Why does my 3.9V8 now rev to 2000rpm on start up?

[duncmc]

I am after suggestions please.

In the last week or so when I now start the V8 it goes straight to 2000rpm. At first it stays there, but after perhaps 15 seconds it starts to adjust down in chunks until it is at normal tickover.

Does any one know what could be causing this?

I have checked that the thottle cable is not too tight, swapped the throttle pot for a spare, and checked that the throttle is actually closing properly at tickover. Changing the throttle pot didn't make any difference.

I can't find the correct bit in the workshop manual about setting the tickover speed.

It also seems to be a little slow to come off the throttle when driving it, again any suggestions?

I did clean the throttle assembly and regrease it when I had the pleunum off. The thottle linkages do look to be working correctly.

[Dave W]

Probably a sticking Idle air control stepper. Try unscrewing it from the plenum and cleaning it.

[duncmc]

Probably a sticking Idle air control stepper. Try unscrewing it from the plenum and cleaning it.

Thanks Dave, I found some reading material on the net and am suspecting the Idle air motor. I did unscrew it this afternoon, but didn't clean it. I'll give it a go, and I have a second hand spare I can try too.

[Hybrid_From_Hell]

Use brake cleaner and an airline

Nige

[duncmc]

Thanks Nige. I have just re-disocvered this link http://www.g33.co.uk/fuel_injection.htm. I will do the cleaning steps in there to clean the stepper and if that doesn't work, it says what else to check and set.

Thanks.

[duncmc]

Looks like my post after I had cleaned the Idle air stepper motor this morning dissapeared.

Anyway, I got the motor apart using the instructions in the link above and cleaned it with contact cleaner before reassembly. The start up revs were better at about 1600rpm, but still a bit high, and after a few secs it still then settles down to normal tickover ish.

So I am goin to have to investigate other avenues such as looking at the lamda values. I am considering an ECUmate, or trying to get the Roverguage software to work. Looking at the 2 it does look like the ECU mate is better even if it is more expensive.

[MikeAK]

Have you checked the base idle setting? If this is wrong it can give all sorts of weired idle faults including what you describe. Had the same symptoms on my RRC and changed the stepper twice before realising the base idle was wrong. Strange idle faults due to bad base idle settings are oftem mis-diagnosed as a sticky stepper. After setting disconnect the battery for a couple of minutes to clear the learnt idle positions.

You set it by pulling of the rubber pipe to the stepper housing and pluging the ends, then set the idle to the specified value using the bypass screw on the plenum near the throttle. From memory base idle spec for mine was 525 RPM but its all the RAVE manual if you want to check. Adjusment should be done with engine fully warm.

I have been using Rovergauge for a couple of months and its excellent no problems getting it to work and its practially free, only cost is for the FTDI TTL serial cable. I found one on E-Bay for £12.00. Shows all live values and fault codes, even shows the 2D load speed map and the current position.

Mike

[duncmc]

Hi Mike,

I haven't checked the base idle setting yet. There are a few other things I want to check first such as the lamba values. I definately have something weird going on or an intermitent fault. Tonight, the idle was spot on, but then it was hunting at traffic lights on red.

I think for £12 plus P+P it has to be worth a go with the Roverguage software. Does it show "actual" lamba values, or a % of max?

Edit: I have ordered a cable from ebay now. So when it comes I'll have a play.

[MikeAK]

Rovergauge allows you to view either short or long term fuel trims. The short term fuel trims will tell you what the lambda sensors are doing.

Mike

[p76rangie]

On start up the idle valve will be fully open and will therefore operate at the maximum revs the airflow dictates. You are obviously getting too much air at startup. Since to had the plenum off, it could be that you have a vacuum leak or to failed to connect the various hoses up correctly. Cleaning the intake will also naturally allow more air through, this will mean that you should screw in the base idle adjustment in to reduce the airflow. Forget about the adjustment in the manuals, just screw it in until your cold start up revs commence at around 1,200 RPMs before it starts to adjust itself.

[Bowie69]

I'd reckon you have an air leak somewhere, as you have cleaned the valve.

Check all hoses to the plenum, including the fiddly one on the back going from the plenum to fuel pressure regulator.

[duncmc]

I'd reckon you have an air leak somewhere, as you have cleaned the valve.

Check all hoses to the plenum, including the fiddly one on the back going from the plenum to fuel pressure regulator.

As I have recently had the plenum off etc, I know that is sealed ok. And that all hoses are actually on in the correct positions. The one that goes to the heater control is looking a little perished so I'll check that. I might change it anyway. I need to order a bit of water hose anyway for the LPG vaporiser because it won't stop dribbling coolant, and they do the small vacuum hose.

The cable to try the Roverguage software arrived today, so I just need a trip to Maplins to get a 390 Ohm resistor (400 if they have one) and a couple of connectors thn I can connect that up and see what it says.

It will be Saturday probably before I get there so no progress until then.

