idling probs M40

[Alyman]

Hi folks

After my car's untimely exit from the Scotland meet, it's been off the road while I try to fix its problems.

It turned out the scary noise the car was making was due to it having cracked a downpipe all the way round, just below the manifold, most likely due to a dodgy engine mount. Had the exhaust replaced but the engine is still running rough as hell, starts fine then after a few seconds the revs drop so low that it almost stalls, then they go back up and the cycle repeats itself.

I've had a read through lots of old posts on idling problems, and these are the things I've done so far:

1. Swapped the idle control valve with a spare one from my old engine.
2. Checked to make sure that my TPS goes "click" when the throttle is fully released. it does.
3. Replaced my blue temp sensor....must say i was a bit surprised that when it came out it was bone dry? Maybe a stoopid question, but shouldn't it be reading the temp of a liquid? Radiator level looks good, but maybe there's an air lock? Would that explain my problems?

Failing that, what's my next step? Fuel pump/filter?

Hope someone can help, I usually drive my E30 for a living....while it's off the road I've been having to drive the company car......a Toyota Yaris with dents in every panel and a driver's window that goes down but not up again

[Chris-W]

Intake rubber ok?

[Alyman]

Yup the intake rubber looks fine, no splits

[codell]

i got the same problem, pretty much replaced what you have so far, would be interesting to find out. Have you checked your timing?????? thats next on my list

[Chris-W]

Does it behave well on the move, under load?

[Alyman]

drives fine, its just at idle that it all goes wrong

[320Touring]

Hmm, Glad It was just a cracked manifold afterall.

Have you checked the Plug gaps?

[Alyman]

nope, not checked that yet

wee project for tomorrow then, cheers for the input

off to work now....in the Yaris

[codell]

book it in for a diagnostic test?? see what that comes up with, have you checked your fuel pump and regulator?

[bmwe30mtech]

I had this for almost a year, did all the stuff you have, and it still wouldnt idle. In the end I just adjusted the screw on the top of the bulkhead to increase the revs.

Im told you not supposed to do this, but after a year i got fed up, and the car runs perfectly now. Anyway its the wrong thing to do apparently, but worked perfectly on mine.......

HTH

[codell]

can you show us a pick of the screw you adjusted so we know which one it is?

[Chris-W]

I presume it's the throttle cable stop.

[jon316]

Have you had the CO reading checked at all? The mixture might be off. You can mess about with this using the screw on the side of the airflow meter on top of the airbox. there's a screw hidden under an anti-tamper cover. The idle on my 316i went funny after changing the exhaust from a straight through to a stock one and also after switching the standard air filter for a K&N. The revs would wander all over the place when it was cold and throttle response was delayed quite a bit. A couple of clicks on the CO adjustment screw on the side sorted it out. You need to adjust it when the engine is up to operating temperature and do it little by little - I didn't have a CO meter, I just guesstimated. Might be worth taking it to a garage if you value doing things properly though

[jonbuoy]

DON'T PLAY WITH SCREW'S!!!!!

They are set up right in the first place!

The problem you have got is an air leak, find that before doing anything else.

Adjusting screw's at guesstimate's will make your engine over fuel.....badly!!

[Alyman]

Well, as I'm fairly sure that my engine overfuels already, I'll be leaving that screw alone for the time being!

Where are good places to check for air leaks? I've read about people finding a random vaccum hose lying about in the engine bay and then sticking a bung in that...can't say I've ever seen it flapping about but I'll have a closer look today.

Where else should I be looking?

And since no-one has mentioned it, I take it that the fact my blue temp sensor was dry when it came out is not a problem....?

[E30Mark]

And since no-one has mentioned it, I take it that the fact my blue temp sensor was dry when it came out is not a problem....?

That is a big problem! have you got any water in the engine???

[Alyman]

See, I knew that sensor should have been reading a liquid!

The radiator is topped up to the normal level, and the temp gage normally gives a good reading, dead on halfway aferr it warms up. I'll flush all the coolant out and make sure there's not an air lock.

Thanks Mark, I was starting to think I was being silly about that sensor!!!

[Jonny_71]

Where are good places to check for air leaks? I've read about people finding a random vaccum hose lying about in the engine bay and then sticking a bung in that...can't say I've ever seen it flapping about but I'll have a closer look today.

Check the big rubber air inlet very carefully as they can look fine, like mine did, but actually be cracked between the 'folds' on the bend. There should also be a thin vacuum hose running from the fuel pressure regulator into the throttle body. Check that your ICV is properly seated in the inlet manifold, and also check the rubber hose running from the ICV back to the main rubber air inlet. Then there's the vacuum hose from the brake servo...... The list goes on. and on.....

[Alyman]

Just been down having a rummage around the bay, tightening up jubilee clips etc - had a good look at the intake rubber, its in really good nick...

