rough idle causes?

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rangerover8

New Member
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Hi folks,
i have a 3.5 efi rangerover with idle problems. The idle problems happen when engine is both hot and cold. Engine rpm will sit at 1k revs then drop to 500 then die .However it doesnt always do this sometimes it idles great (when engine is hot and has been driving) , most of the time very bad and iam not sure of the cause? Any ideas? Despite the rough idle the rangerover drives great once .

It also runs on lpg, when switched to lpg it runs and idles perfect everytime

forgot to mention, when it wont idle correctly the engine sounds ruff almost like its not getting enough fuel or something.
any help appreciated thanks...
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it had been run on lpg for a while however , before i switched to petrol i filled it up full of fresh petrol, it was on the red light when i filled it up.
 
possibly could be the throttle position sensor, but would that not affect the lpg side of things aswell? runs on lpg no problem.
 
i take it doesnt use the maf when running on gas?

do you think its diy fix? A good clean perhaps might fix it ?

keep the suggestions coming guys this is excellent , my weekend is going to busy searching for this fault now ha
 
if the maf was dodgey would this cause it to , like i said on my first post, idle correctly sometimes but most of time not idle correctly/idle ruff (spluttery)?

If the maf was dodgy would it not show a light on dash?
 
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could it not simply be clogged up injectors? i had the same thing on a p38, used redex injector treatment on it, it cured the problem within a week
 
maf only corrects the fuel/air ratio when running on petrol through ecu,lpg single point is simply igniting fuel through air induction no maf needed,blowback destroys maf on classics also check for air leaks/split pipes etc on induction & vacuum
 
Pop the plenum and ram housing off and give them a good clean. Check/set the throttle disc. Re-assemble plenum ensuring there are no air leaks.

Check all the pipework in and around the plenum, look for splits/tears/general perishing. Make sure the big pipe from the MAF to the plenum is in good order.

Clean the idle stabilisation valve AKA stepper motor.

Check/set ignition timing but be aware you need to account for the LPG.

Check/set base idle speed.
 
this morning i took the maf out , and had a look , inside it is filthy, almost like an oily residue left all over the inside of it, is this normal? What is best to clean it? just maf cleaner? will it get the oily residue out?

also what is blowback? Iam not farmiliar with this?

will also try the fuel injector cleaner, wouldnt hurt to try it.

Where can i find vacumn hoses?



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Pete The Biker said:
The stepper motor was on the 3.9 not the 3.5


Pete
Click to expand...

Not on the early flapper 3.5's but definitely on the later ones with hot wire injection although re-reading this thread this is possibly a flapper but OP doesn't say what year or injection type. Either way though, if the MAF is gunked up I would strongly recommend a thorough clean of the plenum,ram housing and throttle disc - it is really worth doing.
 
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classic kev said:
Not on the early flapper 3.5's but definitely on the later ones with hot wire injection although re-reading this thread this is possibly a flapper but OP doesn't say what year or injection type. Either way though, if the MAF is gunked up I would strongly recommend a thorough clean of the plenum,ram housing and throttle disc - it is really worth doing.
Click to expand...

Apologies Kevin, you are right!

The 3.5 had the hot wire MAF from 1988 until 1990MY when the 3.9 was introduced.

Pete
 
well, cleaned maf usuing electrical contact cleaner , let it dry out for about an hour and then installed it back into range rover, with no luck, think i have made things worse infact as lpg not as smooth as it was before.

really not sure what else would be the cause , unless the maf is completely nackered and beyond repair
 
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rangerover8 said:
well, cleaned maf usuing electrical contact cleaner , let it dry out for about an hour and then installed it back into range rover, with no luck, think i have made things worse infact as lpg not as smooth as it was before.

really not sure what else would be the cause , unless the maf is completely nackered and beyond repair
Click to expand...

Forget the air flow meter it isn't your problem!

The problem is a lack of smooth stable idle. Even with the MAF disconnected the engine should still idle, it will run extremely rich but it will still idle and run O.K. trust me on that. (If everything else is as it should be.)

Clean your plenum and ram housing!! Maybe get busy with the multimeter and check throttle pot and coolant thermistor.
 
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