[MikeAK]

Coincidentally I was having a look a mates RRC on the car park at work today. He was having similar symptoms, high idle speed varying between about 1000 and 1500 rpm, different every time it was started. Whilst have a poke around under the bonnet I nudged the convoluted hose between AFM and plenum with my elbow, idle speed immediatly changed! Took hose off and it has a leak, not a split but worrn very thin with many pinprick holes where the convoutions seemed to have been rubbing against each other. The affected area was only over a couple of convolutions in the middle where it bends and only underneath where it couldn't be seen until removed.

Wrapped some self amalgamating tape round it and the idle was back to normal.

Probably worth pulling yours of an checking it

Mike

[Bowie69]

Also had that too.... duct tape was a good solution then

[duncmc]

Coincidentally I was having a look a mates RRC on the car park at work today. He was having similar symptoms, high idle speed varying between about 1000 and 1500 rpm, different every time it was started. Whilst have a poke around under the bonnet I nudged the convoluted hose between AFM and plenum with my elbow, idle speed immediatly changed! Took hose off and it has a leak, not a split but worrn very thin with many pinprick holes where the convoutions seemed to have been rubbing against each other. The affected area was only over a couple of convolutions in the middle where it bends and only underneath where it couldn't be seen until removed.

Wrapped some self amalgamating tape round it and the idle was back to normal.

Probably worth pulling yours of an checking it

Mike

Also had that too.... duct tape was a good solution then

Good idea. Thanks guys. I have a new one in stock. I can try that easily too.

[duncmc]

Bit of an update on this.

The car did start to rev lower on startup and is now seemingly back to normal. So maybe an intermittent fault.

I have got the Roverguage working today, and it looks interesting. I need more ime to play with it yet. One thing it did show at first was fault codes on the lambdas. Cleared them and it didn't come back...yet. I'll keep an eye on it.

[rafelius]

Hello LandLovers! I'm new here, but experienced with (by) LR V8. Haha it's gonna be nearly half year since I'm trying to fix my idling problems. I'm from Poland and I'm in love with my LR Disco V8 3.9 Hot Wire MY98 50th Anniversary Edition.

My question is to You guys, who are using RoverGauge (genius software btw!) I've got same problem like Old Hand - high startup idle - and rich mixture, probably permanent limp home mode. Could You share with my yours RoverGauge pictures?

I'm not sure does my lambda sensors has working OK. I don't have long lambda trim readings at all..Also short lambda trim seem to be "rich". It's just an example Prnt Scrn, Tomorrow I'll get readings from hot engine. I just can't find cure for high idle and black sooty spark plugs..

My point is, if I will know correct readings from RoverGauge than I could try to sort everything out. Ehmm...very sorry for my English

Sorry if I'm interrupting your topic.

Uh-mm.. maybe one more question... is it true that 14CUX need "some time" to adapt fueling after resetting-disconnecting battery? Cause I've just fixed too high fuel pressure (causing overfueling) but symptoms had stayed..

Thank you so much!

Best regards

R.

[duncmc]

Hello LandLovers! I'm new here, but experienced with (by) LR V8. Haha it's gonna be nearly half year since I'm trying to fix my idling problems. I'm from Poland and I'm in love with my LR Disco V8 3.9 Hot Wire MY98 50th Anniversary Edition.

My question is to You guys, who are using RoverGauge (genius software btw!) I've got same problem like Old Hand - high startup idle - and rich mixture, probably permanent limp home mode. Could You share with my yours RoverGauge pictures?

I'm not sure does my lambda sensors has working OK. I don't have long lambda trim readings at all..Also short lambda trim seem to be "rich". It's just an example Prnt Scrn, Tomorrow I'll get readings from hot engine. I just can't find cure for high idle and black sooty spark plugs..

My point is, if I will know correct readings from RoverGauge than I could try to sort everything out. Ehmm...very sorry for my English

Sorry if I'm interrupting your topic.

Uh-mm.. maybe one more question... is it true that 14CUX need "some time" to adapt fueling after resetting-disconnecting battery? Cause I've just fixed too high fuel pressure (causing overfueling) but symptoms had stayed..

Thank you so much!

Best regards

R.

Hi Rafelius,

I haven't really looked at the Roverguage any more yet. My problem hasn't cured. It came back this weekend. It still settles after a few seconds though.

In my case I can't get the engine to tick over properly on LPG once warm at traffic lights (it hunts) unless I pull off the small vacuum hose to the fuel regulator creating an air leak. I have checked my LPG setup in the LPG ECU, with the relevant software and it looks normal to me.

I suspect I have one or two lambda sensors that are on their way out or slow to respond which causes the hunting on LPG. I get an error message from the diagnostic part of the LPG software, and I have had an error on the Roverguage corresponding to the lamdba sensors.

Now my problem has come back I'll have to look at it again.

[V8david]

Thanks Nige. I have just re-disocvered this link http://www.g33.co.uk...l_injection.htm. I will do the cleaning steps in there to clean the stepper and if that doesn't work, it says what else to check and set.

Thanks.

Thanks for that. That link has some excellent close up pictures of the throttle assembly I askedfor in an earlier thread!!