This is doing my nut. Peugeot 406 idle

[Larkspeed]

1998 Peugeot 406 Estate 1.8 16v 110hp

Description of problem as best i can:

When we start the car the revs can spike all the way up to 3000 rpm and stay there.

Usually once we start driving the revs will drop back to around 1000 rpm however they do this with a delay, meaning if you pull away and let the car rev to around 3000 and then clutch to shift the revs will hover for about a second, then they will drop to around 2000, then drop to 1500 and finally drop to 900 - 1000, this stepped drop takes about 4 or 5 seconds. (it's this stepping that made me first think of the idle control valve)

Sometimes on start they will drop back down and sit around 1000 rpm before driving but as soon as we start driving it acts as described above.

If we have to do a lot of off on driving, as in going to half a dozen different places with only short stops in between the revs can then go really silly.

If they do this then they will climb to around 3500 rpm and then start to bounce between 2500 and 3500, the only way to stop this once it reaches this point is to pull over and to the 10 second on, 10 second off reset on the system.

After the reset it will go back to acting like described in paragraph 2

There is no stuttering hesitation or loss of power while actually driving the car, the problem only seems to effect idle.

I have replaced both the Idle Control Valve and the Throttle Position Sensor and it has made no difference.

Diagnostics is out because it is pre 2001 so uses Peugeot own propitiatory diagnostic unit and the dealer wants way too much to do a code read on it. (dealers service centers here are stupidly expensive and very unhelpful)

[filbert]

Could be hit and miss, but I'd go for the coolant temp sensor.

[abaxas]

Is it fly by wire or actual cable driven for the throttle body?

If the car is revving without the throttle body moving. You have a air leak somewhere.

[Larkspeed]

As near as i can tell there is only one coolant temp sensor in this engine and it runs the guage, which works fine.

standard cable driven throttle body.

And there is no air leak i have already checked.

Plus if it were an air leak the problem would constant, as in it would always do it and always in the same way, not intermittent and doing it in various different ways

[filbert]

Has to have a coolant temp sensor, and not the gauge one.

[abaxas]

So where is all the 'air' needed to rev to 3k coming from?

Something is allowing more air in and the car is adjusting fueling to be stoichiometric.

[Larkspeed]

or there is a bad sensor and the ecu is causing more fuel to go into the engine which in turn causes more air to be drawn in in the normal manner causing the revs to rise.

Saying that just because revs are rising on their own has to be an air leak is flawed logic

[abaxas]

So where is this air coming from?

Through the throttle body and idle vavle dodar?

[Larkspeed]

yes correct through the throttle body.

if a bad sensor is confusing the ecu it could very well be instructing the icv to open up the butterfly and let more air in.

This is not a leak this is a result of bad information

So I will say again there is no air leak in the engine

[technodean]

Could be a number of things, Mine did this the other day which was the air flow meter, but it could be numerous things such as idle control valve (remove and spray with carb spray), air flow meter, Lambda sensor, crank sensor etc. If your due for an mot and it fails on emissions then its likely to be a maf or Lambda sensor as they are the 2 components which dictate your fuel mixture.

[Larkspeed]

Idle control valve and throttle position sensor have both been changed for brand new ones.

APK (mot) is not due until October.

IRC these engines don't use a MAF they actually use a MAP which does essentially the same job they just get the result a different way.

I'll see if I can't source a decently priced MAP, my main problem here is that parts in this country cost so much that blindly changing out parts to try and source the problem can quickly become more than the car is worth.

[peterb]

I'll see if I can't source a decently priced MAP, my main problem here is that parts in this country cost so much that blindly changing out parts to try and source the problem can quickly become more than the car is worth.

Might be better to bite the bullet and use the dealer diagnostics. Could be cheaper in the long run than just random component change.

Is it worth taking it to a Peugeot dealer in France?

[Larkspeed]

No I'm in the Northern Netherlands it's a long drive to get it into france.

Problem with taking it to the dealer is they charge like 200 euro just to scan it and then they will tell you they found problems and give you an estimate to fix it, they won't straight out tell you exactly whats wrong though. You will get a basic enough description of the problem to prevent them from scamming you and you will get a copy of the report when the repairs are complete so you know they did not replace anything that did not need it.

We live on a very tight budget which is why I have avoided the dealer.

To give you an example of dealer costs here, to get a key cut costs 100 Euro, this is without putting a transponder chip in it. They will charge you a further 85 euro for a transponder chip and then charge you 75 euro to program the chip to your car. Which means all in just a simple key costs 260 Euro.

I can get the same thing from the UK for under 70 quid.

[Rave]

Diagnostics is out because it is pre 2001 so uses Peugeot own propitiatory diagnostic unit and the dealer wants way too much to do a code read on it. (dealers service centers here are stupidly expensive and very unhelpful)

On my old peugeot it was possible to get a fault readout by making a simple jumper cable and then connecting two of the pins of the diagnotic socket. Then you'd sit in the driver's seat and watch while it flashed the engine management light on the dashboard. What ECU does it have?

[Larkspeed]

it has the Siemens ecu

however the jumper trick only works if there is a fault code stored in the ECU in which case the light would be on.

The light is not on so there will be no fault code.

What I would need to actual diagnostics to be able to see what each of the sensors are returning in real time, that way I could establish which sensor was at fault. I can buy the diagnostic unit but they are very expensive.

[peterb]

A quick google came up with this

http://www.peugeotcentral.co.uk/ftopic-8090.html

and another one came up with this

http://www.amazon.co.uk/gp/product/B0051CFGBA/

I have no idea about compatibility with your ECU, I am sure it uses one of the many standard protocols. Might be worth doing some further research. (I guess the device works with any Bluetooth device, doesn't have to be android based.