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 Posted: Mon Apr 16, 2012 10:18 am |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Hi Guys,
2000 so non multplexed 1.4 auto. Starts idles and runs normally for awhile then the idle speed will move around randomly between 800 and 1100, sometimes it will rise to about 2500 for just a brief time and when it does this it sounds 'hollow' as though its lean and hunting for fuel.
I'm a retired old plant fitter so trying to keep the diagnosis at a mechanical level for the moment which is what I understand. The way I look at it is that it has a cable throttle which is not being moved so either the idle controle gadget is faulty (or maybe the data to it) or air is intermittently being allowed into or getting into the inlet manifold. My first thought was the purge valve but if I block the pipe it makes no difference and even if left open the revs only rise a tad. I guess my next move is to check every other piped connection to the manifold. Not had the idle gadget off yet, maybe someone can tell me if its just a controlled air admission valve or if it actualy mechanicaly opens the throttle? After searching the forum I measured the resistance of the engine temparature sensor which was 2.5k, is this about right? Anyway I temporarily substituted a fixed 2.5k resistor which made no difference. I'm happy to plod on with it, just looking for any advice or comments that may make my life easier.
By the way plugs are bosch.
I appreciate that the problem may be electronic but I'm trying to work out whats happening mechanicaly before working back from there. (effect then cause if that makes sense)
Bill.
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Posted: Mon Apr 16, 2012 1:23 pm |
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Joined: Feb 10, 2010
Posts: 4266
Trade Rating: +4
Location: Palestine
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try to clean the throttle body with carb cleaner
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Posted: Mon Apr 16, 2012 5:32 pm |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Hi Timon2210,
I packed in when it got dark but still not making much sense of the thing. I have both an aerosol and can of carb cleaner so will be pulling the idle control gadget tomorrow and giving it a clean, not sure about the throttle body, its cable operated and snapped hard shut on idle so dont think its the problem but I'll give it a good clean anyway. Give me a good old fashioned carburettor anyday, lol.
Bill.
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Posted: Wed Apr 18, 2012 5:39 am |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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It's been raining the last few days so not been able make much progress. Temporarily blocking the brake vac connection made no difference. Found about an extra unexpected 2 volt drop on cranking (2v measured from battery -ve to engine block/bodywork so a battery neg wiring problem) I suppose in theory this might have been enough to periodicaly cause the ecu to loose a few brain cells from its 'learning memory' but thats probably a long shot. Anyway an extra strap from battery neg to bodywork fixed that and it now cranks like a good 'un.
Bill.
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Posted: Sun Apr 22, 2012 3:57 am |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Guys I really need help from someone who understands the electronic control system (the clever part) of the 206. I've eliminated the possibility of air getting into the inlet manifold either via the purge valve or anything else connected to the manifold. I've removed cleaned and inspected the idle control valve, my belief is that the icv is working ok but is the culprit in that it is wrongly being told by the ecu to 'open up' so increasing rpm. What I need to know is what sensor problems would persuade the ecu to do that? As I've said before I've already tried substituting a fixed resistor for the the engine temp sensor without any luck, I assume I could do the same with any of the analogue sensors for the purpose of elimination. I've cleaned the crap from the ecu connector, and the bosh plugs are now new bosh plugs.
Bill.
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Posted: Sun Apr 22, 2012 4:11 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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ICV might be actually faulty and needs replacing.
Could be an injector issue, or indeed the EGR canister line playing-up.
Definately worth trying a different ICV though.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sun Apr 22, 2012 7:43 am |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Hi v9977 and thanks for the reply, I'm getting resistance readings of just under 50 ohms for the icv so the stepper motor coils are ok, I've also cleaned and examined it thoroughly but can't identify any mechanical problem with it . I suppose it could be something obscure so I'll try to borrow a known good working icv and try it. Mine is 1.4i petrol so no egr valve, did you mean the purge valve? ( the gadget behind the expansion tank), if so I've checked it and its not that.
Bill.
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Posted: Sun Apr 22, 2012 12:32 pm |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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Hi Bill
It takes a lot of things to be running sweetly to achieve a low steady tickover on modern engines and it can seem a bit daunting but take things one at a time. Always best of course to check first for any stored fault codes if you have the means to be able to do that. Assuming you've done the usual boring stuff of making sure plugs and air cleaner are in good condition etc
The fact it starts well and runs fine for a while but then gets lost as the engine warms up then I would look first at your precat lambda sensor readout. The ECU will be looking to the lambda for feedback under steady rpm conditions like idle for fine trimming the fuel/air mixture so it is critical for obtaining a good idle.
Sounds hi tech i know but you have the equipment ( a multimeter) to easily check it out already. It's easy to find your pre cat lambda, it'll be the first sensor stuck in the exhaust and it will have 4 wires to it. Two will be the same white colour (those will be the lambda heater wires) and then you'll have a black wire which is the signal wire and a grey which is the sensor earth.
Ok now with the engine running and warmed up the signal wire should be producing a flip/ flop oscillating voltage of between 0.15v to 0.85v when compared to earth and switching around every second. To measure it then you'll need to back probe the connector ( ie slide a metal pin down in alongside the black wire until you get contact and a reading when connected to your multimeter)
So it should look much like the top trace in the pic. The figures will be jumping about quite fast on a multimeter but you'll be able to see it looking close to the above. What you don't want to see is a flatline, nothing happening signal or a very slow response
You can also check out the lambda sensor heater wires ( the two of the same colour), with engine running then there should be 12v between the two wires although this will switch off momentarily at regular intervals. This is needed to keep the sensor hot as it needs to be around 600C
With everything turned off and the lmabda connector disconnected you can check the heater for continuity by looking for a very low resistance of just a few ohms. Infinite resistance means no circuit there and no functioning heater
Try that first and see how you go
Mechanically then you'll have a stepper motor - an in/out small valve in your ICV to control idle accurately and this can become gunged up and cause erratic idle and poor pick up from low rpm. There's a "how to" clean your stepper motor on the forum
Your engine temp sensor will change resistance as the engine warms up, typically 10k at 10C falling to maybe 200ohms at 100C
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Posted: Sun Apr 22, 2012 3:26 pm |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Excellent post there.
