My Classic starts first time, Runs very well on road for about 5/10 minutes then starts running very rough including backfiring lumpy as hell. After I pull over the engine ticks over over fairly well. If you blip the throttle it really doesn't like it, very uneven running. Eventually it clears and engine runs very well.

I stop for a while and the engine cools down then it is slow to start and the running rough starts all over again untill it totally warms up. Any suggestion? I am looking at the automatic choke because this sort of fits with the engine getting up to temperature then problem starting.

Which Air Flow Meter and ECU does it have?

fallers said:

I am looking at the automatic choke because this sort of fits with the engine getting up to temperature then problem starting.

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There isn't an 'automatic choke' on an EFI.
There is a cold start injector (sometimes know as the ninth injector) in the driver's side of the plenum, but this will only activate whilst the starter is cranking & that's assuming it's connected in the first place .. I'm never found the device necessary during ownership of four EFI RRC's.
I believe the ECU adjusts the firing duration of the 8 injectors when the engine is cold, taking that info. from the coolant temperature.

If I read your reply correctly then the 9 th. Injector only works while cranking, so that could not be the problem I have? But the temperature sensor that gives information to the ECU could be the problem? Is it the same sensor that supplies information to the Dashboard temperature gauge? (Which seems to work OK) or is there another sensor somewhere else that needs replacing?

Not being a mechanic, just a long term owner of these Classics, I'm not the best person to ask but I do know that the sensor in question is not the same as that which serves the gauge.
There is a wealth of experience on this forum, others will be along to offer more explicate advice.

Please confirm which AFM & ECU combination you've got.
Given it's a 3.5EFi I'm expecting it to be a flapper AFM & a 4CU ECU but conversion to the later hotwire isn't unusual.
The flapper AFM is item 14 in this link: Lrcat

The associated 4CU ECU has something of a reputation & the only way to check is substitution with a known good one.
That can be problematic.
They do come up on ebay but the prices can be eyewatering & you can't guarantee that what you receive will be any good.
Also used in the Rover SD1 3500 & can have several part numbers. I emailed Lucas some years ago & their advice was that they are interchangeable & that's been my experience on my own RR.
However, IME if an ECU develops a fault it doesn't come & go so hopefully the issue isn't your ECU

IF your inlet manifold is as in this link then the sensor norseman is referring to is item 15 (ETC8496) often described as 'the one behind the easy one' & should be replaced.
There used to be a repairers that had the website carelect.demon but that seems to have disappeared & their advice was that in the event of rough running that should be replaced as a matter of course.
Lrcat

The sensor that does the dash gauge is in the front of the inlet manifold. Item 12 Lrcat

The ninth injector - on the side of the plenum, item 12 in this link Lrcat - serves no useful purpose in the UK & can be disabled by unplugging the electrical connector. Which I did on mine shortly after I got it in 1994.

Yours PROBABLY won't have a stepper motor - item 20 & associated bits in the same link - but as Range Rovers are 'Big Boy's Meccano kits' it's best not to assume anything.

The factory workshop manual contains a lot of testing instructions & you really need to follow these.
AFAIAA there is no online manual for these RRC with that EFi setup although there are sites which may have pictures of the pages of the paper manual. I have no idea if any of the online .pdf downloads work or are suitable.
The later factory RAVE CD doesn't cover it.
The factory manual is a thick paper book 'Range Rover All petrol and diesel models 1986 to 1989' ISBN number 9781855204430. They do turn up on ebay from time to time. Not cheap, got mine new years ago from Brooklands Books & IIRC it was £50 ish, but has saved me a fortune over the years. Can't find it on Brooklands website - I've just looked.

ETA. Check all the plenum hoses are tight & in good condition. If any of them can allow unmetered air in - air that hasn't passed through the AFM - then it will throw the whole system into chaos & the ECU won't be able to sort the fuelling. I had the extra air valve hose split on mine - item 8 Lrcat - & the car was very rough.

Carelect are still repairing ECU'S but they are now based in the Isle of Wight.

locket said:

Carelect are still repairing ECU'S but they are now based in the Isle of White.

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Thanks.
This one? COMMON ECU FAILURES ON RANGE ROVER, CITROEN, MITSUBISHI AND OTHER EUROPEAN AND ASIAN CARS. (avilec.co.uk)

Ratea
I'm surprised at the advice from Lucas regarding the interchangeability of the ECU's as the power/torque requirements for the two engine variants would be totally different, but I won't dispute it.
Your advice to the OP is very comprehensive & should be of considerable assistance.

Must admit I was. But I had several 4CUs with different part number stickers on & that was what they came up with.
It also went against this, who say they did notice a difference: Rover SD1 Efi Electronic Control Unit (ECU) (vintagemodelairplane.com)
Lot of info on that site. Should keep you amused for hours

Ratae said:

Must admit I was. But I had several 4CUs with different part number stickers on & that was what they came up with.
It also went against this, who say they did notice a difference: Rover SD1 Efi Electronic Control Unit (ECU) (vintagemodelairplane.com)
Lot of info on that site. Should keep you amused for hours

Click to expand...

