325i Pulsing/Erratic idle issue but drives fine

[jarques325]

Brian previously gave me advise on how to get my E30 going and thankfully it runs and drives, however the idle seems to bounce from 1000 rpm to 1500 rpm rather quickly, I'd say 95% of the time. The other 5% it idles at about 600rpm. I would say that first 5% seems to be when started, this high or pulsing idle seems to be after a few minutes of running. It is a new idle air control valve as I automatically assume it might be playing up.
Just wondered what else control the idle that I am missing?

[HJ1981]

Normally a high idle means a vacuum leak, but this is not always the case.

Did you check all hoses visually? have access to make your own smoke machine/tool?

How is the TPS? the original one on my 325i was not creating continuity at WOT (or 90% near WOT) and everytime i slammed my foot on the pedal, it got a violent fuel cut off (took me a while to check everything).

We shall look at the fueling system one you eliminated vacuum leaks.

[jarques325]

Hi, thanks for the reply, no nothing on the vacuum front, everything looks fine, it starts fine and initially idles fine then after about 2-3 minutes the idle picks up to 1000 then will keep pulsing from 1500 rpm to 1000 rpm every second, so I suppose it fluctuates between 1000 and 1500 and doesn't not drop down to normal revs,
Is it odd that unplugging the IAC valve does not change the mad idle??

[Brianmoooore]

Are you saying that the idle continuous to fluctuate between 1000 and 1500 RPM with the idle valve disconnected electrically?

[jarques325]

Yes that's right mate, makes no difference in the revs, it keeps doing its 1000 too 1500 rpm but only after a few minutes from start, initially she idles beautifully,

[jarques325]

Is it best if I try and get a video posted? I have been a reading a few posts on fuel pressure, could this be a potential for my idling or not really?

[Brianmoooore]

In order to turn over at any particular speed under no load, an engine needs a certain amount of air. If the ICV is unplugged at normal idle revs., and then it begins to act up afterwards, then it must be getting the extra air from somewhere.
Highly unlikely to be anything to do with fuel pressure.

[jarques325]

1) What should I eliminate as a cause, if the TPS is shut, ie no throttle request and the IAC is unplugged, assuming then it has a default opening, then where can air enter to cause revs to fluctuate so precise?
2) Does the ECU use the Coolant temp reading and other loads to the engine to control opening of the IAC valve?

[Brianmoooore]

The three wire ICV used on the M20 should stay put at the opening it is at when unplugged. It is effectively two electric motors opposing each other, with no return spring.
The ECU uses the (blue) coolant sensor to slightly increase the idle value stored in the ECU's software until the engine is partly up to temperature. After that, all the idle control part of the ECU does is compare the engine revs. with the stored value (760 RPM), and if the former is higher than the latter it increases power to the ICV 'close' motor, or, if the former is lower than the latter, it increase power to the ICV 'open' motor.
Any extra air that's getting in must be after the throttle butterfly to increase the idle speed. ir getting in before the butterfly will upset the fuel mixture, which can only reduce idle, although with the ICV connected overshoot can occur.

[jarques325]

Thanks for the reply, the bit that puzzles me is that on initial start up she runs perfectly, now my thinking is if it is an air leak then why does it not affect the idle then, could I be missing something?

[Brianmoooore]

It does affect the idle - its speed. Air leaks after the throttle affect the speed. Air leaks before the throttle, but after the AFM affect the idle quality.
I forgot to add to my last post that you should probably check the resistance of the blue temp. sensor AT THE ECU PLUG with the engine stone cold and at full working temperature before getting too involved with chasing air leaks. Check between pin 45 of the ECU plug and a good body earth.

[jarques325]

I didn't get a chance to check pin location today but I did quickly disconnected the CT sensor (Blue) just to see if the ECU will run on its pre saved default and it did change the running. Check engine light stayed off and pulsing running stopped. It started from cold idling at 500 rpm and as the car heated up revs went to 1000. It didn't seem to go over the 1000 but equally I know that is too high, bit I am pleased the puling between 1500 and 1000 stopped.
I will replace the CT sensor soon and see what that does to the revs.

[Brianmoooore]

It was important that you didn't disturb the temp sensor, or anything anywhere near it. You may have disturbed an intermittent fault. That's why you should have measured the resistance at the ECU plug, so that you can discover for sure whether anything actually is amiss with the circuit before turning your attention to the individual parts and wiring.
Don't replace anything without determining whether or not it is faulty.
Having said that, it does look likely that something in this area is at fault, although the results you obtained aren't exactly what should have happened. The engine should have started from cold and run almost normally at around 800 RPM, before being to run increasingly badly with a very lumpy idle.

