Idle Experts...

[v6Max 0]

I've got my 205 back on the road after 6 months of "work" on it and all is well apart from strange idling behaviour...

 

At start it idles high as expected, the SAD closes within a few minutes and "hot" idle is then around 900 - 950rpm; so far so good.

 

When I drive the car though and come up to junctions, traffic lights etc sometimes it will idle at 900 - 950rpm but other times it will decide to idle at 1200 - 1500rpm. There's no particular set of circumstances other than the fact that the car has been driven and I can't replicate the problem by leaving the car to idle in my garden for say 45 minutes. Also when it does idle it doesn't hunt it just sits at whatever speed it has decided it wants to idle at.

 

I've checked; the SAD, the TPS, for airleaks by placing a plate over the AFM inlet and the car stalled which I would say suggests that are no leaks, for dodgy connections by "waggling" the wires to the TPS and AFM.

 

When I put the car back together I cleaned everything in the inlet track, so hoses, AFM etc are clean. The vacuum hose from the TB to the dizzy is in place.

 

I don't know if the orientation of the AFM would affect anything like this; mine sits vertically rather than horizontally. The tamper proof cap over the mixture adjustment screw is still in place so the previous owner probably hasn't adjusted it.

 

Any body got any ideas...

 

Confused of Kent.

[welshpug 1,627]

check the tension of the throttle cable, shouldn't be tight as you'll still get Full throttle with a bit of slack, as well as that check how well the throttle closes the srings sometimes aren't positioned correctly making them jam occasionally and sometimes are just weak.

[v6Max 0]

check the tension of the throttle cable, shouldn't be tight as you'll still get Full throttle with a bit of slack, as well as that check how well the throttle closes the srings sometimes aren't positioned correctly making them jam occasionally and sometimes are just weak.

 

Should of said I've checked that as well. There's just a little slack when the throttle returns to the stop; definitely not sticking either as I got the bonnet open today when it started doing it after driving it to work and the throttle appeared to be closed.

[Anthony 1,000]

When it's idling high, give the throttle a sharp blip - does the idle speed then come down? If so, it possibly might be what's written above, or is more likely a worn throttle body and another one will fix it (had this on both 8v's and Mi's).

 

If it doesn't come down, try squeezing the pipe to the SAD to block its air supply - does it then come down? I've found on some 205's, after an extended spell on the motorway the SAD manages to cool down enough (I assume from the airflow under the bonnet) that it partly reopens and the idle speed increases.

[v6Max 0]

When it's idling high, give the throttle a sharp blip - does the idle speed then come down? If so, it possibly might be what's written above, or is more likely a worn throttle body and another one will fix it (had this on both 8v's and Mi's).

 

If it doesn't come down, try squeezing the pipe to the SAD to block its air supply - does it then come down? I've found on some 205's, after an extended spell on the motorway the SAD manages to cool down enough (I assume from the airflow under the bonnet) that it partly reopens and the idle speed increases.

 

It doesn't normally drop back down following a blip although it did this morning but the thing is the throttle definitely appeared to be closed when I looked i.e. before I "blipped" it. The other thing is the car has only done 77k miles and I'd be surprised if the TB was worn but it's definitely something I'll check.

 

I checked the SAD because I suspected the same thing i.e. it may be opening again but it was definitely closed.

 

Does this sound like a mechanical rather than electrical issue then? I'd toyed with the idea that the 205 was in effect applying some form of cold start enrichment on an intermittent basis but my temp guage is reading fine (although I don't know the electrical system well enough to know that the ECU uses the same temp sensor as the gauge).

[Tom Fenton 1,526]

My 1600 also does something similar, when warmed up up either idles at 900-ish RPM or 1100-ish RPM. The SAD is working properly and has been cleaned out and the idle doesn't fall when closing off the hose, I've checked for air leaks, the throttle body has been off and been re-bushed. The throttle is closing properly, and I've cleaned out all the passageways in the throttle body. The vacuum advance can on the distributor is new so there is not an air leak there.

 

All in all I can't seem to make it any better, so am putting it down 50 % to the little French gremlin that lives under the dash, and 50% to it being a 18 year old Peugeot, and leaving it at that.

[v6Max 0]

My 1600 also does something similar, when warmed up up either idles at 900-ish RPM or 1100-ish RPM. The SAD is working properly and has been cleaned out and the idle doesn't fall when closing off the hose, I've checked for air leaks, the throttle body has been off and been re-bushed. The throttle is closing properly, and I've cleaned out all the passageways in the throttle body. The vacuum advance can on the distributor is new so there is not an air leak there.

 

All in all I can't seem to make it any better, so am putting it down 50 % to the little French gremlin that lives under the dash, and 50% to it being a 18 year old Peugeot, and leaving it at that.

 

:-) Suspect that's what I'm going to end up doing although may try replacing the temp sender first and cracking open the AFM to check that out.

[Tom Fenton 1,526]

If the ECU temp sensor is u/s it will overfuel all the time and hence stink of fuel. The AFM is worth trying though, I have retracked mine and its still the same.....

 

However I don't want to mess with it anymore, and it will do between 36 and 40mpg on a good run, so that is good enough for me.

[mhyphenl 10 1 Cars]

:-) Suspect that's what I'm going to end up doing although may try replacing the temp sender first and cracking open the AFM to check that out.

 

Just a quick point, there may be an issue with the AFM not being in its standard orientation. If the flap is not returning to its more closed positions as easily because of the way its mounted will that not hold the revs up. It could explain some inconsistancy!

[Rob_the_Sparky 9]

Yeah, sounds more mechanical than electrical. On the electrical side though MAYBE it is the idle switch not quite engaging? Not sure that it would even have this effect and think either throttle plate or AFM more likely but thought I'd mention it just in case

[saveloy 8]

Sounds like a classic case of AFM spring wear. You could try tensioning the spring to see if that helps. If it does, then simply re-position the track arm down a tad, so as to bring down the fuelling back to a normal level. I've written a complete guide regarding this, let me know if you want it emailed over.

[v6Max 0]

Sounds like a classic case of AFM spring wear. You could try tensioning the spring to see if that helps. If it does, then simply re-position the track arm down a tad, so as to bring down the fuelling back to a normal level. I've written a complete guide regarding this, let me know if you want it emailed over.

 

The guide would be useful.

 

Looked at it again today and have changed things around so the AFM is more or less horizontal now.

 

Will be using the Haynes guide to check through a few things tomorrow and to get the idle set at best as possible. I've got a suspicion that the previous owner has played around with more things than I first thought.

[v6Max 0]

Looks like the problem may be the TPS, or more precisely the wiring to the TPS. When it was doing it's 1.5k idle today (having spent an hour on the drive idling at 950rpm) I found that waggling the TPS loom dropped the revs - looks like I'll be re-wiring the switch...