I'll look forward to being amused, thank you R

Ratae said:

Thanks.
This one? COMMON ECU FAILURES ON RANGE ROVER, CITROEN, MITSUBISHI AND OTHER EUROPEAN AND ASIAN CARS. (avilec.co.uk)

Click to expand...

Yes

Ratae said:

Must admit I was. But I had several 4CUs with different part number stickers on & that was what they came up with.
It also went against this, who say they did notice a difference: Rover SD1 Efi Electronic Control Unit (ECU) (vintagemodelairplane.com)
Lot of info on that site. Should keep you amused for hours

Click to expand...

You were right

fallers said:

My Classic starts first time, Runs very well on road for about 5/10 minutes then starts running very rough including backfiring lumpy as hell. After I pull over the engine ticks over over fairly well. If you blip the throttle it really doesn't like it, very uneven running. Eventually it clears and engine runs very well.

I stop for a while and the engine cools down then it is slow to start and the running rough starts all over again untill it totally warms up. Any suggestion? I am looking at the automatic choke because this sort of fits with the engine getting up to temperature then problem starting.

Click to expand...

Could be as simple as a blocked crankcase breather assuming you have fitted the correct spark plugs, plus leads & coil and the connectors are OK. Then you can think about testing or replacing the EFI engine temp sensor.

I had a similar issue on my 1987 3.5 just after two years of ownership and in the end the engine but would start again, so took it back into my main dealer for its annual service and mentioned my issue, although rocker cover flame trap isn’t listed as a service item the service department replace it.
Anyway, as the flame trap was only item to be added to the bill for the basic fluid change service so I could only take at the time that was the cause of my issue.

But 6 or so years later the issue returned, so I fitted a new flame trap and washed the hose in petrol, instantaneously the engine wasback to normal, and still no issues when sold in1997.
The old flame trap was cleaned in petrol and place on the shelf, just incase my disco had a stalling issue, but it never has although now 25 years old, but then spin off the flame trap wash it and refit when I feel like it usually at an oil change.

As for the RR 9th injector on the 3.5 EFI the only information at the time was a guess, no forums then, just a main dealer RR owners club, it was intended just in case the vehicle went into the northern hemisphere where winters are cold, out of interest I did eventually readwhat the the ambient starting temperature would be for the injector to function… so a long while ago… but could have been somethinglike - 25c

I was always suggest as the reason for the the 3.5 difficulty in starting, even when the owner stated the electrical connection was unplugged… so not much different from some forums now.

Don't discount the ignition amp aso. This is known to breakdown when it gets hot causing a weak spark/no spark and lumpy running, struggle to start issues until it cools down and all is well again.

The early EFis had the amp under the coil on the l/h inner wing.
Later ones had it mounted on the side of the dizzy & affected by heat to the extent that LR came up with a kit to remotely mount it.

Thanks to every one who has replied offering solutions and possible remedies.
All HT Leads are good Qualiy, As is Distributor Cap, All hoses have been checked a
and are OK. The 9th injector is disconnected, Vacumn advance on distributor changed. Static timing checked and is OK, All readings from the Air Flow Meter Connector are just as they should be, Have this morning changed the ECU. Temperature Sensor. Net result! Nothing has changed.

Next stop is to change the ECU for a known good one.

Rotor arm of the moulded in strip variety & not the riveted on strip type?
This style: Lucas 35D V8 Rotor Arm Red with Powermax Technology (simonbbc.com)
Not this type: MGB V8 ROTOR ARM GRA2133 (mgbhive.co.uk)
Although I'd be inclined to think you'd have a misfire all the time if it was faulty.

The check is to take the dizzy cap off & hold the end of the king lead (HT lead, coil to distributor) just above the centre of the rotor arm & crank the engine. Use suitable protection to avoid shock. No spark should jump the gap.

Ratae said:

The early EFis had the amp under the coil on the l/h inner wing.
Later ones had it mounted on the side of the dizzy & affected by heat to the extent that LR came up with a kit to remotely mount it.

Click to expand...

Even back then LR were making minor changes as they go along.

The early did indeed have the coil clamped on top of an ECU with an amplifier because the distributor used then still had contract breaker point's.
Then later distributor was fitted had a magnetic sensor and after that LR moved the amplifier to the side of the distributor… that was 1987 with the ‘face lift, model, thats I purchased my 3.5 RR and which never had any overheating issues with the amplifier in the 10 and a bit years I had it

But I did have a major issue with the EFI ECU, (starting from cold in the morning and have having thick blace smoke from the exhaust).
That was when the main dealers did have any ECUs in stock and LR I was told as it was a batch fault on ECU for my model year. but now the 3.9 was in the showrooms. So Lucas parts were getting short.
The dealer’s method in fault finding was to swap the ECU from a similar RR that was in their work shop for repair, and then found that my RR didn’t have a problem, so paid the dealer what ever and took my RR home and sort it my self.

So I removed the ECU and took it to a Lucas factory near Burton on Trent and handed in to the service dept, within a few hours they handed it back to me with replaced and new and updated components and I handed over £100, Then another fast drive returning to Kent… fitted the ECU and started the RR instantly better than it ever did.

And when my the 3.9 disco (300 series) was introduced LR placed the amp together with the coil on the engine bay slam panel behind the near side headlamp.