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Chasing a slightly lumpy idle...still

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Old Aug 21st, 2018, 13:36   #61
Laird Scooby
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Originally Posted by AllHailKingVolvo View Post
You could be right about it being as good as it gets. Something feels a bit amiss but there has to be a limit when it comes to “firing the parts cannon” at the car!

I’ll check the knock sensor and see how it all looks. The Bosch units are cheap enough so I may replace it just to be sure.

The charger is a Halfords unit which was about £15 as I recall...it’s the only one I could find that was long and slim enough to fit the deep cigarette lighter socket in 7/900s!
I've never had a problem getting any aftermarket charger to fit the cig lighter in any Volvos i've had! They're the standard diameter and depth so not sure what problem you had?

If you could get a video of the engine and upload to Youtube we can all have a listen and see if anyone picks up on anything. Meanwhile if checking the inlet manifold bolts don't have any effect and temporarily disconnecting the knock sensor doesn't either then it may be the knock sensor has died - it's unusual but it happens.

The other thing is you may have a slightly sticky piston ring that reduces compression on one pot at idle. Might be worth adding a litre or so of synthetic ATF to the engine oil to help clean the engine internally (also revives weak oil seals and works wonders on hydraulic tappets, shame the redblock doesn't have them in that respect!) and hopefully free that sticky piston ring.
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Old Aug 21st, 2018, 14:57   #62
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My memory of why the long slim charger was required is lost in the mists of time! I thought the socket was deeper than usual, but I’m probably remembering it wrong. I think when I had my 945 the positive pin in the hole was degraded from years of use (the fag lighter looked like it had been stored in the sea and used to light cannons, despite the car not smelling of cigs whatsoever...very odd!) and my tapered one didn’t sit home quite enough to make decent contact. I tried several others and didn’t have any joy, so sought out the long thin one from Halfords which has been fine but may well have an issue now as it’s a couple of years old.

I’ll get a vid recorded ASAP. Very good suggestion re the ATF, should I treat it as a flush and change the oil after a certain period, or just pop it in and drive it as per?
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Old Aug 21st, 2018, 15:00   #63
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I'm with LS on this one, a youube video would be very helpful in seeing exactly what's going on.
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Old Aug 21st, 2018, 15:28   #64
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I’ll get a vid recorded ASAP. Very good suggestion re the ATF, should I treat it as a flush and change the oil after a certain period, or just pop it in and drive it as per?
Just add about 0.5 - 1.0L to bring the level up to maximum it and drive.

Change the oil at your normal intervals, if you find it's cleaned a lot of dirt from the engine, i'd suggest adding a litre of ATF before topping up to the correct level with your normal oil when doing the change.

Depending how clean the next oil is when you change it, you may not need to continue adding ATF to the oil, if it's clean and idling smoother then you know that's the problem - or was by that time.

I used the same trick on my last 740 (B230E), my Jeep Cherokee and my current 760GLE, not to mention on both my Rover 827s (one of which i still have, the other was sold) frequently as the Honda V6 engine in it is prone to tappet rattle at times. The ATF prevents/cures that as well as keeping the engine clean and the seals in good condition. Also recommended it to many others, they've used it and all had favourable reports.

PS, worth trying another car charger for your phone!
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Old Aug 21st, 2018, 17:56   #65
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Intake manifold tightening - make sure this is done evenly and that the gasket is evenly compressed. Its easy to do it unevenly and when the gasket gets a few years old and brittle the uncompressed end can break out leaving a big hole.
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Old Aug 21st, 2018, 18:38   #66
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Thanks Dave and Tony!

Did a bit more sleuthing this afternoon, the intake manifold bolts are all drum tight and there is no air ingress via the gasket or injectors (tested with carb cleaner) all injector solenoids are happily clicking away and all seems content in that regard.

BUT...the throttle position switch doesn’t appear to be working. It’s not clicking, and the car runs identically whether it’s plugged in or unplugged. No note or running texture change when it’s unplugged with the engine running. Idles identically (slightly lumpy as per usual) and revs identically.

