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[SOLVED - FITV] 3rd Gen - Revving at idle?

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Engine/Gearbox questions and discussion
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 Postby dwallis92 »Thu Oct 12, 2017 2:38 pm

Hi guys, how you all doing?

So I apologise if this seems like a n00b question, I'm pretty sure it's normally something to do with vacuum lines but I've replaced most of them (run out of hose, need to buy more) and it's still doing the same thing. Basically, when cold it idles ~1200/1500 rpm, which is normal due to automatic choke and whatnot. It idles smoothly, doesn't sound rough and holds a consistent speed. Normally I let it idle for a minute or 2 before driving, but I don't let it get up to temp before pulling off. Instead I opt for little smooth, gentle acceleration and low engine speeds until shes up to temp, and even then I don't ALWAYS put my foot down :lol:

She runs and drives fine, nice and smooth as expected, but if I come to a stop before the engine is up to peak temperature it starts revving up a little by itself. It only revs from normal idle (~750/1000rpm), to about 1500/2000rpm and back to normal idle again but continuously, and only stops if I put the engine under load (like putting it in gear and lifting the clutch a little with the handbrake on). This settles the idle down to normal and if I then slowly depress the clutch, take it out of gear, and release the clutch again the engine idles normally, unless I tap the throttle in which case is starts revving again.

Keep in mind it's a 26 year old car which is mostly factory parts (including original clutch and alternator), so I do expect that some things are wearing out and are in need of replacing. I'm doing what I can when I can, but the rarity of these cars makes new parts hard to come by and expensive, and I'm strongly against "in-house refurbs" because, let's face it, these idiots don't know our cars (one actually told me on the phone that they "don't replace regulators because they don't normally go on these cars").

What I'm wondering is, aside from vac lines, what could this be? I have noticed that the radiator has been swapped for one off an auto and has the built-in oil cooler (so likely not the correct capacity for the car) and that my alternator is kinda naff, could either of these be the problem? My logic on the radiator is that if the engine is heating up faster than it's supposed to maybe it's misfuelling or something? And in theory if the clutch in the alternator is gone maybe there isn't enough resistance on the engine which explains why lifting clutch to the biting settles it down.

Btw what I mean by my alternator is "kinda naff" is that the tensioner kept snapping on the old owner, and ever since I fixed it I get flashing battery light at random points in the rev range (sometimes it just flashes continuously) and recently it's stopped correctly charging the battery if I go over 2000rpm. Really weird, I know, and I'm looking for a replacement. Also might be worth noting that I did recently discover that my main relay was suffering the common cold-solder joint issue and have repaired that.

If it's not cooling system, alternator, or one of the vac lines that I'm yet to replace then I really don't know what else it could be.

Car is a 1991 3rd Gen Prelude with B20A7 and manual gearbox (pretty rare as far as I understand it). Any help/advice is greatly appreciated. Really want to fix these little niggles and get back on with the bodywork as she desperately needs a respray so I can start showing her off :D
Last edited by dwallis92 on Tue Oct 17, 2017 9:25 am, edited 1 time in total.

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 Postby NafemanNathan »Thu Oct 12, 2017 8:59 pm

I should have read this thread first ;)

I had a very similar issue with my 3rd gen (Manual B20a7). It took a while to find it, but it turned out the FITV (Fast Idle Thermal Valve) was leaking air (wasn't sealing). You can remove the cap (whilst the engine is running) as adjust it.

Mine wouldnt adjust another, so I took it all apart and packed it out. Worked perfectly afterwards :)

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 Postby NafemanNathan »Thu Oct 12, 2017 9:11 pm

To determine if it's the FITV, remove the inlet pipe whilst it's surging and block the lower hole in the throttle body with your preferred digit. If the surging stops then your FITV isn't sealing properly.

Here's a link to my fix bud...

http://www.ludegeneration.co.uk/post105040.html#p105040

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 Postby dwallis92 »Thu Oct 12, 2017 9:16 pm

NafemanNathan wrote:To determine if it's the FITV, remove the inlet pipe whilst it's surging and block the lower hole in the throttle body with your preferred digit. If the surging stops then your FITV isn't sealing properly.

Here's a link to my fix bud...

http://www.ludegeneration.co.uk/post105040.html#p105040


That makes a lot of sense I'm definitely going to have a look at mine tomorrow, it's just really throwing me off that it settles when I put it under load.

Never actually met anyone with another manual 3rd gen let alone the A7 one ;) Is it just me or do the gear ratios seems a little close to you? I always get the feeling theres too much of an overlap, like changing gear isn't dropped the engine speed enough lol

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 Postby dwallis92 »Thu Oct 12, 2017 9:26 pm

NafemanNathan wrote:Here's a link to my fix bud...

http://www.ludegeneration.co.uk/post105040.html#p105040


I don't even think I need to check it after reading that lol I'm about 99% certain you're right. Going to have a little play with it outside my mates gym tomorrow. Thanks for your help mate really appreciate it :) Like you I shall soon be able to pull up alongside the bacon without them looking at me like i'm smoking a crack pipe behind the wheel lmao.

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 Postby NafemanNathan »Thu Oct 12, 2017 9:26 pm

It's perfectly normal to smooth out when put under load, as long as your Idle Air Control Valve is working properly.

Oh, and just don't keep reading my thread then... It gets a bit nasty :?

All later gen Preludes have pretty close gear ratios. Think we'd all benefit from a 6th or 7th gear really :lol:

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 Postby NafemanNathan »Thu Oct 12, 2017 9:27 pm

dwallis92 wrote:
NafemanNathan wrote:Here's a link to my fix bud...

http://www.ludegeneration.co.uk/post105040.html#p105040


I don't even think I need to check it after reading that lol I'm about 99% certain you're right. Going to have a little play with it outside my mates gym tomorrow. Thanks for your help mate really appreciate it :) Like you I shall soon be able to pull up alongside the bacon without them looking at me like i'm smoking a crack pipe behind the wheel lmao.

:lol:

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 Postby dwallis92 »Thu Oct 12, 2017 9:40 pm

NafemanNathan wrote:It's perfectly normal to smooth out when put under load, as long as your Idle Air Control Valve is working properly.

Oh, and just don't keep reading my thread then... It gets a bit nasty :?

All later gen Preludes have pretty close gear ratios. Think we'd all benefit from a 6th or 7th gear really :lol:


I think all cars could do with a 6th just to drop a few revs at 70 :lol: thats not Lude-specific :P

I think it is just me but I feel like final drive could be a lot shorter. Like I used to "play around" a bit on motorway with my mate and his tdi Golf (until he got bigger injectors and a remap) and he just couldn't keep up. We was barrelling along at 120 once, I floored and (his words) I left him like he was stood still. They seem to have far too much power up high to be dropping off at 130ish you know?

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 Postby NafemanNathan »Thu Oct 12, 2017 9:50 pm

120kmph right? ;)

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 Postby dwallis92 »Thu Oct 12, 2017 9:57 pm

NafemanNathan wrote:120kmph right? ;)


Mph..? Hey speeding is nonsensical. Einstein said that time is relative, speed = Distance over Time, the true distance we travel on a spinning planet orbiting a sun, orbiting a black hole that it's being pushed away from, all at indeterminable speeds. How fast was I going? I don't really know but I know it somewhere close to about 40% of the speed of light :roll:

Weirdly enough though my drivers license is squeaky clean :lol:


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