Not the normal K11 throttle body problem...

Hi all,

Just bought a 52 plate 1.0 K11 for the other half to learn to drive in. Needs a bit of TLC so I'm slowly working through it fixing problems. It has a bit of an idle issue - once the car is warmed up, when you take your foot off the throttle it bogs down quite a lot before returning to the normal idle speed. So when pulling up to a roundabout or traffic lights for example, the revs drop to around 300rpm for a second or so before pulling back up to 800/900. It never actually stalls but it feels like it's going to (car starts to shake, lights dim etc). Otherwise the car drives well and is happy through the rev range. It may be a bit gutless at the top end but it's only a 1.0! Engine warning light works and is not lit. This is what I've done so far:

Check water temp sensor via OBD - warms up correctly
Check O2 functionality via OBD - lambda reports constant fluctuation above and below 1V as normal
Alternator and battery voltage are good, even with air con on and electric windows in use
Clean throttle body and IACV
Replaced MAF with genuine Bosch item

This is a very late spec K11 with coil packs and the updated type of throttle body so it's not just a case of popping the cover off and soldering the connections or replacing the waxstat, and there are no idle screws to adjust.

I think that either the IACV is knackered or 'lazy' so it's opening slowly. That's my next port of call. However i don't know if the ECU is realising it's duff and pulling the ignition timing which is why the problem only exists for a second... How can i easily diagnose the IACV? If i unplug the connector I would expect the car to stall and if I take the IACV off the throttle body it will leave a big hole and the idle revs will be through the roof. I've noticed the TPS reads 7.2% open when the throttle body is closed - is that normal? I've had cars before that have only activated the IACV when the TPS reads 0% but they had 4 pin TPS with an idle microswitch and the Micra has a 3 pin sensor so it must calculate when the throttle plate is closed differently. The throttle cable is slack at idle so it's not being held slightly open.

Any other suggestions? How can I easily check the mechanical timing and ignition timing? After the IACV, TPS and timing I'm at a bit of a loss...

Sorry for the essay!
 
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OP
OP
toxo
I've not properly tested it from cold startup yet but I'm gonna tentatively say that I've fixed this by cleaning up and reseating the connection to the O2 sensor. I set my OBD tool graphing all of the sensors it could read from the ECU (not very many compared to modern cars!) and noticed that fuel trim was way way off when coming off the throttle, it vanished down to virtually 0 which wasn't inline with what the timing advance was doing at all. I figured that fuel trim is governed by the O2 sensor so fiddled with it and it now all seems to work.
 
OP
OP
toxo
Have you checked to make sure there are no vacuum leaks my k11 had that issue when i forgot to put a breather pipe back on

Yeah I have. The intake path on the later bosch intake is really short and the brake booster and carbon canister hoses are bolted on so you can't really get them wrong. That only leaves 2 breather hoses and they are both fine!
 
Have a different issue my self, but as you have been investigating obd live data, you might be able to tell me whether you are obtaining speed reading pid data.

I have a log file that I believe may be beneficial as a comparison. But as I have a different issue I thought best worn you.
And explain the issue so you can decide if it is going to be of any use to you.

The issue I'm having is p0500 which is not consistent. Every thing seems normal after cleared, and doesn't seem to effect running if and when generated.
If I drive car I can get it to thow fault code. But if mum does then it occasionally throws code. So have logged it.
 
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