Constant speed juddering woes

[Tomaxcars]

Hi

My 325i sport has been suffering with this common fault of juddering when kept at a constant speed and rpm. I seem to notice it the most when held at 40mph and 2000rpm. I also notice it when accelerating very gently up to speed.

I have replaced numerous parts as below with brand new items:
- Distributor cap
- Rotor arm
- HT leads and king lead
- Spark plugs
- AFM to Throttle body rubber boot
- Fuel filter
- Blue Temp sensor
- Air filter

Needless to say with the problem still not rectified its getting to be somewhat annoying.

The next thing on my list to check and rule out is the fuel pressure regulator.

I'm hesitant to buy a brand new one only to find that it makes no difference. I am hoping to test it as I have seen described by pinching the spill pipe. I have a few questions however

1. Does the fuel feed into the regulator and then into the injection rail?
2. Does the excess fuel then pass into the spill pipe?
3. Is this a low pressure pipe?
4. Is this the pipe that I crimp to incease the back pressure to test the regulator?

Any advice regarding this issue would be great.

Thanks

Tom

[Brianmoooore]

The alleged problem with the FPR is a small internal leak from the fuel inside it, through the diaphragm and into the vacuum pipe. Under conditions where there is an appreciable vacuum in the plenum, the connection of the FPR vacuum pipe into the plenum acts like an auxiliary carburettor, feeding extra fuel mixture into the engine.
Best test is to temporarily replace the rubber tube with a clear one.

[billgatese30]

are you sure you don't have a small air leak from between the cylinder head and the intake manifold - whats the idle like, and does it sound as if it is sucking in air from somewhere (squeaking or whistling sound)

[E30BeemerLad]

i'd agree with BillGates there

http://www.e30zone.co.uk/modules.php?na ... ing+banned

[Tomaxcars]

Hi,

Thanks a million for your replies.

I think I'm gonna check the FPR first as that was next on my list and seems simple enough to diagnose, so thanks for that Brian.

As for the cylinder head to inlet manifild, I certainly haven't noticed any whistling or squaling sounds but if the FPR doesn't prove anything then I'll move onto that.

Thanks again, your info is much appreciated.

Tom

[E30BeemerLad]

to diagnose a possible faulty inlet manifold gasket warm the car up and let it tick over (dues it hunt a bit at idle?) spray some WD40 around the manifold where it bolts to the head, if it the idle is briefly restored to smooth then that suggests the WD40 is temporarily sealing the leak.

Also check all the vacum hoses etc fit well around the throttle body.

For the price of it, it is maybe worth chucking a bottle of injector cleaner through the tank, I had a cavalier SRI about 12 years ago which had a bit of a judder when at constant light throttle, had the injectors ultrasonically cleaned and it smartened it up no end.

[Brianmoooore]

Inlet manifold to head gasket leaks aren't always audible. I had one fairly recently that I could hardly hear even when I knew exactly where it was. A sniff of propane showed it up though.
Leaking manifold gasket has the most effect at idle, and a check of all six spark plugs side by side normally shows one a slightly different colour.

[Tomaxcars]

The idle isn't that bad really. It doesn't seem to hunt so much as sometimes it periodically dips for less than a second. This causes it to feel as though its not that smooth, but it definitely doesn't hunt. The idle sits at about 600 all the time apart from these dips which don'r even register on the rev meter.

I'll do the wd40 test for sure, and I actually did a bottle of injector cleaner on my last fill.
I have a set of O rings and gaskets for the throttle body and inlet pipes so if the FPR comes up with nothing I think I'll pop off the throttle body and do a number on that to check for leaks.
From reading the link that you left on your last post it seems that the crank case breather to inlet manifld can be cause trouble if fatigued.

Its just a case of elimination, although it gets to be frustrating when everything you try doesn't eliminate the problem.

Cheers
Tom

[Morat]

Could be a lot of other things, this is a wild stab.

