Infuriating problem!

[Cloggy Saint]

This problem has been driving me insane since I've owned the car, so thirteen years! It seems to happen every 2-3 months or so, lasts between 2-4 days and then everything's ok again.
First sign of the trouble is the econometer climbs to a much higher position even though I haven't floored it or dropped a gear etc. Throttle response becomes very slow. When I come to a standstill it idles at around the 2000 mark or hunts rythmically between 500-2000 ish. As soon as I put it in gear to drive off again the revs drop to barely ticking over and there is zero power or throttle response and usually it will stall and be a complete pig to start again.
As I said, this has been going on for years and in that time I must have replaced just about everything that could be the cause of this apart from possibly the ecu (can't remember). Has anyone else had the same problem or could shed some light on it??

[Cloggy Saint]

Stupid thing was pissing around do badly tonight I ended up dumping it and walking the last couple of km. Anyone?

[Speedtouch]

Which ECU do you have? The later 0 261 200 381 type is reknowned for blowing diodes in the idle control circuit.

[Cloggy Saint]

It has a 152 ecu. The most baffling thing is the intermittent nature of the problem.

[StuBeeDoo]

Ed, I had something similar. See here I was convinced it was the ICV, but it turned-out to be the ECU. After I changed the ECU it never missed a beat until I scrapped it 9 months later. IIRC it was a 172 ECU - don't know now, though, I binned it.

HTH
Stuart.

[Cloggy Saint]

Cheers Stuart, that's encouraging. Was the problem with your car also intermittent or constant?

[StuBeeDoo]

It was intermittant, but getting more frequent. I thought, at the time, it might have been the chip but as I had a spare ECU with a suitable chip in I just used that. I never got 'round to swapping the chips to test the one in the ECU that went tits-up. When I lobbed the ECU it still had the chip in.

[Speedtouch]

The 152 is an earlier twin-PCB design of the Motronic 1.3, and they are as prone to failure as the earlier Tech 1 325i 073 ECUs.

You could try a later 172 ECU - it should be a direct swap in replacement.

[Cloggy Saint]

Cheers Maurice, I have a 172 here armed with one of your chips so I'll put it in tomorrow and hope for the best.

[Cloggy Saint]

Tried the 172 ecu and it wouldn't even fire, put the original back in and still nothing. Next plan, petrol and a match.

[Grrrmachine]

Is yours a 320i or a 325i? I've got a couple of ECUs here and can send you a standard chip to use in the 172 ECU if you need it.

When changing chips, I've sometimes found the car a nightmare to start due to the car flooding/running rich due to a lack of proper settings. So don't write off the ECU idea straight away.

[Cloggy Saint]

Cheers Grrr. The car started first turn this morning and I drove it around the block to see if it was still playing up. It was still revving high and being generally rough so I swapped the ecu and since then it's completely dead. I tried 3 different ones and it won't even fire .

[jimbom30cab]

I wonder if you have a wire that has chaffed some of the insulation away and is now shorting out ??

[Cloggy Saint]

Possible I suppose but if so it must have happened when swapping the ecu as it was at least starting before that. I'll run the usual tests at the weekend (yet again) weather permitting.

[Speedtouch]

Sounds like you may need another 152 ECU, but check the CPS first, and ensure its cable isn't worn away or internally broken - a common cause of non-starting E30s.

[Brianmoooore]

Cars with an intermittent fault that puts in an appearance every 2-3 months can be difficult to diagnose, but an engine that is dead is easy!
Just follow the standard basic checks (sparks, fuel pump activity, etc.) starting with checking (with a bulb) that there is 12 volts between the coil + terminal and earth with the ignition on.

[Cloggy Saint]

Can someone remond me which pins need bridging on the fuel pump relay base to check everything's good there?

[Cloggy Saint]

Cheers Will. Got it started today with the 172 ecu. The idle was extremely lumpy and there was a very strange smell from the exhaust!

[Speedtouch]

The idle will be lumpy at first; you need to let it idle for at least 10 minutes to enable base idle settings to be learnt, then switch off, then take it for a drive throughout the rev range.

This ensures full data transfer from the EPROM to the processor.

[HairyScreech]

As above, the ecu keeps the idle settings in a "keep alive memory" that needs power to maintain, when you swap ecus or disconnect the battery these settings are lost, thus you may find it hard to start or lumpy after an ecu swap.
The strange smell may well be a combination of damp exhaust and over rich mixture giving out stale damp petroly vapor.

Edit - I think the idle setting also have a baring on the initial throttle response as well, so if it sounds like its bogging down briefly when you initially open the throttle from idle then just persevere, it will sort its self out.

[Cloggy Saint]

Took it for a drive today and broke down twice. Whatever the problem is changing the ecu didn't help. I've just about lost patience with it now, it's one thing after the other at the moment and it's gone from being a hobby to a burden. I'm thinking of moth-balling it and getting something newer and more reliable

[Brianmoooore]

Took it for a drive today and broke down twice. Whatever the problem is changing the ecu didn't help. I've just about lost patience with it now, it's one thing after the other at the moment and it's gone from being a hobby to a burden. I'm thinking of moth-balling it and getting something newer and more reliable

NOTHING is more reliable than a sorted E30!
An intermittent fault can be difficult to sort, but you now have a semi solid fault which will be much easier. Logic will soon find it.
What does "break down" mean is this context?

[Cloggy Saint]

Same as in the first post. The petrol consumption rocketed and the throttle response was "delayed". I had to stop for some lights and the idle was around the 2000rpm mark. I went to pull away and the revs died completely. It staggered along for a few metres and then stalled and took an age to start again. Lots of grey smoke and a stinking exhaust.

[Brianmoooore]

I'd be giving the C191 plug and socket (injector connector, under the inlet manifold) a very close examination, both the pins and under the rubber boots for a start.
Has the AFM been replaced?

[Cloggy Saint]

No, still on the original AFM.

[Cloggy Saint]

Forced myself to have another look at it today and it seems better. Started first time, idled nicely and seemed ok after taking it for a short drive, but, it's spitting out a lot of damp soot from the exhaust. What does this mean??

[Speedtouch]

Sounds like it's running too rich - test the blue temp sensor resistance at the ECU plug, and try giving it a damn good thrashing.

Are you now running the 172 ECU?

[Cloggy Saint]

Yep, fitted the 172 last weekend and let it idle for 10 minutes and then took it for a drive but it was very rough and still over-fuelling. Today was the first time I've been back to it since then.

[Speedtouch]

Does it have the standard chip in it?

[Cloggy Saint]

It has one of your mild chips.

[Speedtouch]

Well, it should be OK. Do you have a standard chip to try instead?

[Cloggy Saint]

Digging up this old one again . Twice in the last week it developed the same problem again but this time just for about an hour. Both times it started fine in the morning and ran with no problems but after going back to it when the engine was still just about warm it struggled to idle and had zero throttle response. After about 10 minutes of this it slowly started to respond with much missing and popping until after just letting it do it's own thing it eventually sorted it's self out. Any further suggestions?

[Brianmoooore]

I'd be giving the C191 plug and socket (injector connector, under the inlet manifold) a very close examination, both the pins and under the rubber boots for a start.

Had this lot apart yet?

[Grrrmachine]

Sounds like it's running too rich - test the blue temp sensor resistance at the ECU plug

This was from September. Has it been checked? As Brian states, if the C191 is rotten/corroded, then the blue temp signal won't get through to the ECU and your car will run rich.