Technical Rough Idle

[Chiddleston]

My panda 1.2 Mylife has developed a rough idle. Sounding and feeling like it wants to cut out but doesn't, the idle rpm drop below 650. Connected an obdii to it and shows no error codes. I replaced the spark plugs, ht leads and gave the throttle body a clean which all helped a bit. Now it is still rough(not as bad as before) but rpm slowly builds up to normal followed by a dip in rpm then jumps to normal idle, mostly with a cold engine. The throttle body doesn't seem to have an idle control valve in it, just the butterfly flap and no obvious air bypass valve. Any ideas where else that would be? or other things I could check myself before handing it over to a garage?

thanks

 

[koalar]

Could be anything unfortunately. As of yet we haven’t got enough information to do anything but guess just about everything

The latter engines don’t have an idle control valve. The butterfly is controlled by the engine computer

Let’s see if we can narrow down the guess work a little for you

Apart from the idle are there any other symptoms (poor acceleration for example)

Does the car judder when pulling away


Gave the throttle body a clean. Why was it covered in gunk (black or mayo)


Post a photo of your old spark plugs

Does your code reader have a live data function

If you stand by the exhaust at the back can you hear a regular tutting noise

Have you checked the state of the MAP sensor

 

[koalar]

For some strange reason these engines don’t idle correctly if the battery is faulty even if the alternator is pumping out 14.1V and the car turning over okay

If you have a volt or multi meter if it measures over 12.4V after the car been stood overnight it’s fine

 

[Chiddleston]

The car accelerates really good, and drives smooth with no juddering. Better than its been for a long while. MPG is slightly better than before but probably down to new plugs
Added Injection cleaner and petrol system cleaner, on separate occasions
starting from cold the revs drop and rise between 690 to 790, same when warm but sounds rougher. sometimes it drops to the point the engine rattles and tries to cut out then seems to run normally after.
Exhaust sounds a little deep when its warming up just making 'goldfish popping' noise. doesn't sound like backfire or misfire.
Binned the old plugs, they were worn out evenly anyway all showing similar marks on tips, no physical damage just wear
Throttle body wasn't overly filthy and cleaned up OK, the recess the rubber seal sits in on top of the manifold was full of crud and oil though
Had the MAP sensor off it looks in good condition, and clean. was a little oil on it that wiped off
had a 40 mile drive yesterday and it cut out once, almost at the end of the drive.
Still no error codes or pending errors
Cant hear any hissing from vacuum pipes
Didnt notice anything out of the ordinary on OBD except RPM fluctuating up and down at idle and the exhaust/fuel still showing on closed loop even when fully warmed up. Is it feasable the cat or a O2 sensor failure can cause the rough idle?

Thanks

 

[gforce1]

My guess would be a vacuum leak. Check all the hoses for splits.

 

[koalar]

My guess would be a vacuum leak. Check all the hoses for splits.

There aren’t any vacuum hoses on these cars. Unlike cars that run a map sensor

The airbox is bolted directly to the throttle body. If you remove the air box and leave the two breather tubes off these engines run just fine

Any small leak pre MAP sensor and is automatically adjusted for. The only problem we have ever seen is between the cylinder head and the plastic inlet manifold when the engine has badly overheated

 

[koalar]

The car accelerates really good, and drives smooth with no juddering.

Good

Better than its been for a long while. MPG is slightly better than before but probably down to new plugs

To be expected with good plugs vs worn out

Added Injection cleaner and petrol system cleaner, on separate occasions
starting from cold the revs drop and rise between 690 to 790, same when warm but sounds rougher. sometimes it drops to the point the engine rattles and tries to cut out then seems to run normally after.

Rattling will be the engine running on two cylinders

Exhaust sounds a little deep when its warming up just making 'goldfish popping' noise. doesn't sound like backfire or misfire.

Popping noise sound like one ore more cylinders aren’t firing properly

Binned the old plugs, they were worn out evenly anyway all showing similar marks on tips, no physical damage just wear

Shame as they can tell a lot about how the engine is running, lean, oil and so on

Throttle body wasn't overly filthy and cleaned up OK, the recess the rubber seal sits in on top of the manifold was full of crud and oil though

Wet around here is not a good sign. See below

Had the MAP sensor off it looks in good condition, and clean. was a little oil on it that wiped off

Not correct. The little oil on it is because something is wrong. Blocked breather pipe is likely. I don’t like saying this but head gasket is another likely cause

had a 40 mile drive yesterday and it cut out once, almost at the end of the drive.
Still no error codes or pending errors
Cant hear any hissing from vacuum pipes

1.2 shouldn’t have any vacuum pipes. If you mean the two crank breather the car should run fine even if they are disconnected

Didnt notice anything out of the ordinary on OBD except RPM fluctuating up and down at idle and the exhaust/fuel still showing on closed loop even when fully warmed up. Is it feasable the cat or a O2 sensor failure can cause the rough idle?

Possibly

Does your scan tool read fuel trims

If so what’s it read engine warm and at idle


If it’s plus a lot at idle and goes to more normal at 2000 revs then it’s not firing properly at low revs

 

[Chiddleston]

Notice today when starting engine from cold with obd attached the fuel system is Open loop, a few seconds later before temp gauge even moves it goes into closed loop and starts idling rough

 

[koalar]

Notice today when starting engine from cold with obd attached the fuel system is Open loop, a few seconds later before temp gauge even moves it goes into closed loop and starts idling rough

As expected as soon as the o2 sensors detect the Unburnt fuel it messes up the fuelling

It should go into closed loop as soon as the o2 sensors have warmed up about 30 seconds

 

[Chiddleston]

It was more like 3 or 4 seconds then switch to close loop. I'll try take a look at fuel trim tomorow

 

[koalar]

I’d probably start by pulling the injector electrical connectors off one at a time and starting the car and see which ones make the least difference when listening from the back

Here’s the fuel trims of a 1.2 with low compression on cylinders 1 and 2. Not a great photo as the engine isn’t running I seem to have deleted most of the other photos on my phone


Also a video of a working 1.2. Hot engine left to settle at idle for about a minute. Ignore the scale look at the steadyish voltage on the post O2

 

[Chiddleston]

BIt of an update. Seems it was the large breather hose from under the air box to the intake manifold bypassing the throttle body that had become blocked as it was full of debris and covered in cracks and small splits. Cleared it and the plastic tube it connects to in the manifold and put a load of temporary tape around it. 24 hours later car was in for MOT and sailed through with better emission results than last year and no advisories. Engine was splutterey on and off for a couple more days but 10 days and 200 miles later the problem seems to have cleared.

 

[atakan123123]

View attachment 411441

I wonder what software is this?
It looks very useful

 

[koalar]

I wonder what software is this?
It looks very useful

I use both delphi DS150E and WoW with a multiplexer, they are both very similar and connect to any module ABS, EPS, BSI, Dash and so on without having to change any cables, both are very expensive.

Works on most makes and models from 1988 onward

Has some cool features such as you can put an SD card in and use it like a flight recorder and mark when certain triggers are met

You can also command the abs pump to operate so you only need to open each bleed screw to do the brake including flushing the abs unit out


But for general engine related problems I use torque lte and a £5 Bluetooth dongle