Does it smoke for a bit on cold starts then calm down?
Mine has knackered valve stem seals (still! fixing it this month I promise!) and it oils up its plugs. Usually no 6. If you drive on a constant throttle for too long you get a misfire. A good thrash for a few minutes soon clears it up until you get stuck in traffic again. Idle starts to sound exactly as you describe. The tiny blip is a cylinder missing.

Work your way through Brian's list before you whip the head off

[Tomaxcars]

Hi,

I see that the firefly has re-kindled the other thread relating to this problem.

Since my last posting I've done the following.

1. Checked the FPR for it sucking fuel through the diaphragm. Its isn't.

2. Crimped the return hose to improve the pressure. No difference

3. Disassembled the throttle body to gain access to the crankcase breather. I was unable to remove it due to it being held in very tightly by the O rings. I did spray around this with wd40 and the inlet manifold to cylinder head while the car was running. No change.

4. Lastly I disconnected the alternator as I know the regulator in this is faulty and causes my lights to flicker almost in rhythm with the idle rhythm. Running the car with the alternator disconnected made no difference at all.

I'm pretty much at a stage where I'm thinking of going to the main dealer to see if they can plug the car into a diagnostic machine and ascertain whats wrong. Is it likely that the on board computer or the diagnostic machine will be sophisticated enough to register the problem?

Its a non cat model so it has none of the CO2 sensors etc.

Thats the latest anyway. I hope someone finds a miracle cure for this soon.

Thanks

Tom

[fingerman]

Sorry to drag this thread up but did you get a result on this?

[DrBen]

I had a 87 325e which also had this exact problem.. Sorry to say I never solved it (I just put a 325i engine and managemant in as was always the plan anyway), but I can tell you I couldn't find an air leak with wd40, and I also replaced the FPR with a brand new one, which changed nothing. Mine had a hunt at idle, but only very occasionally, (once every ten times i drove it and only while cold) which was weird.. I considered changing the fuel pump, but it seems that was not the problem as it is fine with the new engine. Sorry I can't be of more help.

[fingerman]

Thanks for the responce - I currently have the same issue on my latest 320 I just picked up - it's bad from 40 - 60mph - juddering !

60mph and above it's okay ?

[Martinaston]

The only conclusion i've come to is its due to worn gears and bearings in the gearbox, after i'd sorted all the other bits to do with the intake and fuel side of things i still had this problem.
I think the reason it stops doing it at about 50mph is due to the wind resistance on the front of the car that stops it bouncing forwards when you apply too much throttle when trying to accelerate from a constant speed.
Stange how no one with an auto gearbox complains of this problem

[DrBen]

well I can tell you the problem I had was not the gearbox. I still have the same gearbox with a whole new engine and ecu and it's fine..

[Martinaston]

DrBen, What speed does it idle at ?

[fingerman]

Not sure the speed stops the juddering as mine does it between 40 - 65mph - and slowly driving me up the wall

It does sound like it could be a problem with air - will look more into it

[M7GHR]

I have eliminated all the things mentioned and i am now wondering if my airleak is coming from the injectors? ther is a slight smell of fuel too near the injector rail. Has anybody had problems with injectors drawing air in?
cheers Geoff

[Raj_p]

yup, i had this issue with the injectors, only very ocasionally, i could smell fuel, took it to the local garage and it turned out to be the o rings on the injectors.

[M7GHR]

Thanks, will replace them and see if it helps.

[diamondblacke28]

could be the clutch slipping slightly till it warms up

[kevin316i]

It may be more helpful to bring your car to a good independent garage that specialises in diagnostics, as there may be little or no useful information in any error codes stored in the onboard computer. Therefore solving the problem will require a very good mechanic and may take time, and the main dealers may not be the best place to find this.

[fingerman]

Just confirming - has anyone every had this problem with an auto box? - I've heard it's only with manuals?

[HairyScreech]

iv got it a little with mine, thought it was the iac but ill have to go intake hunting now.

did you do the green ones from the manafold to the block?