I’ve just had a fun few hours preparing the Capo for its MOT (annual inspection) and one of the issues I wanted to get around to sorting was the slightly high tick-over.
For quite a few months now the idle has been 1,500 – 1,550 when warm – not enough to be troublesome, but noticeable. Problem is ….. I’ve plain forgot to do anything about it once the ignition was turned off! So today I dusted off the cable and charged the old ASUS notebook and plugged in.
Thankfully it was just as I hoped, the TPS (Throttle Position Sensor) was not at zero with a closed throttle. It was reading 1%. A tap on the ‘TPS Reset’ had it reading 0% and the idle was fine once again. So, the question is, have I got a TPS on its way out, or was it simply the fact that I hadn’t done a reset in 18 months ( 20K+ miles), something I used to do at every service. I’m hoping it’s the latter and will endevour to make sure I hook up TuneECU during all future services. Funny really that a tool I used to hook up on an almost weekly basis slowly slid to the dark recesses of the workshop over time.
A couple of folks have asked what the symptoms where that prompted the replacement of the check valves (AP8104251). Well, for a while I’d had an intermittent ‘cough’ or momentary stumble when lifting the throttle off idle …. maybe once every twenty times or so. More than enough to make your heart skip a beat when you think she’s about to stall just as everyone’s powering away from the traffic lights! Other than this annoying habit, everything in the garden was Rosie. Or so it seemed.
I’d cleaned and rebalanced the throttle bodies and all the vacuum hoses and inlet rubbers were perfect as they’d been replaced – but it kept happening. In the end with nothing much else to go on, I’d pulled the check valves and found them both to have failed.
Since replacing them, I realise there were other symptoms – very subtle – and the sort of thing you adapt to without realising it.
- Reduced engine braking. This was really noticeable within a couple of miles after the valves were replaced – Engine braking is certainly stronger now
- ‘Burble’ from the exhausts on overrun. This is greatly reduced, especially at low RPM
- Eratic idle during warm-up. The idle became lumpy at 65°C then smoothed out again by 70°C – now stable throughout.
With a few hundred extra miles under the belt, it’s fair to say that the intermittent off-idle stumble has well and truly gone which is great of course …. but I do miss that bit of ‘Burble’ on the overrun! So if you have idle issues and any of these symptoms ring a bell, then take a moment to check the valves as well as the usual old favourites – IACV, vacuum lines and inlet rubbers. You might be surprised.