M20B25 high idle / over fuelling

[FinalD]

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Right, it failed on emissions before with a horrific 6.78% CO, since then I've changed the blue temp sensor, cleaned the ICV, and TPS. I've also replaced the fuel tank and but brand new fuel in.

It is running at over 1k rpm at idle and producing smoke that smells of petrol, this says to me it is putting too much fuel in. I need to sort this before Thurs morning (so tonight or Weds night) else I suspect I'll fail another MOT, if it fails again I won't be able to work on it for a few months.

I've read the wiki about the blue sensor, the ICV and the TPS hence replacing and cleaning. Any more ideas? The only other thing that I've seen mentioned that could result in this is dicky injectors if that is the culprit, the car is staying in the garage for the foreseeable and I can't sell the Mondeo.


E: The idle does fluxuate a little but it doesn't seem to dip below 1k that often. I'm fairly sure it was idling at around 800rpm when it went in for the test before.

[Grrrmachine]

I've read the wiki about the blue sensor, the ICV and the TPS hence replacing and cleaning.

No mentioning of you testing the blue sensor or its wiring to the ECU, which is the most critical aspect.

[FinalD]

I mentioned that I replaced the sensor.

How do I test the wiring, and if the wiring has failed, how do I replace that? I do not have time on my side for this at all, if that'll take more than an hour or two of work the car is just going to have to be stored.

E: nvm, multimeter on the ECU's plug.

[Grrrmachine]

Replacing and testing are two completely different things.

http://www.e30zone.net/e30zonewiki/inde ... ug#Testing

[FinalD]

Tested the sensor and wiring with a crap meter, pretty much the same at both the sensor and the ECU plug, as I expected. Having replaced the sensor I'm fairly sure I can rule out that being the problem so running to warm would be excessive.

[Grrrmachine]

If those are the results then you're ok there. But it's an essential check because the C191 plug rots away.

Next thing may be the AFM - if that's unplugged then the engine will overfuel because it doesn't know how much air is going in. You'll also need to ensure that the TPS is set up properly, but even then they do fail. Trouble is, you really need a replacement and you haven't got time by the sound of it.

Don't think it would be the injectors though. They've have to be jammed open to give that sort of issue.

[FinalD]

I have spare AFM, ICV and TPS from the dead engine, luckily they aren't a pig to change over (well, the TPS is a bit). I can't really guarantee any of those work 100% though either which doesn't help.

I had the ICV and TPS off and cleaned both with carb cleaner, the donor engine ones (fitted) were clean and the old ones were full of yuk (old engine spat mayo back out the throttle body). TPS had oil in it (not much, just a minor film and the ICV looked grim) but as I say, those aren't used, the clean ones were used.

AFM - I have two, both are clean and I'm not sure if they make any difference, I'll test it with the spare and see if it there is any change.

[Grrrmachine]

TPS is one of those funny units that can make a "click" that sounds like it works, but you really need to put a multimeter across it to confirm. You just need to make sure that when it clicks it changes its resistance (usually from infinite to zero, or vice versa).

Try that, try swapping the AFM, and don't forget to let the engine idle for ten minutes. I know that the ECU needs to relearn its settings if its been left disconnected for a while, but never to the point where it overfuels like what you're experiencing.

[FinalD]

Changed the AFM over, idles high, BUT (and I didn't test this with the other AFM), if I blip the throttle a little (take it to ~1500rpm from ~1100rpm) it drops back to ~800rpm and then creeps up to ~1100rpm and stays there again.

That says TPS or ICV then surely? It isn't able to realise that it will stay idling at 800 so creeps it up. ICV does make it's lovely (read: horrible ) whine pre-ignition so it is at least partly working.

Ideally I'd like to avoid running it in case the over fuelling causes any internal problems (read some stuff about bore wash with over fuelling), but I'll let it idle for 10mins or so if need be.

