Lumpy when hot

[Swanny]

I took my faithful Matilda up to Carlisle at the weekend; 300 miles of angry driving after getting lost was fun but I noticed a rather lumpy idle when I started engine after stopping at services.
Fine when driving, but sounded almost like it was missing a cylinder when idling. I restarted it 3 or 4 times and it eventually sorted itself out. I've seen this before, only when hot it seems. Has anyone had anything similar? ICV perhaps? Runs fine when cold (as fine as can be expected). Fitted new plugs, dizzy, rotor and leads a couple of weeks ago but hasn't fixed this.

Cheers.

[Rachel]

Engine temp sensor, or the connections on the sensor??

[eye of ra]

I have just spent over a year trying to sort out my idle which at first was doing the same. Over time the temperature at which it would start got lower and lower to the point it would do it from cold and the times it would correct itself got fewer and fewer.

Like you I changed the plugs, dizzy, rotor and leads I also changed the engine temp, fly wheel, air pressure and knock sensors, the ICV, ignition coil and ECU and maybe some other things I’ve forgotten about, all to no avail.

It turned out to be a vacuum leak from the gasket on the throttle body which had been rotted away by oil coming in from the crankcase ventilation system.

With the throttle body removed to change the gasket getting a rubber mallet in to remove the oil trap and clean it was much easier (having tried to remove it before and failing).

I now have a perfectly idling 480 and a clean oil trap so hopefully it won’t happen again.

[jamescarruthers]

This sounds useful mate.

Can you provide pictures and a how-to guide?

[eye of ra]

The oil trap which you can only just see in the picture should catch and return the oil back to the crankcase. When it becomes full of gunk the oil comes up the pipe and into the air pipe which then makes its way up to the throttle body and rots the gasket letting in air.

Remove pipes from throttle body (not all marked), connectors to air sensor, idle switch and ICV (DO NOT mix these up as connecting them the wrong way round will mean a new ECU) and cables (if you have a manual you will only have one). If you have no oil in the air pipe your idle problem may be elsewhere.

There are four bolts holding the throttle body, once these are loose the body will fall off as the gasket will be soaked in oil.

While everything is removed you will be able to get at the oil trap (metal can stuck into top of the crankcase, may still have foam raped around it, mine didn’t) the plastic cap with the pipes pulls off. There is now room to hit the trap with a rubber hammer repeatedly from side to side till it moves relatively easily, it’s quite strong. I then used some mole grips to wiggle it upwards till it finally came out, took some time. Be carefull not to distort the metel exit pipe or the plastic cap won't go back on.

Clean oil trap and throttle body and I used gasket paper to make a new one ( you may be able to get hold of a genuine one) then refit everything and top up water/antifreeze, if you clamp off water pipes before removing them you won’t need to do this.

Picture relates to a B18ED 104 other models will vary and if you break anything following this don’t blame me.

Not the best how-to but hope it helps.

[jamescarruthers]

That's brilliant mate, thank you. I'll have a go when I'm next off work as I'm baffled by my old 480's behaviour these days.

I'm sure ages ago someone had the part number of the "oil trap". Is these another name for it? Or is it just a case of cleaning it with carb cleaner and putting it back on.

[eye of ra]

Oil Separator 3342132 but as with most parts these days I couldn’t find a new one.

I think it’s just a metal maze inside the can, I could be wrong though so do at your own risk but I used washing up liquid and lots of hot running water to wash most of the gunk out (I also have a spare if it turns out to be wrong) then used brake and clutch cleaner till it ran clear, dried on a radiator then more brake and clutch and carb cleaner for good measure and dried again before refitting.

I used carburettor cleaner to clean the throttle body.

[Flying Dutchman]

Is this gasket replacement fix also applyable on the turbo engine?

[eye of ra]

Having looked at pictures of the turbo engine I’m not sure as I can’t see where the pipes from the oil separator go and Vadis shows an O-Ring rather than a gasket on the throttle valve.

A picture of the 2.0 on the other hand shows the pipe going to the throttle valve and Vadis shows a gasket.

[Flying Dutchman]

Hmm.. Just have to wait and see how it went for Swanny then.

[eye of ra]

UPDATE

Looks like the gasket was not the problem after all. It was leaking, proved by the smoke test I did, but it was not causing my idle problem.

Fault returned so I assumed leak had returned but on investigation that was not the case. On further investigation it turned out to be the TPS. At cold and low temperatures it tested and was working as it should however at higher temperatures the contact was breaking down and the ECU no longer knew the throttle valve was closed.

I think disturbing the TPS while fixing air leak must have temporarily fixed it.