Intermittent Idle and hesitation - Idea?

Hi

My poor 55 plate VVT Jimny is intermittently sick. Just driving a long the car suddenly looses all power and if you're going up hill struggles to maintain speed. Initially it was a momentary glitch, but since its service in October it has slowly been getting worse and now lasts for almost a minute at a time. If you stop and let the engine idle then it is a rough as... (some where around 300 rpm) with no fault lights. If you turn the engine off in the middle of this it restarts immediately without the problem.

Google is normally my friend in this type of situation and that seemed to point toward the crank sensor, which has been duly changed, but to no avail. I've had a go at monitoring the sensors and found that when the fault occurs it appears to not be updating the sensors (i.e. you get the same reading for all of them for the duration) but I wonder if that is because the ecu is struggling to correct for something else and therefore not communicating properly.

Anyway, any ideas greatly received... I've been told there may be a cam sensor which can cause this, but I can't even find a cam sensor to try changing

Hi. Just had this with our 2006 vvt. Replaced plugs and leads and both coils and all sorted. Error codes logged confirmed failed coil pack but safer changing everything as it was all original parts from factory

I would check that the plugs are properly gapped, you ought to get a fault light though, if only the generic misfire code.

Thanks for the responses. Going to start with a new set of plugs tomorrow. I would go for a coil pack too but I just seen the price!! ~£250 from halfrauds... so that will have to wait for a bit. I'm also going to have another go at finding the cam sensor, I've already bought one.. but it wasn't obvious where it fits but i'll have another look now I have a description of where to look. (i'm probably just being a bit dense!)

I've been monitoring the OBD port with the torque app and don't get any fault codes coming up, i'm finding it really strange given just how upset the engine goes

Williams wrote: I've been monitoring the OBD port with the torque app and don't get any fault codes coming up, i'm finding it really strange given just how upset the engine goes

OBD2 is very limited, its mainly for monitoring emissions systems, the main dealer tool uses a proprietary protocol. Try plotting RPM, it usually goes haywire if its a crank sensor problem, if its a coil or spark issue then RPM should slow as the engine cuts. One bad coil should throw a misfire code so I'm a bit dubious. Check the fuses and the battery terminals in case you have a bad connection, a power drop out might explain why the sensors aren't updating, can you monitor the data rate?

Didn't get a chance to check a lot of things today, but got some new plugs as I've no idea when they were last changed. But just to show that I really can be dense... I still can't find a cam sensor..



the only thing in the area i'm looking in, looks nothing like the spare sensor (and looks more like it is coolant related)



Thanks for the ideas Rhinoman a couple more things for me to check.

I'm not sure I quite understand how to monitor the data rate or even really which sensors to monitors. I've attached a log from the torque app where I was just playing with the functions as this is all new to me. This is the log which seems to show periods of time with no change to monitored sensors (almost as if the ecu has crashed and is just continuing to output the previous value)





I've not really done a lot with engines since rebuilding a couple of 4 pot 80s Vauxhall engines for a couple of old cavaliers, things have changed rather a lot since then..

Williams wrote: This is the log which seems to show periods of time with no change to monitored sensors (almost as if the ecu has crashed and is just continuing to output the previous value)

At what point (device time) is it misfiring?

Rhinoman wrote:

Williams wrote: This is the log which seems to show periods of time with no change to monitored sensors (almost as if the ecu has crashed and is just continuing to output the previous value)

At what point (device time) is it misfiring?

At 16:40 at idle and again at 17:08 (lines 1328 and 3029 in excel)

Goes on for about 50s the first time and 3m 20s the second time.

Well had a good day yesterday..

Replaced the plugs, but nothing was looking too unusual there. The ends of the HV connectors from the coil packs were a little discoloured and starting to show some signs of perishing.

Also managed to find the cam sensor tucked away at the back of the engine, which I also replaced. Only difficulty here was that the cable connector had been taped back on itself which makes me wonder if this has been an issue in the past.

Anyway, to cut a long story short - ran the car for about 15 miles with no problem evident. Whilst it is a little too early to be perhaps to be 100% confident I've fixed it, but I recon i'm about 80% certain. Mostly based on the difference to the car on acceleration beyond 3000 rpm. I hadn't realised just how poor it must have got, but it was revving happily and pulling nicely up hills. So i'm guessing the cam sensor had been on it's way out for quite a while..

Still many thanks to Rhinoman and Kirkynut for their helpful comments as i'd have never really got this far without their help - cheers guys