1994 Discovery 3.9 running/idle issue!

Morning all!!

I recently bought a 1994 Discovery 3.9i V8 auto, when i bought it i was told about the idle fluctuating...this has now turned out to be not only fluctuation but a full on issue !

When first starting cold the idle shoots up to 2k RPM then starts to settle to about 1k RPM and whilst idling ok you can feel the occasional stutter... As it warms up it gets worse and today whilst driving after first cold start it was spluttering and holding back quite badly... Also the idle is extremely lumpy and occasionally stalls. It also occasionally kicks out black smoke when pulling away.

However.... When its fully warm it occasionally will idle ok, the other times it idles low and lumpy and will cut out when put in gear.

One thing i have noticed is that the MAF sensor will make a loud whining noise which can be heard from inside, i have yet to determine wether this only happens when its idling badly, it was a brand new sensor not long before i bought the car. It has had this problem a while as I've got receipts for a new filter after it was discovered it had low fuel flow?

Does anybody have any ideas? I was thinking it could be a CTS issue? I cleaned out the air bypass valve which didn't change anything, it has new leads/plugs/cap and rotor arm, I'm gonna pop out a couple of the spark plugs to see what colour they are!

Cheers

MAF sensors are renowned to be useless unless very good quality, read: expensive.

Check it's outputs with a multimeter!

There is an actuator on the plenum that tends to get stuck and cause a bad idle

Just to update....

Its still occasionally idling like a bag of crap, however, the transition from cold to hot is ALOT worse, when started from cold it runs great, then as it warms up it gets worse and worse (backfired with big cloud of black smoke from the exhaust, stuttering etc etc) until its up to temp then its ok again, not brilliant but ok, it will occasionaly stutter if left idling.

Yesterday i took the MAF off to try on a friends range rover, forgot to put it back on mine (left it in the boot) yet i jumped in, it started and i drove off up the road like nothing was missing, it was only on the way back did i remember, upon re-fitting, it ran exactly the same as if the MAF wasnt there ?!!

Thoughts ?...... Gonna measure the Outputs tomorrow, is there a guide on how to do this ?

Cheers

have you tried a new temp sensor,(not temp sender)

Mine would start yet alone run with out maf? I have one off my disco 200 3.5 v8 if its right one and yours is broken give me a shout buddy

Would be nice to get the car on diagnostics, but failing that use the info here to check all your sensors etc:

http://www.britishv8.org/articles/rover-14cux-efi.htm

Aydena said:

Just to update....

Its still occasionally idling like a bag of crap, however, the transition from cold to hot is ALOT worse, when started from cold it runs great, then as it warms up it gets worse and worse (backfired with big cloud of black smoke from the exhaust, stuttering etc etc) until its up to temp then its ok again, not brilliant but ok, it will occasionaly stutter if left idling.

Yesterday i took the MAF off to try on a friends range rover, forgot to put it back on mine (left it in the boot) yet i jumped in, it started and i drove off up the road like nothing was missing, it was only on the way back did i remember, upon re-fitting, it ran exactly the same as if the MAF wasnt there ?!!

Thoughts ?...... Gonna measure the Outputs tomorrow, is there a guide on how to do this ?

Cheers

Click to expand...

I assume a '94 will be on cats. The ECU ignores the MAF for fuel trim and relies on the lambda sensors, so might be worth checking those while you're about it.

Oh and maybe try plugging in the MAF, unplugging the cats and fitting a non cat uk spec tune resistor.