Noddy OBD2 question; and low idle speed.

I've got a 2009 petrol Jimny. Didnt drive it for 2 weeks and since it has been occassional idling very low, about 500-550rpm. Doesn't stall, but feels like it might.

I've read a thread on hear advising cleaning the throttle body and idle valve, and possibly replacing the pcv. Will investigate those.

If I got a cheapy OBD2 tool would is it likely to point at any of these issues? Do these only show codes when the engine light is on?

As an aside Mrs Sheepish reported tonight that it took a lot of goes to start it after a brief stop on her way home. I tried; it started after I used the immobiliser key, which seems odd because it eventually started for her without doing that. And I never use the remote locking which I think is what precipitates the need for that.

Thanks for any advice

Hi Sheepish. Difficult one this as it could be everything from a split vacuum hose to a lamda sensor. I would recommend checking for any fault codes first.

Just to explain how difficult things can be to diagnose, my son (who's in the RAF) did a quick tour of duty. He left his car in the base car park for 4 weeks and when he came back it wouldn't run above a 1000rpm. After many hours and many phone calls to me, I advised him to call the AA. (Difficult to get the AA onto base at that time).

It tuned out that a fekkin mouse had nested above the sump guard and eaten through a lot of the wires!!

A temporary repair got him home and it took me 3 hours to solder and shrink sleeve a permanent fix.

A code reader may pick up a pending fault, a scan tool that shows live data would give you a better idea of what may be wrong. Does the MIL come on at key on? a fault that causes a low idle ought to show up something, unfortunately the most useful parameters for diagnosing idle problems are only available via the 'OBD1' datastream.

Yes MIL comes on with the key. Should have an OBD2 reader tomorrow so will see what it says. Took a lot of cranking to start it this morning I'm told, although started fine when I tried it, although it was warm by then.

Got a wireless OBD2 reader and a free app for my phone. Shows P0401 as a Last Trouble Code, which I think means the ECU has detected this once, but only once? A bit of Googling suggests cleaning the EGR valve. Looks a bit fiddly to get at but I think that's the next course of action. Of course today I started it and idling is fine. I want to spray a bit of carb cleaner around the vacuum hoses to test for leaks first.

What do your fuel trims look like? if you have a vacuum leak then it will show up as a lean mixture at idle. P0401 suggests a blocked passage between the EGR valve and the exhaust manifold.

Just for completeness, I had the EGR valve, and the pipe that connects to the inlet manifold off this morning. Soaked in carb cleaner. The little plunger in the valve was stiff and not returning when pulled down. A bit of a scrub and it seemed much better. Fitted everything again; must be a knack to getting the pipe and its gaskets back on I don't have. Anyway seems much better now. Have reset the MIL and the code hasn't reappeared. Thanks all for the advice.

Not so good. Ran fine after first clean for about 20 miles. Then same old rough idle. Had the EGR valve off again and soaked it in carb cleaner for 24 hours. It didn't seem to have a stiff plunger this time though. Seemed OK for a few miles but now back again.

Getting P401 again, which I know suggests a block between the valve and the inlet manifold. But to me this doesn't make sense for the rough idle. If I understand correctly at idle I shouldn't be trying to suck exhaust gasses into the combustion chamber? So I shouldn't be sucking to worry that the route between EGR and inlet is blocked?

Before getting into cleaning pipes and possible removing the inlet manifold (if that is necessary?) is there any way I can rule the EGR valve out of the equation? The valve isn't operated by a separate vacuum hose so I assume it doesn't have a diaphragm to leak?

Ta

The ECU may have dropped into a fail safe mode because of the fault code. What do your fuel trims look like?

Thanks. I have cleared the fault codes each time I've cleaned the EGR. I can see how to capture fuel trims on my ECU reader. Should I record them over a period of time? Under certain driving conditions?

Record them at idle and then at a medium load at 50mph or so in top gear.

Hi

Idle (and warm). Short term % between -2.3 and +1.6
Long term % between -10.2 and -7.0

Approx 50mph in 5th. 2600-2825rpm
Short term % between -3.9 and +4.7
Long term % between -9.4 and -7.0