OK, have a weird problem with my Calibra Turbo (with 83k on the clock). For the last few months now, once on a warm engine, my tickover regularly settles at 1400 - 1500 rpm, for a while before dropping back to about 900.
Now I first assumed it to be the ISCV, however after cleaning the original and then swapping it for a known working one I have noticed no difference whatsoever. Stranger still, although it doesn't do it when it is on a cold engine, it doesn't always do on a hot one either.
Now the weird bit, having the fuel computer read out on instant consumption, I have noticed that the deceleration fuel cut off doesn't always work (ie. you don't always get 999.9 mpg). Now I know that as you approach the idle speed you won't see this anyway. Problem is if I back off at any revs, the instant read out reads anywhere between 100 to 400 mpg. Sometimes, it does cut off and I get 999.9, only for fuel to be used again a second or two later, sometimes to go back to 999.9 again. This ties in with what the car feels to drive, when you see 999.9 it decelerates as it should, but other times it feels like you've still got your foot on the throttle a bit.
Like I said it doesn't do this all of the time, but it is pretty frequent, probably 50% of the time. I suspected the throttle linkage sticking or the throttle cable, but after having a look at it, it doesn't seem to be, when moved by hand it certainly seems to return to its stop fast enough, even so, I gave it a liberal dose of WD40 - to no effect. I've also had the top hat off and checked the position of the butterfly, but it looks ok to me.
Other thoughts are TPS ? CTS maybe ? (although it was replaced last year).
Other than that the car runs absolutely spot on, no smoke, holds 9.5 psi boost, starts and runs fine. When I took the ISCV out there was very little contamination on it and it uses very little oil, so the engine seems to be in good nick, it's just got this damned annoying habit of revs holding up, and I'm pretty certain it's not the ISCV.
Any ideas anyone ?
Oh, and forgot to say, there are no stored codes either, it's just giving me code 12 over and over.
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Hi,
First thing to check is that the throttle cable isn't too tight. People have been known to 'adjust' them. It should have quite a bit of slack - but then, check that you can still get full throttle from the pedal :-)
If that's ok, then go on to check the throttle base adjustment is ok, and the throttles are nice and clean. If you need info on throttle adjustment, I can let you know, but this post is already too long! :-)
If that is all ok, then check the throttle position sensor (is it a switch or potentiometer on this model? If a potentiometer, check the output voltage varies smoothly with throttle opening. If it is smooth, try adjusting it slightly on its scres to get overrun fuel cut off to work. If a switch, make sure the idle contacts are being made.
A quick check that the idle position is being made is to squeeze the idle bypass hose at tick over - the engine speed should drop. Hold it like this for a minute or so (allows the idle integrator to saturate), then release. The engine should begin to rev - then over run cut off, then rev etc until it dies down.
Hope that helps,
number_cruncher
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Doubt it's the cable as he says it does drop to 900 . In my experience a thorough cleaning of the throttle housing / butterfly will benefit it immensely . Check that all the engine breather pipes are clear inc. the small ones and clear into the intake itself. And give the idling valve a clean .
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Well, thanks guys, finally got to sorting this out (been moving house). The problem was the CTS. Fitted a new one of those a week ago, and problem sorted.
Thanks again
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