ABS Causes Idle to Wander??

[bmh.01]

Leading on from:
[SIZE=-1]http://www.cliosport.net/forum/showthread.php?t=293279
and http://www.cliosport.net/forum/showthread.php?t=281285

I've now discovered what is causing the idle revs to wander. If you jack the car up so a wheel is off the ground, start the engine the car will idle normally. Spin the wheel and the revs will rise until the wheels stops spinning where they will quickly fall back to normal idle.

If you disconnect the ABS sensors then this doesn't happen, pull the ABS/ESP fuses and it still does and is worse. It doesn't matter which wheel you spin it'll still do it regardless.

Doesn't look promising tbh, but at least i've narrowed it down I guess :dapprove:.

Very long shot but any ideas? Haven't really got any docs/manuals for the abs/esp system.
[/SIZE]

 

[Fred@BTM]

your car has esp?

 

[MarkM]

Copied this from an Audi forum

"The ECU raises the idle speed to 1100-1200 rpm when the idle switch is active but the car is rolling, in order to provide adequate vacuum for the brake booster."

So it looks like the ECU may be adjusting the idle under the conditions you describe but obviously in your case by too much

 

[GordonD]

In the computer field there are "bugs" and there are "features". A bug is where something is wrong and it causes a problem. A uses notices it, you fix it. A feature is where the situation the problem occurs in is so obscure that who the hell cares. A user notices it you say "sorry, that's a feature of that product, it probably does it for some good reason we don't know about, and if there isn't a reason what does it matter".

I'm trying to figure out why its a problem that your engine idle speeds up if you jack the car up off the ground and spin one of the wheels. It sounds like a "feature" to me.

 

[MarkM]

How does the idle control work?

Is it -

ECU opens the TB and increases fuel by a set amount for a given condition

or

ECU opens the TB and increases fuel until it gets the correct RPM feedback (closed loop)

 

[bmh.01]

In the computer field there are "bugs" and there are "features". A bug is where something is wrong and it causes a problem. A uses notices it, you fix it. A feature is where the situation the problem occurs in is so obscure that who the hell cares. A user notices it you say "sorry, that's a feature of that product, it probably does it for some good reason we don't know about, and if there isn't a reason what does it matter".

I'm trying to figure out why its a problem that your engine idle speeds up if you jack the car up off the ground and spin one of the wheels. It sounds like a "feature" to me.

Its a problem because it never did it before and it causes the revs to drop off very slowly when you change gear.

Copied this from an Audi forum

"The ECU raises the idle speed to 1100-1200 rpm when the idle switch is active but the car is rolling, in order to provide adequate vacuum for the brake booster."

So it looks like the ECU may be adjusting the idle under the conditions you describe but obviously in your case by too much

How does the idle control work?

Is it -

ECU opens the TB and increases fuel by a set amount for a given condition

or

ECU opens the TB and increases fuel until it gets the correct RPM feedback (closed loop)

Closed loop i'd guess but then again pass. It doesn't go to 1100-1200rpm though really, is does sometimes but it'll go as high as 2000rpm at times. And it never used to do anything like this.

 

[bmh.01]

your car has esp?

Yep and cruise/speed limiter too, the last of the 172s had them both fitted as standard. Esp became standard late 52 reg iirc.

 

[bmh.01]

Also if I pull the fuses out for the ESP/ABS it seems to go to 2k and hover around there and generally be worse. But disconnecting the ABS sensors removes the problem, which I don't get surely it should go about when the system is powered down too?

 

[ben_p]

hmmm,

 

[ben_p]

is the brake servo vacume hose tight? (back right of the inlet plenham, with the steel clip)

mine was just* loose, i used a jubilee clip as a temp test. and it fixed the problem

 

[bmh.01]

Very hmm indeed, did wonder if it might be interferance through a bad earth but dunno really. As it still does it when theres no power in the ABS/ESP computer I was thinking along the lines of as the sensors are hall effect devices they'll still generate the (albeit small) voltage pulse as the ABS ring teeth pass it. Hence why it goes away when they're disconnected.

 

[bmh.01]

is the brake servo vacume hose tight? (back right of the inlet plenham, with the steel clip)

mine was just* loose, i used a jubilee clip as a temp test. and it fixed the problem

Don't think its that as i've disconnected it and plugged the hole to test before and no difference. Will give it a try though got plenty of jubilee clips about.

 

[MarkM]

Its a problem because it never did it before and it causes the revs to drop off very slowly when you change gear.

Copied this from an Audi forum

"The ECU raises the idle speed to 1100-1200 rpm when the idle switch is active but the car is rolling, in order to provide adequate vacuum for the brake booster."

So it looks like the ECU may be adjusting the idle under the conditions you describe but obviously in your case by too much

How does the idle control work?

Is it -

ECU opens the TB and increases fuel by a set amount for a given condition

or

ECU opens the TB and increases fuel until it gets the correct RPM feedback (closed loop)

Closed loop i'd guess but then again pass I doesn't go to 1100-1200rpm though really, is does sometimes but it'll go as high as 2000rpm at times. And it never used to do anything like this.