I’m now wondering if the TPS is shot, obviously. Would a failed TPS leave the IAC valve open at all times, causing the MAF to be confused and the engine to lean out excessively?
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Old Aug 21st, 2018, 21:41   #67
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Thanks Dave and Tony!

Did a bit more sleuthing this afternoon, the intake manifold bolts are all drum tight and there is no air ingress via the gasket or injectors (tested with carb cleaner) all injector solenoids are happily clicking away and all seems content in that regard.

BUT...the throttle position switch doesn’t appear to be working. It’s not clicking, and the car runs identically whether it’s plugged in or unplugged. No note or running texture change when it’s unplugged with the engine running. Idles identically (slightly lumpy as per usual) and revs identically.

I’m now wondering if the TPS is shot, obviously. Would a failed TPS leave the IAC valve open at all times, causing the MAF to be confused and the engine to lean out excessively?
Can you get the TPS to click by adjusting it Phil? If not then it sounds FUBAR and yes, it will cause idle problems. If it doesn't make when it's meant to be idling, the idle settings won't be used by the ECU and it won't keep the idle speed as it should with the IACV but will treat the engine as if it's being driven on a very light throttle.

You could prove the point by bridging out the two wires that go to the idle switch in the TPS, i'll look them up later but it would be fairly obvious when you get the right connections and the idle should change.
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Old Aug 21st, 2018, 23:23   #68
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Pop the link bar off and see if it clicks then. Sometimes when you take the throttle body off it doesn't go back in the same place and needs adjusted.

Throttle body does need removed and cleaned every few years with intake cleaner. Maybe its not closing properly.
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Old Aug 21st, 2018, 23:46   #69
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Pop the link bar off and see if it clicks then. Sometimes when you take the throttle body off it doesn't go back in the same place and needs adjusted.

Throttle body does need removed and cleaned every few years with intake cleaner. Maybe its not closing properly.
It may not click even with the link bar off Tony - that's what i had on mine because the throttle butterfly wasn't only dirty but had been adjusted by some half-wit trying to increase the idle speed on a car that is non-adjustable!

Once the butterfly is clean, as long as the TPS is capable of clicking it can be adjusted into the right place and it should bring all the idle properties into play when the throttle is released, including the IACV operation.

Might have to go right back to basics like i did, earth out that red/white wire near the expansion tank to disable the IACV, adjust the throttle stop screw to the base idle speed (600rpm without checking i think) with the air bypass screw fully in, unscrew the air bypass to give 700rpm, adjust the TPS so it clicks with the throttle closed, remove earth wire to allow IACV control again and hey presto - 900rpm steady as a rock!

While i still had the earth jumper in place, i checked/adjusted the CO to give 1% as per spec and it remained as it should be when the jumper was removed.

Worth bearing in mind mine is the V6 so the engine speeds and certain parts might be in different locations but that's basically the method - again, worth double-checking for the redbocks just in case.
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Old Aug 22nd, 2018, 16:06   #70
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Okay, I have made progress!!

The TPS wasn’t clicking or seemingly doing anything. On further inspection, the butterfly adjustment screw was wound right in (possibly by the same half-wit you mentioned, Dave!!), so the car was idling at the right speed (900ish rpm) but wasn’t using the IACV at all.

I’ve since reset everything, have adjusted the TPS so it clicks just after the butterfly moves, tweaked the length of the link arm so it all sits right and wound the butterfly stop screw out to the right spot for the butterfly to be shut at rest. I had to wind the butterfly spring round an extra half-turn as it was a little slack but it’s all fine now.

The car is instantly better. It feels more responsive and although I’ve only driven it for 20mins it seems like the hesitation under power has gone. The idle is still a tiny bit uneven but much better than it was. I may change the IACV just for the sake of covering all bases, as when it starts, revs initially fall to 400rpm or so then climb up to 7-800 where it sits happily at idle. I suspect that the IACV is a little tired, but I think I may have sorted the problem that has had me scratching my head (and everyone else’s here!!) for the last few weeks!

Ironically, I know the TPS was one of the first things you suggested, Dave...I could have sworn it was clicking back then! I may have just been hearing my small brain rattling around in my skull, though...
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