Good of you to take the time to write it.
@Bill: The carbon-canister and purge valve is part of the EGR and is present on all 206 models I believe.
Normal R reading on a stepping-motor coil does not necessarily mean the part is working properly.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sun Apr 22, 2012 3:46 pm |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Hi Deckchair5,
Well you've certainly given me a few things to think about. I dont have any means of checking stored codes so I suppose I'm working on it a bit blind really but no option so Ill soldier on with it. I'll check the pre cat lambda in the morning, I understand completely what I am looking for thanks to your excellent description. I have a schlumberger scope I could use but if the oscillation is at about 1 sec then I guess the meter will be fine. My bigest problem is a lack of available information, I have the Haynes book which is useless and a cd I bought which is even worse. Most of the sensors seem to be analogue so should be easy to check with a meter but only if its known what to expect, same with things like the crank speed sensor, I could look at the waveform on the scope but unless its obviously corrupted I dont know what the shape or voltage of the waveform should be. I was a plant fitter all my working life so dont mind getting my hands dirty but this hi tech stuff is driving me bonkers, lol.
Bill.
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Posted: Sun Apr 22, 2012 4:03 pm |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Hi V9977,
Yes I have a purge valve but no egr, unless I've got it totaly wrong the egr is only on the diesel version, the purge valve just draws off the fumes from the unvented fuel tank whereas an egr system recirculates a portion of the exhaust gasses. When the fault first came up I would have bet my socks on it being the purge valve as it seemed an odds on favourite but I've checked it and its fine.
Its getting late now so I think Im going to forget all about 206's for tonight and go find myself a large brandy before bed.
Many thanks to Deckchair5 and yourself for your advice, its good of you to help and much appreciated.
Bill.
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Posted: Sun Apr 22, 2012 11:34 pm |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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You're right.
EGR only on diesels.
Purge canister is not considered EGR and thanks for setting me straight on that.
Let us know what the issue is when you find it. 
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Mon Apr 23, 2012 1:05 am |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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Hi Bill
You have a scope? Ha! You were leaving this info til last eh! Always handy if you're getting into deeper investigations
The crank/rpm sensor detects engine rpm of course but the engine won't be allowed to start unless it detects minimum rpm and I would guess your rpm gauge is working so you can forget about your rpm sensor for now and concentrate on the ones that really affect tickover
Classic lambda problem symptoms are excessive fuel consumption - often only 2/3rd mpg of what it should be doing, very uneven tickover and MOT exhaust emissions failure of course
On a 2000 car I would be pleasantly surprised if an original lambda was still functioning properly as they are sited in a very hostile environment for electronics
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Posted: Mon Apr 23, 2012 4:28 am |
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Joined: Apr 15, 2012
Posts: 23
Trade Rating: 0
Location: uk
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Raining here at the moment, can't easily get the car under cover so giving it a rest for today. Fuel consumption is about 35 round town so not far off what I would hope for and passed its MOT 3 months ago with no emission issues. Despite this I think you are right and the lambda sensor is a very likely candidate, its definately original and the car has notched up lots of miles. Tickover's been uneven for awhile but only in the last 3 weeks has it started to pick up to 2500 or even 3000 rpm (just occasionaly and only for a few seconds). If it were manual it would just be a nuisance but being an automatic it powers off like a rocket, the brakes will hold it but it's still dangerous.
I much appreciate your advice and input.
Bill.
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Posted: Mon Apr 23, 2012 5:06 am |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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Ah there's so much more useful information there in that it recently passed emissions and mpg is good but it powers off like a rocket. This sounds more like symptoms of MAP sensor problems (and less symptoms of lambda probs)
Your MAP (that's your manifold absolute pressure sensor) is a sensor very similar to the old vacuum pressure gauge and determines what pull of air the engine is making compared to outside atmospheric pressure, put simply, how much suction is the engine drawing? From that the ECU can guess how much fuel to put in to the injectors to get the right fuel/air mixture. The sensor also has an integral inlet air temp sensor (IAT) as manifold air temp also plays a small part in working out what mass of air is being drawn in
If the sensor readings are wrong then it can go either way, a weak mixture means it feels like it's being strangled and power take up will be poor. On the other side, if it's running too rich then it will feel like it wants to go all the time and as soon as you give it any air at all at the throttle it powers away strongly. Testing a MAP sensor can be done with a vacuum pump and multimeter but the quickest way is by comparing by substitution and they are not too pricy at around £30
You can use your multimeter again to look at your MAP. There will be 4 wires. a 5v ref voltage, earth, IAT and your MAP. Your MAP ranges from around 0.5v to 4.5v depending on throttle opening. With engine off it's measuring atmos press so will be near the maximum and therefore near the ref voltage of 5v. At tickover then the vacuum will be fairly high so voltage will be around 1.5v
The figures aren't so important as the ECU will adjust to suit but what I would be looking for from the MAP is consistent and repeatable readings and quick response to throttle movements, settling back to the same figure at tickover (if you can get a consistent tickover from your engine. Ha!)
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