Revs fluctuating on idle (Hunting)

[Fal_325i]

Hi Guy's

My 325i is fine on start up, but when it warms up the revs start fluctuating, I have tried in vian to locate an air leak, but all appears fine, any pointers?, When it was services the Air flow meter was checked and appeared to be fine?

Thanks
Fal

[E30BeemerLad]

Get it warmed up and then spray carb cleaner or WD40 around where the inlet manifold bolts to the head. By doing this, if there is a problem with the gaskets between the head and the manifold, the liquid will seal the leak briefly (a couple of seconds) and you may get a smooth idle restored briefly.

If it does, then you need to change your inlet manifold gaskets and also worth changing the rubber 'o' rings on the crankcase breather tube that connects to the under side of the inlet manifold

[320]

I had this problem just before i started getting oil in my air boz. Now ov been told my engines fooked. Piston rings apparently

[BenHar]

Get it warmed up and then spray carb cleaner or WD40 around where the inlet manifold bolts to the head.

I use fag lighter gas to do this.

Ben

[E30BeemerLad]

Get it warmed up and then spray carb cleaner or WD40 around where the inlet manifold bolts to the head.

I use fag lighter gas to do this.

Ben

I've always found gas effective at sealing a leak

[BenHar]

I've always found gas effective at sealing a leak

It just shows up where the leak is because the revs go up.

WD40 isn't going to permanently seal a leak!

Ben

[E30BeemerLad]

read my post, it says it will briefly seal the leak, i.e. it will diagnose the problem if the fault is with the gaskets

[BenHar]

read my post, it says it will briefly seal the leak, i.e. it will diagnose the problem if the fault is with the gaskets

I can read.

I was just offering an alternative that I have found more effective.

Ben

[BEERBOY123]

Handbags!

[BenHar]

[E30BeemerLad]

[Speedtouch]

Also try resetting the ECU. Disconnect the battery or ECU for half an hour or so and reconnect, then let it idle for at least 10 minutes to let base idle settings be learnt.

Then switch off, then restart and take it for a drive throughout the rev range.

[gnarkillius]

You can also check if the Idle Control Valve (ICV)is gunged up.

Not to mention the connections to/from the ECU from temperature and air sensors. Maybe some wrong/corrupt info being sent to the engine.

But it is probably an air leak somewhere tbh. Have you checked the oil filler cap is nice and tight, and even the dipstick can let some air in so I hear.

Also, you say youve checked the hoses, but what sort of state do they look in generally? If they are old and dried up you can get microscopic leaks, and youll only find the the leak only if you put your had in there and feel it. Make sure there are no splits under the jubilee clips, they do hide under there lol.

Since this problem comes up all the time across the range of E30s, I would like to see a good list of the things to check, in order of simplicity, or in order of likelihood of failure. Or is there one already?

SO you know, check filler cap on tight
Check condition of vacuum hoses

etc... all the way to exhaust manifold, whch I would guess is pretty much the worst case scenario. Im sure BMW had a workshop guide for all these symptoms, is there an online copy of such a thing?

I would volunteer, but I only know the checks from having the idle problem on E30s, I aint no pro.

Oh and this is always helpful..

http://www.bmwtechinfo.com/repair/main/421en/index.htm

[Billwill]

Clean the ICV valve as noted above and make sure the Throttle Position Switch (TPS) which is a small microswitch situated under the throttle is working properly. When the throttle is completely closed(at idle) you should hear the microswitch "click"....this tells the ECU you are at idle and lets the ECU adjust the ICV. If the throttle cable is too tight or the throttle backstop screw has been screwed in (supposed to be factory sealed!) then that switch cannot make and the ICV becomes useless.
You may need to measure with an Ohm-meter that the switch is working...they get oil in them and stop working!

[kman82]

Since this problem comes up all the time across the range of E30s, I would like to see a good list of the things to check, in order of simplicity, or in order of likelihood of failure. Or is there one already?

Sort of, its stickied at the top of the technical....

http://www.e30zone.net/modules.php?name ... c&t=153524

[Brianmoooore]

By any chance does this car have a lambda sensor? A failing (slow reacting) one will cause a noticeable rise and fall in idle speed