[jarques325]

Brian hopefully you get to see this, this morning after reconnecting the battery (as I though the car will not be used for the week) I unlocked the door and turn the ignition at which point all the doors locked themselves and the car turns over but wont start, I did get back out unlocked the doors and tried again but no it turns over and sounds like it wants to start but doesn't, almost like it has no fuel. My assumption is that the factory alarm is activated from connecting the battery? It does have the door tumbler type alarm for which I don't have the key, any suggestions?

[Brianmoooore]

If you look through any reply I've made to a thread involving disconnecting the battery (usually chasing a current drain), one of the first things I advise is to fully open the driver's door window, in case the alarm/immobiliser/locking activates when the battery is connected. Not all do, but some will.
If you need to get the car running, just run a wire from the battery + terminal to the + terminal of the ignition coil (don't remove the wire already connected). It's that easy to bypass the standard BMW immobilisers!
All alarm/immobilisers were dealer fitted, so it's impossible to be certain how they are wired in, since occasionally a dealer's technician would do his own thing, and ignore BMW' instructions, but your immobiliser connection should be at a two pin socket with two plain green wires going to it, fairly high up behind the glove box. Cars left the factory with a plug in this socket which had a short loop of green wire connecting the two pins together, but, if an immobiliser is fitted, the plug should have one plain green wire and a green/red wire connected, with the wires disappearing to the right.
To disable the immobiliser, look for the plug with the loop of wire tied up to the loom nearby, or if it's not there, cut the green and green/red a couple of inches from the plug and join them together to form a loop.

[jarques325]

H mate, thanks again for the reply, you previously pointed me towards the Green wire loop when I was trying to get it started and yes mine was blank so just plugged in a Green wire loop I found online and that did get it started and it run until this morning. So currently mine has the loop fitted. All I did was connect the battery, turned the ignition and suddenly all the doors locked and now she wont start. The key set up on the drivers door, what do they do or how does it work, any clues? I have read previous posts and there seems to be a module in the drivers side under the speaker that can get water in, not sure if that could add to mu issue

[Brianmoooore]

Tried this yet?

If you need to get the car running, just run a wire from the battery + terminal to the + terminal of the ignition coil (don't remove the wire already connected). It's that easy to bypass the standard BMW immobilisers!

Module in the sill will lock the doors and burn out the motors if flooded, but won't affect the engine started.(don't underseal over the drain slots!!)

[jarques325]

I'm still at work, I will be doing it in the morning if it doesn't rain. Thanks though.
What could have caused the doors to lock when I turned the ignition? It has never done that before.

[HJ1981]

I'm still at work, I will be doing it in the morning if it doesn't rain. Thanks though.
What could have caused the doors to lock when I turned the ignition? It has never done that before.

That is how my CLS started to go crazy, ignition on and everything was locking and unlocking uncontrollably till the system stopped working. Still did not find the time to check what is the case yet.

[jarques325]

Hi Brian or anyone looking, changed the fuel pump as I thought it is too old and wanted to make sure most components are replaced and the old pump kept blowing fuse 11, so did that but the car still wont start now, the fuel pump relay has no earth, pin 85 which has 2 wires too it, I think Brown with a Green tracer. When I earth pin 85 the fuel pump comes on as it should, according to what I can find the ECU provides that earth, is that right? Also why the 2 wires on pin 85 of the relay? Surely they cant both go to the ECU?
My question is where does those wires go?
Also the revs are still high when the engine is on operating temperature, it seems to do the pulsing thing less but revs are still not below 1000rpm,

[Brianmoooore]

The ECU only earths the brown/green wire from the fuel pump relay when it senses the engine is rotating. It decides the engine is rotating when it see pulses from the crank position sensor. The pulses from the sensor are also processed to provide the trigger pulses for the ignition coil, so check to see if you have sparks at the plugs when the engine is cranked.
I've never seen a second brown/green connected to the relay that I know of on any post facelift 325i, just a single wire that goes directly to the ECU, so I can't help you there.
I've just had a quick look back through the thread and I can't see what age this car is?

[jarques325]

Hi mate, thanks again for your reply. How you know all this is beyond me.
Yes on crank I have an earth and yes she runs and drives fine, even the temp gauge works but I feel its temperamental.
I still have this strange running but what it seems to do lately is at some points t wont do it, more so when it is hot, but again no hard and fast rule, its very intermitted when it will run that way,
I have a video of it running like this if it might help. Are there any engine tuners out there that I can take it to?
The fact that my one use to be an auto, could there be any connection with regards to my issue?

[martauto]

A video may help someone point you in the right direction.

Mart.

[jarques325]

Thanks for the replies, I have video but unable to upload, any suggestions?

[Foe]

Thanks for the replies, I have video but unable to upload, any suggestions?

Try uploading the video to you tube, then link the video on here.