Started looking for that mystery vaccum hose that some threads said should be lying around... didn't find it, but i did notice this:





its a wire coming out from under the manifold, it splits in two with one wire connected to the box on top of the air filter housing and the other connector, as you can see, is swinging about freely connected to nothing. Where is this suopposed to go? I can't see anything for it to connect to!

[Jonny_71]

Ah, the mysterious 'extra connector', don't worry, it's not meant to be plugged into anything. Can't actually remember what it's for. Some type of accessory-type gizmo thingy?

[Alyman]

Ah, so it's not the answer to my prayers then...

i did kind of remember that extra wire from the engine swap, but as everything started up fine without it I just forgot about it... for a wee second i thought it had come back to haunt me!

[jonbuoy]

There is a vacumm pipe there, exactly where your photo's are.

The blue temp sender is doing it's job, it read's the temp of the water. As you know, water evaperate's so that would be the reason it was dry.
If you have a problem with the running temp then you may have an air lock but don't fix what don't need fixing

Have you had the inlet manifold apart for any reason?
Is the original pressure regulator still attached?
Why do you think the engine is over fueling?

[bigdek]

poss inlet manifold gasket

let it idle and spray around the inlet manifold joints with carb cleaner or wd 40 .

If there is a leak the spray will seal it momenterily and your idle should change for a sec or 2.

Had this prob on my sport

[Alyman]

I'm totally starting to lose the plot with my car. Down in the sideways rain this morning, working in my wind tunnel/carpark, managed to shear off one of my rocker cover bolts while tightening it had to stop myself getting a hammer and trashing the damn thing.

Went back up to the flat and sulked for a while, when the weather finally got a bit nicer I headed back down and tried the WD40 thing, without any result... I'd like to check that i was concentrating on the right areas though, my technical term vocabulary is quite rubbish - when you say the inlet manifold joints, do you mean the bits that i have arrowed in the picture below?



Cheers

[bigdek]

well there as well but where it bolts onto the head

[geo1400]

I've done 3 rocker cover bolts so far and only 2 have been saved. If the gaskets good and the rest of the bolts are ok then you shouldn't loose any oil or pressure. I've been driving around for 10,000 miles with 7 working bolts.

I had idling probs and after a ICV sorted part of the problem I had the inlet manifold gasket done, worked wonders!

Hope you sort it. And don't go

[Alyman]

Well, I spent a good while down at the car, spraying WD40 around all the gaskets etc without any effect, so I finally decided to stump up some cash and took the car down to the Edinburgh Car Tuning Clinic for a diagnostic test.

Got a full report on the engine and all its components and the verdict is that it's an inlet manifold gasket, blown between cyliders 1 and 2 (so no leak to the outside which would explain why the WD40 trick wouldn't work for finding it.).

There is still a slight chance that it might be the head gasket, I'll only know once I've changed the manifold gasket over...

Fingers crossed!

[SGP]

Surely the tempsensor should be immersed in a solid stream of liquid.Coolant should pour out of the thermostat housing when the sensor is removed.The engine will be overfuelling 'coz the ecu is getting a cold reading from the sensor and it will never run properly.lol.

[Brianmoooore]

Just been down having a rummage around the bay, tightening up jubilee clips etc - had a good look at the intake rubber, its in really good nick...

Started looking for that mystery vaccum hose that some threads said should be lying around... didn't find it, but i did notice this:





its a wire coming out from under the manifold, it splits in two with one wire connected to the box on top of the air filter housing and the other connector, as you can see, is swinging about freely connected to nothing. Where is this suopposed to go? I can't see anything for it to connect to!

This plug is for the solenoid valve for a charcoal cannister for the fuel tank vent. The blocked up hose hanging off the inlet manifold is also part of this system.

[Brianmoooore]

Surely the tempsensor should be immersed in a solid stream of liquid.Coolant should pour out of the thermostat housing when the sensor is removed.The engine will be overfuelling 'coz the ecu is getting a cold reading from the sensor and it will never run properly.lol.

There's only two possible reasons for the sensor to be dry: 1/ there's no water in the engine, or 2/ There's so much sludge in there that the sensor element is in a pocket of the stuff.
Suggest you take the sensor out and have a poke around with a piece of stiff wire through the hole.

[Alyman]

Cheers mate, I'll do that when I've got the manifold off to replace the gasket (for once the blue sensor will be easy to get to! )

[Alyman]

I'm back on the road!

I changed all 3 inlet manifol gaskets, found that spare vacuum hose and blocked it off, flushed the coolant out and refilled with new stuff. Turned the key and the engine sounded better but the idle was still hunting about a bit. Took the car back down to the Car Clinic for my free retest to see if the air leak had been solved - it had, but the engine was still running way too rich. Got them to tune the car using their fancy gadgetry, got my emissions down from 1500ppm (MOT fail) to a much healthier 200ppm.

And she now purrs like a kitten, idles at a steady 800rpm or so!

Cheers to everyone for the help