Anyone got a degree in sorting out poor idle?

[AlpineCab]

This is not the usual "clean the ICV out" issue, and this post is also a bit long, so thanks for reading it, and hope you can help!

My M20 2LT runs great on the go, starts on the button, but the idle needs sorting.

When, and only when, it has warmed up, it just keeps hunting up and down, by +/- 200rpm every second, and the hunting is regular as clockwork.

So far, I have done all the usual things and I service the car regularly using OEM stuff.

It makes no difference whether it has been driven for 5 mins or 2 hours.

All I can think of now are:

A. "the connector that joins the main engine loom and injector loom(sits under the tb)" referred to in another post - is there any merit in this?

B. Could the non standard exhaust be causing this? It's a one-off stainless steel item, and I wonder if that could be causing the exhaust gases to pulse, and so cause the engine to choke itself a bit at idle? Or is that being a bit over analytic?

C. In the relay tray, aside form the standard relays, there is a much bigger relay-thingy, what does this do - could this be the trouble maker?


I AM PULLING MY HAIR OUT AND NEED ANSWERS!!!!!

Can anyone please Help?


Things I've done so far are:

1. All connections (that I can find / know of) have been cleaned with proper stuff from Maplins - great start and made the engine run much more smoothly.

2. Temp sensors (blue / brown) replaced - no difference noticed.

3. All air pipe work has been replaced and re-checked for seals, original bellows was split.

4. Valve clearences have been done.

5. Exhaust manifold gasket has been done.

6. All relays replaced - funnily enough, this did make the engine pull quicker. Perhaps this was all in the head? but I'm not so sure...

7. New air flow metre - big improvement.

8. New ICV - unbelievable improvement in the overall smoothness of the engine whilst on the move, and much smoother when you lift off the throttle.

[Brianmoooore]

You haven't mentioned the throttle position switch under the throttle body.
Doesn't have a cat/lambda sensor does it?
Worth checking out the injector plug, and giving it some of your electrical cleaner in any case.

[AlpineCab]

Hi Brianmoooore - What do you mean by the injector plug?

As to the other points, yeah, I forgot, I did put a new TPS and replaced the gaskets between throttle and inlet manifold, with no difference whatsover noticed.

And, Yes! you're right, this is a cat ready engine, but there is no actual cat / lambda sensor there.

[Brianmoooore]

Injector plug is the one you mention in your OP - the one below the inlet manifold.
You've changed the TPS - And adjusted it correctly?
I mentioned lambda sensor, because a varying idle like this is typical of a failing lambda sensor, but if one isn't fitted.....

[AlpineCab]

TPS - yes, I think so, it clicks just when you open the throttle, and I have also checked the thing with a multimeter. There was a good how-to in one of the BMW mags.

So where exactly do I find the injector plug, cos I had a look under the throttle body and can't see anything. Is it a standard type plug similar to the others (e.g. the one that plugs into the temp sensors?)? What am I looking for????

Cheers.

[Brianmoooore]

So where exactly do I find the injector plug, cos I had a look under the throttle body and can't see anything. Is it a standard type plug similar to the others (e.g. the one that plugs into the temp sensors?)? What am I looking for????

Cheers.

Round black plug and socket about 30mm diameter under the manifold fitted through a hole in the black metal plate that holds the pipes and cables.

[Jon_Bmw]

A. "the connector that joins the main engine loom and injector loom(sits under the tb)" referred to in another post - is there any merit in this?

This is the connector that Brian is refering to, the one you've quoted from another thread. Twist off the cap from underneath, and pull out the plug. Not sure what you've got to do with it then, but clean it comes to mind.

[Dan318-is]

alpine cab

how much u pay for airflow sensor, temp sender and ICV,

i need to replace these also

[AlpineCab]

Brianmoooore / Jon_Bmw - Cheers, I'll have a look and see what I can find.

Can I post again Brianmoooore if I get stuck with this? Not usually so inept its just that I can't seem to find this plug....

318-is - I got these all new. Now, I'm all in favour of used parts, and have bought stuff from the zone, but for these items I wanted as much a guarantee as poss. of them working cos I'm determined to sort out this prob. and to be honsest they all improved things greatly.

Airflow (dealer) was Ԛ£150ish

Temp sender (dealer) was Ԛ£5ish

ICV (was from GSF) and was around Ԛ£80.

[Jos]

My head could be full of sweetie mice, my M40 does this, although not 200rpm, only about 50rpm or so variation, someone told me it could be a sign of a tired cambelt?

See above for the sweetie mice...

[Dan318-is]

cheers fella

[AlpineCab]

Cam belt's been done...........

[gareth]

does it get significantly worse when you remove the oil filler cap? mine was very lumpy and had lost its rubber seal so was drawing huge amounts of air in though the crankcase and then breathers. new cap cured it... purely by chance that i found it!

[TheDutch]

Did you check the injector o-rings? There is a good chance they are fine, but there is a possibility that they are perished and no longer providing a good seal to the intake manifold.

Speaking of which, have you replaced the intake mainfold gaskets? I did mine last week which has at last cured my hunting idle. If you've not you may first like to try simply re-torquing the nuts as my gaskets showed no visible damage and doing this may have been sufficient if they had just worked loose.

Neil

[AlpineCab]

Update----

Brianmoooore / Jon_Bmw
Have checked the connection between the injector and main loom. Round black connection that unscrews in the same way as the diagnostic socket?

Strut brace prevented me reaching it fully from above - couldn't get hands down to it - but superficial clean up improved things no end!!!!!!!!!! I'm going to have to do this again properly from the underside as you suggest of the engine so I can get a good reach.

Engine now idles smoother, no hunting as such, ie fixed on circa 700 rpm.

But still got a choking / stuttering, to the extent that the whole car is juddering...... But idle is steady rpm now!


gareth
Yes, this is the case cos it's effectively introducing an air leak into the engine? I out on a new oil cap cos of that.

TheDutch
Injector o-rings? are they easy to reach? Retorquin the inlet manifold seems a good idea - just the sort of zero cost tune up technique I like to do!

To be honest, the reason I'm really doing all obsessive detective work is because I want to rule out anything else before I look at injectors or inlet gasket which are my two main suspects (and costly!).

Cheers for all your suggestions chaps!!!!!

[AlpineCab]

Another Question ------

Is the electrical connection between the injector loom and the actual injectors themselves easy to get to and clean?

What do I need to dismantle?

[Dan318-is]

inlet gasket only cost 6 quid m8 lol

and the throttle body gaskets 1.62

pieece of piss to take them off tho

[TheDutch]

Replacing injectors is costly, but rebuilding intake with new gaskets should not cost the earth. On my iS there were 4 gaskets altogether thanks to BMWs mucking about with extra bits and bobs, but there could be just 3 or 2 to do on yours. Mine came to about Ԛ£14 from BMW.

Either way, if you do remove the injectors be VERY careful of the plastic tips. If they are anything like mine they will be incredibly easy to damage (just the plastic shroud at the end), but they will also love the idea of being cleaned as mine were chocked full of grime.

note : don't believe eveything the internet tells you, I followed a guide to replace o-rings which suggested I exert a 'suprising amount of force' to remove the tip. I did this, only to find my tip was now in a surprising number of pieces

There is bags more info on the procedure if you look, let me know if you need assistance.

N

[E30BeemerLad]

an easy way to determine the inlet gasket etc is to spray wd40 around where the manifold bolts to the head with the car running, if idle alters then you've not got a proper seal

[AlpineCab]

Cheers TheDutch

[AlpineCab]

Hi E30BeemerLad, I'll give that a go as well, after I've tightedend (carefully) the nuts on the manifold.