I've got a lumpy tickover. I've had cambelt done and changed spark plugs. I'm not sure that it was doing this before or not as I had only driven it to the paint shop and back. It drives fine and the lumpyness is less when the engine is warm.

It's also sometimes taking two turns of the key to start it.

No errors anywhere on the dash or on MES.

Readings on MES on the engine while it's running show that the pre-cat lambda has a closed loop and the post cat has an open loop. This has been like this at cold start and when normal running temperature.

Knock sensor also shows 0.0V. Would this be right?

System is shown rich on both Lambda's in the attached picture but this was just after starting. Now it's at temperature, pre-cat is showing lean but post cat is showing rich. Am I right in thinking this isn't right?

Would appreciate any help.

Surely you can't have lean pre cat and rich post? "Could" point to post cat lambda?

That's really what I'm hoping. I got my new project today so immediately plugged it in the same and that shows the post cat as "Active" rather than lean or rich.

The open circuit shows too, so that's obviously a thing.

OK, so I've tried a few things. MoT garage confirmed it's "missing".

So as I have an identical car (model not colour), I've been swapping some bits around.

I put the old plugs back in - tried it - the same

I swapped over the coil pack - tried it - the same

I swapped over the pre-cat Lambda - tried it - the same

I can't get the post cat lambda undone unfortunately so unable to try that but does anyone think that this could be down to a tooth out cambelt. The cambelt was changed before this happened. I don't think it was like it beforehand. There are still no errors being thrown up or codes stored by MES so I'm at a bit of a loss as to the cause.

Got someone coming to look at the car today too. Luckily they know it's like it, so are not expecting it to be ready to go. Very annoying.

So so far as well as what’s been mentioned, I.e. coil pack, plugs, leads and now both oxygen sensors, my mobile mechanic has been back today and redone the cambelt.

It’s still lumpy on tickover.

Air leak somewhere?

Update

I have so far changed, plugs, leads, coil pack, both lambda sensors, MAP sensor, cam sensor, fuel rail wiring, fuel rail and injectors. Still exactly the same. Cambelt has been taken off and redone and is spot on.

Someone has suggested it could be a sticking valve. I have ordered a bottle of injector/valve cleaner and a bottle of cataclean.

There’s pretty much nothing left to change. Stumped!

Compression test each cylinder .
Compare results.
Any one cylinder lower reading than others?

Check valve clearances.
Perhaps one valve being held slightly open?

Best wishes

typecastboy said:

Readings on MES on the engine while it's running show that the pre-cat lambda has a closed loop and the post cat has an open loop. This has been like this at cold start and when normal running temperature.

System is shown rich on both Lambda's in the attached picture but this was just after starting. Now it's at temperature, pre-cat is showing lean but post cat is showing rich. Am I right in thinking this isn't right?

Would appreciate any help.

Click to expand...

Sorry I'm coming to this thread late, just read it, Home life is quite hectic just now, not got much spare time to come on here!

Regarding your O2 sensor values. The values shown when on open loop are of no great interest in this case. Once she's warmed up (I like to go for about a 5 mile drive so not just water but oil and everything else is properly heat saturated) I would be graphing the sensor outputs. So, as you may know? to graph the Pre Cat sensor output, click to tick the box in the Pre Cat sensor value you are showing in your illustration and then go to the top menu and click "Graph". The sensor output will now be displayed in real time and it should be switching between about 0.1 volts to 0.9 volts cycling around one to two times per second. The absolute values may not be quite as I state so say 0.2 to 0.8 would certainly be acceptable. Now lift the revs to about 2,500 and you should see the frequency increase - ie, it should switch faster, more times per second. A poor sensor will give lower output values and/or is likely to be slower switching.

The post cat sensor value can be read in the same way but now you will expect to see a more or less constant output if the Cat is doing it's job properly. A high reading (rich if you like) is not unusual if you have a good Cat. This is because the O2 sensor is looking for oxygen. If the Cat is working well it will be using any free (unburnt) oxygen in the exhaust gasses to help converting residual gasses to Carbon Dioxide and water. So, because the sensor sees little oxygen it sends a high (rich) signal and the graphed line is straight because the Cat is removing mixture fluctuations which the pre cat sensor is subject to.

This video has been sited by a couple of Forum members and it illustrates what I'm talking about really well:

https://www.youtube.com/watch?v=rWIpwNI3cAU&t=190s

So, long story short, Pre Cat sensor output should oscillate between around 0.1 and 0.9 volts with a frequency at tickover of around once to twice per second, getting faster with increased engine revs. Post Cat sensor should be straight line - although you might just induce a bit of a "blip" if you give the throttle a vigorous "stab" and a high voltage (tending towards the 0.9 volts) might be expected if the Cat is fully up to temperature and in good working order.

Hope that helps at least a little?

Anyone interested in pre cat O2 sensor diagnostics? I found another of this chap's videos to be very helpful:
https://www.youtube.com/watch?v=xswml0muJsw&t=322s

Thanks for that, very interesting. As I've now changed both sensors I think it sort of rules them out now. I've literally changed everything and it's not made a blind bit of difference. My last hope is the injector/valve cleaner.

Throttle body needing a clean all through may. E unlikely to cause a misfire


Other possible thing could be a ECU fault which would be a pain to find

When it's showing "rich" on closed loop on the Pre Cat O2 on diagnostics, it actually means the engine is running lean and it's adding fuel to trim it out.

The Post Cat readings are a bit stranger as it's output/readings change as the Cat heats and cools and as it's never likely to be tested at the same temp twice, you never get a reliable figure to compare.

My boys Panda is doing the same thing, running a little lumpy at idle and it had a small issue at MOT last week getting the Lambda to drop enough, we stuffed a rag up the exhaust to kill off some of the excess oxygen in the exhaust and the reading dropped enough to pass.