I guess multimeter on the TPS pins? Is that a throttle body off test (I know access isn't nice), or can I make it click and test whilst all on the engine?

E: http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

I should check before asking.

Simple enough then, can check in situ with no power to it?

[FinalD]

Tested the spare, 1 & 2 read, then don't when open. 1 & 3 don't seem to?

Tried testing the fitted one (hard to get my eyes and hands in under the intake boot), no reading when closed, I'll remove the currently fitted one and see if I get bad results when I have proper access to it. I'll also check the spare one again when open.

The screws holding the spare in look like they are made of cheese, so I may need to replace the throttle body as a whole which means I need to really clean up the inside of the spare one due to oil and mayo.

[Grrrmachine]

I feel your pain testing the one that's fitted. I found it easier to swap it with a known working one to rule out the issue.

You just need to ensure that the TPS is sending an Idle signal to the ECU. At the moment, it sounds like it isn't. I don't know whether it's possible to disconnect the plug to the TPS and bridge pins 1 and 2 with a wire, and see if the car settles at 800rpm idle. Of course, if you blip the throttle at that point the car will probably stall.

[FinalD]

Right, that ended up being a little more complicated than I'd have liked but, I think that is the idle sorted.

The screws holding the TPS onto the dirty TB were hard to remove without rounding but doable, the ones on the nice TB...well, a screwdriver can't undo them now!

What I have done is swap the two TBs over (after cleaning up the spare) so it has a working TPS. Car now idles but splutters/doesn't pick up straight away when the throttle is opened. I can only assume this is then pins 1 & 3 sending a bad signal?

It's cold and dark and the idle is sorted (~800rpm idle) so I'm stopping tonight.
I can't test my idle CO emissions pre-test as I don't have a CO meter. The exhaust doesn't stink of fuel though so I can only assume/hope that the levels are much better. I only put 5L of fuel into the empty (as in bone dry new) tank earlier so tomorrow when I get back from work I'll dump another 5-10L in and take it for a spin down our private track, see how it drives. I think it'll stall when I try to move it due to it not picking up quite right when you apply a small amount of throttle. If it seems dangerous then I'll have to buy a new TPS and it'll have to wait to be put on the road.

[Grrrmachine]

If the sensors have been duff, it might make sense to reset the ECU before you go for a drive. From cold, undo the battery, link the two wires together for a minute, then refit and restart the car. Let it idle for 10 mins, then turn it off. Restart, and go for a thrashing drive.

If your "new" TPS switches from 0 to infinity as soon as the pedal is pressed then that's all you really need. The setting at the other end is WOT, which basically tells the ECU "ALL GUNS AT ONCE!" and chucks fuel out of every injector. Not necessary for MOT, I think.

[FinalD]

Hahaha, yeah, I'd hope they don't WOT it for the MOT. As the car is pre 1991 and doesn't have a catalytic converter the only engine test is the emissions at idle, so provided I've sorted that, there are no issues.

I'll reset the ECU tomorrow and idle, I can't legally take it for a thrashing drive though as that requires MOT, Tax and insurance. I only have insurance, I'll probably take the 'long way' to the MOT station on Thursday morning though. ;)

[FinalD]

Did the ECU reset, couldn't really thrash it but I did kind of set the rears spinning on the private track (1/4 mile gravel track) and snaked my way up it.

Seems to be running ok, idle is fine, stops, goes etc. and doesn't appear to be smoking at idle, it is cold out though so the exhaust gases are condensing when leaving the car/garage, it is also dark, so hard to tell. Early start tomorrow and I'll take it for a good thrash to the MOT station and see how it runs. Fingers crossed this has sorted the fuelling.

[Grrrmachine]

Good to hear you've got the idle sorted. If you're really worried about the MOT, make sure the engine is properly hot before you arrive, so that it's still not in its rich-running warm-up mode.

[FinalD]

Yeah, that is what I plan on doing, taking a detour and emptying the fuel tank.