I doubt you would have noticed it before if it was just a couple of hundred RPM. You have an idle control fault, obviously, but your ABS idea I dont think is the issue.

Well its not the TB so its either the output to control its position (ECU) or the rpm feedback.

 

[MarkM]

Also if I pull the fuses out for the ESP/ABS it seems to go to 2k and hover around there and generally be worse. But disconnecting the ABS sensors removes the problem, which I don't get surely it should go about when the system is powered down too?

If the ABS sensors disconnected and move the wheel they obviously cant see the wheel moving so it appears stationary and doesnt try to raise rpm.

On open circuit the ECU may default to seeing the wheels as moving for safety reasons. The ECU is driving the ouput not the power on the feedback signal.

 

[bmh.01]

Its just gotten a lot worse, any movement of the wheel now triggers the electric fault warning light and put its into limp mode so its nothing to do with raising the rpm for the brake servo you could put it in reverse or take the handbrake off now and the revs will wander but only before it goes into limp mode so just after you've started the car.

Once its in safe mode it drive fine though barring the 3k rev limit! Throttle action is exactly as it was before, so whatever its ignoring is the problem somewhere. The ESP/ABS still works fine so I don't think its that. Me and Has spend about 4 hours on it yesterday and found nothing at all which is very frustrating.

Got it going on clip Monday morning so that should provide some answers (i hope/pray!) just wondered if anyone had any other ideas to try in the meantime?

 

[Wiking]

No, But I cross my finger for you to find the gramlin.

 

[bmh.01]

Gone into a bit of depth here but just incase it happens to someone else.

Fixed it, couldn't just sit there and leave it as it was eating away at me . Now the revs would rise with rotation of any wheel, putting the car in reverse, or taking the handbrake off.

So I forgot about component failure as those are seperate systems to both the throttle and each other (barring the abs and handbrake switch) so started thinking along the lines of a wiring failure, started digging through the wiring diagrams looking for something common to them all and I found it in connector R107 which is the engine/dashboard connection that goes through the bulkhead. When I saw its location I had a pretty good idea that it might be the problem as its located behind the washer bottle which has an open grill so went straight along the lines of water).

Plug/socket is in the corner behind the washer bottle.

I removed the washer bottle and disconnected the connector and whilst the connector was dry the loom itself was f**king soaking inside the loom tape and what happens it the water gets into the loom which isn't a problem as long as they're aren't any cuts in the insulation but it migrates up the loom into the back of the plug and shorts pretty much everything out. Now you get very high resistances between the wires but its enough to cause problems with something as sensitive as the FBW throttle. When I first started I was getting resistances between 70-150kΩ, this would still cause problems. After throughly drying the loom and back of the plug, coating both in WD40 and rewrapping the loom with LOTS of tape to try and stop it happening again I got the resistances up to 850kΩ on the lowest one and 1.5MΩ+ on the others I tried it again any by god what a difference. Throttle responce is night and day from before.

Now while i'm not 100% happy with still getting slight tracking between the wires it works and you can run 1100v plant on a 1meg test so it'll have to do. The test should pick up as any other water drys off.

It ony effected the bottom pins on the plug as the top ones all tested 20MΩ+ but unfortunately the bottom is where the throttle pedal connections are.

 

[Wiking]

First, glad that you found the problem. Secondly, now I'm starting to think that may be my problem here is the same. For now, everything is usual (from the last post in my thread). In few weeks I'll do service for mine and will check this too. Hope to not have any problem in the mean while.
So, after all it was an electrical problem.:rasp:

Lior

 

[MarkM]

Nice work.

Wiring faults are the hardeast to find causing strange and intermittent problems.

Want to fix mine.

 

[bmh.01]

Nice work.

Wiring faults are the hardeast to find causing strange and intermittent problems.

Want to fix mine.

No! :rasp: Had enough of Clio wiring for a little bit funnily enough .

Got a feeling its a commonish problem, went to show Has yesterday and he says the throttle responce isn't anything like mine is now on his 55 182. Obviously not enough to cause problems but enough to loose responce.

 

[LegoHead]

I am thinking I may have a similar issue. The revs take a while to drop off and once in a while when i start the car the revs climb to 3000rpm and keep climbing....

I'll check brake vacuum line and then might pull off the scuttle panel.

 

[Wobba]

Resurrecting a thread here, apologies, but before I start taking my car to bits again has anyone else had this issue with the wiring behind the washer bottle getting wet and causing a poor idle?

 

[bmh.01]

I would imagine not a common problem as mine was self inflicted by accidentally bending the skuttle drain hose back on itself so the skuttle wouldn't drain.

 

[Wobba]

Ahhh ok, so it was deep in water. Mines only a bit damp from messing about with the washer pumps.

I'll look elsewhere first, thanks for the fast reply.