Oxygen/lambda Sensors- Which Cars Had/have Them?

[worzel]

Hi

As a newcomer I don't think I can add/input anything useful and if I seem to be asking questions the answer to which might seem b*******g obvious I apologise.

Sorry- here's another one but first some background info.

In Jan this year I bought a really nice 91 525i auto. Inevitably though I met a few problems- mainly concerned with low speed running.

Symptoms- coming to a dead stop, once up to normal running temp inevitably the engine would be surging between about 600-800 revs for a few seconds then settle down until the next stop.

Cold starts- no problem and no other issues during warm up.

Additionally- if in slow moving traffic and just using idle speed to inch forward the surging would recur.

What I've done- the simplest things first-

Change plugs, air filter, fuel filter. Drained/flushed gearbox and changed filter.

Fitted new TPS

Fitted new Bosch MAF after original was diagnosed as having an intermittent internal short

Fitted a (reportedly) known working Bosch ICV

Result- clearly improved- surging when stopping pretty much cured with only occasional surging when crawling in traffic.

However (always an however) I notice that occasionally during warm up when engaging drive depressing the throttle induces a momentary jerk that feels like the engine is trying to stall. Once at normal temp this doesn't occur.

Thinking it might be an idea to change the oxygen sensor (as I suspected it might be linked to the problem of surging when hot when the O2 sensor kicks in) I booked it in to the MoT station I've used for the past 15 years or so. Good garage, knowledgeable sensible staff so definitely not cowboys.

Here's my question- they informed me that actually it doesn't have an oxygen sensor fitted and it appears never to have had one. There are no loose wires/cut wires etc and as he said if somebody had just deleted the sensor you'd expect this to show up as a fault code.

So- can anybody confirm that it's possible that a Feb 1991 car might well not have been fitted with one of these?

Regrds and thanks

John

[Guest DazH]

I had a 1991 525i Manual which indeed had NO Lambda sensors. I have the engine from that car in my '87 right now so yes, definatly none :P

Daz

[worzel]

Hi Daz

Thanks for that useful bit of info.

I recall that when I recently had the inlet manifold off the car I noticed that there was a plug not being used. On the basis of where the Bentley manual identifies the usual location of the sensor (by the starter/under it) I'm guessing that on my car there was provision for one in the original specification but it wasn't fitted.

Does that sound a reasonable assumption?

Regards

John

[worzel]

Hi-again

Following on from Daz's reply- am I correct in thinking that cats became compulsory in the UK post 1992 and-

I'm getting confusing messages on this- the Bentley manual indicates that the revs shouldn't drop when engaging a gear but I've read posts from other owners who report that this isn't so.

Bentley do suggest that a fall-off in revs might indicate problems with the ICV/ICV wiring circuit- which is correct/

Incidentally, since accessing the ICV is such a pain as I previously mentioned I've relocated it next to the throttle body and it does seem,as somebody pointed out, the orientation of the valve is irrelevant to its operation (mine sits vertically rather than sideways). Makes replacement a 10 minute job at most although not quite as neat as BMW would prefer.

Regards

John

[Guest DazH]

Yea I believe you may have posted about the orientated of it in the past and I replied with... "it doesn't matter"

You'll see an o2 sensor pocking out of the actual exhaust manifold if you have any. IF you DO NOT have any; there will be bolts visible blocking the holes. If you DO, you'll see them..

[Guest Mister Dabsy]

This is a "classic" example of intake air leak where the revs fluctuate...

Causes? Imperfect seals on the hoses

- cracks in the above...

- shite filter

Call me a "guesser" but if the Idle control valve and throttle body haven't had a clean etc etc

;)

[worzel]

Hi Mr D

Thanks for reply. I agree that air leaks are pretty common but I'm pretty sure there aren't any in this case- here's why-

Every hose on the intake system has been removed and pressure tested- I've replaced some that were marginal

The servo pick up hose has been replaced as a precaution and the servo is holding vacuum

The throttle body has been removed and cleaned/ditto the idle valve

All the above I did myself so I'm not taking another's word that they've been completed.

plus- when I removed the inlet manifold (for the second time) I relocated the idle control valve so it sits right next to the throttle body (for convenience) I modified the hose system for this using new silicone hoses with the pick up that clips under the manifold properly fitted with silicon instant gasket. Additionally, I'm now venting the head breather direct to atmosphere (rather than into the intake system) and I've blanked off where these hoses normally feed into the engine. In effect the only air feeding into the engine comes through the filter and MAF plus any going thru the idle valve. The pick up for the fuel pressure valve has also been properly silconed into place.

I admit to little experience of fuel injected cars with this number of intake hoses and sensors but I do have a lot of experience with twin double choke sidedraught dellorto carburettors which in themselves are fairly complex devices and (my experience only) I've found that air leaks and the symptoms they cause at slow running speeds tend to be present (and sometimes worse) when engines are cold- unless the air leak is being caused by something expanding as the engine heats up.

However, I take your point so as a double check my next job will be to spray carb cleaner over all hose joints whilst the engine is hot to see if the revs alter- I'll report back.

Regards and thanks

John

[worzel]

Hi and premature seasonal greetings!

Can report I eventually fixed the idling fault- now it no longer surges. Field lane service station (long established independents for BMW) suggested a few simple fixes (I admit to being sceptical about their offerings)- but seems to have worked-

Advice was-

Only use premium grade juice- apparently these cars don't relish the supermarket stuff

Switch the box into sport (I haven't tried this as I haven't needed to).

Run it for about a 100 miles or so on the better fuel.

Seems to have worked.

Two last points-

As I was told, relocating the icv next to the throttle body hasn't affected its operation so thanks for that info and a question-

Should the revs drop when engaging drive- the Bentley bible says no but what do others think. Revs drop only slightly but I suppose it would make sense if they were unaltered or even rose as on modern autos.

Any offerings?

Regards

John