, right? Can it be "shot" even if the speedometer seems to be doing all right? As the sensor is quite expensive, I would like to seek some input before I buy one just to see if it makes any difference. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 22, 2007 Share Posted November 22, 2007 The speed sensor can be shot as the speedo is less sensitive to rubbish signals than the ECU will be. I'd check and lean the idle stepper (lump on the back of the plenum with a 4-pin connector) this is what controls the idle speed, they can get full of crud and are known to cause problems. They're also £eek to replace, but I read a suggestion on Pirate recently that there's a universal replacement available for £cheap from somewhere or other. Quote Link to comment Share on other sites More sharing options...
Lars L Posted November 22, 2007 Author Share Posted November 22, 2007 I have been reading in the "book of lies", so obviously I can't vouch for its correctness. Anyhow, it says that the air valve opens when "instructed" by the ECU. For example when the AC is switched on. When I do that, the revs go up at once, so I presume that the valve is functional. This was the first thing I looked at. I took it out and cleaned it some time ago, still looking fine to me. Well, I won't be ruined by buying a new speed sensor, so maybe that's the way to go forward. Thanks Mr Freezer! Quote Link to comment Share on other sites More sharing options...
First_Fleet Posted November 23, 2007 Share Posted November 23, 2007 Try this. Remove the Air Flow Meter plug, with some pointy nose pliers slightly twist the flat male pins on the AFM. Bend back the rubber boot on the plug & ensure the cables are pushed in & secure. Replace boot. With some electronic contact cleaner, spray the pins & FM plug openings. Replace & support the plug with a cable tie or something suitable. Run engine. I saw this on another forum & it seemed to fix the problem for the bloke. Heat soak was thought to be the cause after it was left standing while hot, & appeared to be enough to allow the pins to lose contact. Re the Vehicle Speed Sensor. It has been a common source of complaint on various car forums that these split open at the moulded seam & allow moisture & road dirt in, which gathers inside the magnetic housing. Certainly had on mine. The old P/N was AMR1253 & the new part has SS to YBE100540 + O ring seal 571665 I assume the seam problem was rectified for this SS. *** As it is a sealed component, I very much doubt you were able to squirt cleaner into it & you probably only sprayed the outer plug connections. Quote Link to comment Share on other sites More sharing options...
Lars L Posted November 23, 2007 Author Share Posted November 23, 2007 Yep, certainly sprayed the connections only. Will look into it all later. By now I will enjoy the reassuring sound of my 200Tdi in the 110 for some time. Disco is only used when I have to... Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted November 23, 2007 Share Posted November 23, 2007 Does yor Disco run Oxygen sensors/Cats ? Quote Link to comment Share on other sites More sharing options...
Lars L Posted November 23, 2007 Author Share Posted November 23, 2007 Oh yes it does. I don't know why you are asking , but I have had the Disco tested at SBP (like the British MoT) a few days ago and the exhaust values were well within limits. Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted November 23, 2007 Share Posted November 23, 2007 Ok,I have no idea what your emissions limits are,but often if the Oxygen sensors a sluggish or given false info the info they give to the engine ECU can mislead it and give rise to poor mixture control.A failing ignition amp or bad cap /rotor/leads or plugs will give similar problems.Genuine ignition components are a must on a Rover V8. Did you get a print out of the emission test ? Quote Link to comment Share on other sites More sharing options...
Lars L Posted November 25, 2007 Author Share Posted November 25, 2007 I'm back again. Cap and rotor were changed from pattern to genuine a couple of years ago and the HT wires were changed to Lumenition Blue. That cured the misfiring that caused the most bother back then. And yes, I got a printout of the emissions, but I don't have it here. What I remember is that the lambda value is supposed to be 0,97-1,03 and that mine is 1,03. At last year's test it was 1,02. Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted November 25, 2007 Share Posted November 25, 2007 Ok at a Lambda reading of 1.03 it is running lean - hence the very low idle speed,very sorry but I've had far too much wine to think past that.I'll be more sober tomorrow and give you a sensible answer ! Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 25, 2007 Share Posted November 25, 2007 check all the engine air hoses, hoses to afm to engine and jubillee clip tighnesses etc, and top end joints (plenum to trumpet etc) for any air leaks Nige Quote Link to comment Share on other sites More sharing options...
Lars L Posted December 18, 2007 Author Share Posted December 18, 2007 Well, today I've changed the speed sensor. Very nice when struck with lumbago last Friday and with a knee that was twisted too much several weeks ago so it locks when I try to get up from the floor. I am going to make a roundtrip of some 650 kms tomorrow, first real test. The speedo worked anyway, so I must have done something right. Quote Link to comment Share on other sites More sharing options...
DiscoClax Posted December 22, 2007 Share Posted December 22, 2007 Try this.Remove the Air Flow Meter plug, with some pointy nose pliers slightly twist the flat male pins on the AFM. Bend back the rubber boot on the plug & ensure the cables are pushed in & secure. Replace boot. With some electronic contact cleaner, spray the pins & FM plug openings. Replace & support the plug with a cable tie or something suitable. Good advice on the pins. I tried this a week ago as mine has always been a bit erratic when running on petrol. Just gave them a slight twist and it's never run so well, or consistently. Thanks However my idle speed is still mental, as it has always been. Revs its proverbial off Not sure why a low-comp V8 needs to idle at over 1,000rpm... I'd also love to find a fix for this. Quote Link to comment Share on other sites More sharing options...
First_Fleet Posted December 22, 2007 Share Posted December 22, 2007 Pleasure, 'I'm here to help' (as Kevin Rudd recently said ) I do wonder though, how many badly idling V8is are running around when this simple fix might knock it on the head. DCx, you speak as though it does this high idle all the time, right? Have you removed & thoroughly cleaned the piston of the idle air control valve at the rear of the driver's side plenum? It could be fouled with gunk. It unscrews out, but when screwing it back in, tighten it no more than hand tight with some sealant on the thread. ie. the body at the thread step is quite weak due to it's design/manufacture. Next thing I would check, is the Base Idle Adjustment, & do that as per the W/Manual. I hope 2nd time is lucky. Hope this helps. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.