I suspect there's a small air leak somewhere (I know the small stub on the breather under the airbox is broken).
They didn't spot an exhaust leak, which is another common reason for excess oxygen in the exhaust.

Before I took it in I did notice a lot of sooty carbon around the bleed hole on the exhaust, so I suspect it's been doing it for a while.

Just reading up on some other lumpy idle issues and discovered a few problems with manifold studs.
https://www.fiatforum.com/500/450207-slight-idle-problem.html

Goudrons said:

Just reading up on some other lumpy idle issues and discovered a few problems with manifold studs.

https://www.fiatforum.com/500/450207-slight-idle-problem.html

Click to expand...

I’ve just read that but the difference being my revs aren’t going up and down, they are static but lumpy tickover.

It’s weird. If I drive it, it’s fine. When I park or pull over, it’s fine for a second or two then starts the lumpyness.

Not an idle control issue ?

What rpm is this lumpy idle??

The boys Panda is doing the same, it idles a steady rpm but it's a bit heavy and lumpy (typically rich) rather than erratic, up and down idle (typically lean).

There's also a fair bit of soot around the tailpipe which shows it's rich.

Going off the the mot test, CO2 and HC's were ok, just the Lambda was a little high, it didn't take much effort to bring it down with a rag.

It's idle isn't bouncing around all over the place like you get with an air leak on the intake side and the CO2 and HC's are within spec.

Without the bouncing idle I suspect all's ok with the air entering the engine, it's just adding extra fuel.

So my thinking is it's running rich, but it's not rich because it's trying to trimming out extra air entering the intake side. They usually fail at that which is why the bounce.

HC's and CO2 are within spec but the Lambda's high. (stuffing it with a rag and it coming back is typical of an exhaust leak)
I'm not getting a EML, so whatever it's doing, it sort of does it normally and it's unable to identify a problem.

These all point to something post combustion screwing with the O2, so there must be an exhaust leak somewhere.

I didn't get anything back from the MOT on an exhaust leak, so I guess it's small but close to the pre cat O2 sensor to mess it up.

I haven't looked at the car yet, but I reckon it's either the manifold (gasket, stud, crack?) or perhaps the flexi pipe.

varesecrazy said:

Not an idle control issue ?



What rpm is this lumpy idle??

Click to expand...

Normal 800 ish

Goudrons said:

The boys Panda is doing the same, it idles a steady rpm but it's a bit heavy and lumpy (typically rich) rather than erratic, up and down idle (typically lean).

There's also a fair bit of soot around the tailpipe which shows it's rich.

Going off the the mot test, CO2 and HC's were ok, just the Lambda was a little high, it didn't take much effort to bring it down with a rag.

It's idle isn't bouncing around all over the place like you get with an air leak on the intake side and the CO2 and HC's are within spec.

Without the bouncing idle I suspect all's ok with the air entering the engine, it's just adding extra fuel.

So my thinking is it's running rich, but it's not rich because it's trying to trimming out extra air entering the intake side. They usually fail at that which is why the bounce.

HC's and CO2 are within spec but the Lambda's high. (stuffing it with a rag and it coming back is typical of an exhaust leak)
I'm not getting a EML, so whatever it's doing, it sort of does it normally and it's unable to identify a problem.

These all point to something post combustion screwing with the O2, so there must be an exhaust leak somewhere.

I didn't get anything back from the MOT on an exhaust leak, so I guess it's small but close to the pre cat O2 sensor to mess it up.

I haven't looked at the car yet, but I reckon it's either the manifold (gasket, stud, crack?) or perhaps the flexi pipe.

Click to expand...

Sounds like grief but mine sounds very similar to yours.

typecastboy said:

Sounds like grief but mine sounds very similar to yours.

Click to expand...

I've only ever suffered twice from a similar problem before with a Panda.

The first I had a rough idle and lumpy (heavy) running on our old 169 1.1 Active, it was a very odd one as it sort of cleared it's self after a restart.

There was obviously something going on with the Open Loop, cold start fueling, but because restarting it warm caused it to go straight into Closed Loop it took me quite a few attempts and a lot of waiting around with my ODB dongle to crack what was going on!

Something was causing the fuel system to trip into a funny "Open Loop System Fault" soon after a cold start, a sort of emergency fueling strategy.
It just wouldn't trip into Closed Loop from a cold start no matter how hot it got, it would only trip into Closed after a hot restart.

There wasn't any codes, just this rough idle/running after a cold start.

I took both O2's out (they were the same) and fired up the heaters direct from a battery, then wafted a blow torch on them with a multimeter connected to see how they reacted.

They both worked, but the front one was a bit lazy to react. It needed more heat to get anywhere near 0.9v out of it.

I reckoned it's heater element was on it's way out so I swapped the O2's over and it ran like a dream again.


The second was because of a cheap replacement silencer I fitted.
It ran all wonky and lumpy after the replacement and when I logged the O2 is was obvious it was struggling to fuel properly.

I noticed the exhaust took time to expel the gases after a rev up, it went on for a while.
I reved it up, walked around the back and the exhaust fluttered and putted gas for a good few minutes afterwards rather than settling down quickly.

Seemed like the cheap Eurocarparts silencer wasn't passing the gases fast enough and choked up the engine and O2.
Fitted a new genuine back box and it was back to it's happy self again.

Both the above were lumpy/heavy/rich idle and running problems and not the bouncing hot/lean running issues you get with an air imbalance entering the engine.

They were actually fueling imbalances which are generally due to post combustion problems and it seems I'm getting similar symptoms with the Boy's Panda now, so when I get my hands on it, that's where I'm going to look.