Fast idle fault

[CitroJim]

Mike,

If you want to test the pot, it should read around 1.5K between the brown and black wires. This is the track resistance and will not change with throttle position.

Between the brown and blue wires, it'll read 2.2K closed throttle and 1.75K wide-open throttle. Between the blue and black wires it'll read 1.15K closed throttle and 1.65K wide-open throttle.

A surprisingly small swing really. The above figures are nominal and will vary slightly between pumps depending on the idle speed and full speed adjustments. The two pumps I have, the figures are very similar.

If you can use an analogue meter (an AVO for instance), you want to look for a nice smooth swing. If it is jumpy it indicates the pot is a bit worn. A digital meter will not show up any jumpiness.

Also, the legend that the pot can be rotated a bit to bring a new section of track into play is wrong. It has a limited mechanical swing and will tolerate very little adjustment. In fact its mechanical swing is almost that of the throttle lever between fully closed and full-speed.

[MikeT]

Fast idle is achieved by pulling on the cable and thus moving the lever toward the rear of the pump....

Hi Jim. Reading and re-reading other threads and the BOL, I don't think that's correct. I think the default is fast idle.

When vacuum is present on one side of the diaphragm, the cable will pull and increase the idle

Again, I think the vacuum (ergo cable pull) has the opposite effect.

...firstly disconnect the vacuum pipe to the diaphragm and feel with your finger for the presence of a vacuum. The idle may fall if the vacuum was present

Again, I think it's the opposite, when vacuum is removed, idle should increase (if originally at normal idle).

So without even testing the electrovalve, I'm pretty sure mine has failed, hence the permanent fast idle. I just can't squeeze my hands in to connect a direct 12v to prove this without removing unrelated parts.

[CitroJim]

Mike,

When I reassembled the pump last evening I had a feeling I was totally wrong

The problem was, I was working part on memory and part by looking at a pump all on its own in a non-running condition and not actually having a "live" car to check on.

So, reverse everything I said about fast idle and it'll be right! Still, there was a 50/50 chance I'd be right

[davek-uk]

If I remember correctly, the vacuum is supplied to the fast idle solenoid first and from there to the a/c solenoid. I think if either solenoid is broken it defaults to open and the vacuum escapes. Test the pump by a direct pipe from the vacuum pump to the fast idle diaphragm. This is how mine is set all the time and I find it works fine.

[MikeT]

Jim; I don't have access to an AVO and I noticed the BOL warns that if removed, the load level sensor requires calibrating on fitment but after marking it's position I removed it all the same to attempt to get at the tracks - no chance It's back on now after disconnecting the battery for half an hour. I Drove 7 miles and all seems fine but the hesistation I was trying to cure was intermittent and not easily replicated.

As for the fast idle circuit, I'm fairly certain it's the electrovalve at fault though it's more a niggle than a dire problem. Right or wrong, you provided the assistance I wanted all the same, thanks.

Dave: On mine, the vacuum pump feeds into a t-piece which provides vacuum for both the EGR and the fast idle systems.

On the fuel pump, the default is fast idle. If the ECU provides power to the electrovalve (which it should once a certain coolant temperature is reached & the A/C compressor is not active), it opens allowing the vacuum to suck the fast idle cable via a diaphragm which moves the fast idle lever back, reducing the revs to "normal" idle.

Therefore, a failed electrovalve will be closed (unless stuck open or leaking etc) and the revs stay high. In bypassing the electrovalve, you are disabling the fast idle which may not be a good idea with A/C.

I have tested for vacuum at the pump and it's good. Both cold and when the engine warmed up, there was no vaccum from the electrovalve though I'm not sure at what temperature it should be actiivated.

[davek-uk]

That's exactly what I have done, disabled the cold start (and convieniently forgotten about the ERG system). I noticed the cold start electrovalve(s) were duff some 4 years ago now and bypassed the whole system as they were reported as being £30-odd each. I haven't had a problem and cold starting, even in the dead of winter, has never been a problem. It depends on the engine I suppose, some will cope whilst others may not. However it's a good way of testing the cold start diaphragm on the fuel pump and is a good short term fix.

I believe the solenoids are cheaper from Peugeot than from Citroen - perfect sense!

[MikeT]

I'll get a pug one then Are they the same unit/colour/fitment etc? If GSF do them at pug prices or cheaper, all the better

[MikeT]

I pulled both electrovalves off and gave them both 12v direct but couldn't hear either of them energise. Is it common for both to fail?

[falling-out-with-my-car]

has anyone found that having the vacumm on constantly connected to the diesel pump has caused smokey running?

regards.
Nigel.

[CitroJim]

It shouldn't Nigel as the vacuum control only affects the idle speed and nothing else... The vacuum diaphragm operates a lever on the pump that acts on the governor.

However, if the vacuum was permanently applied to the EGR valve - thus keeping it open - then that might cause the problem as I believe the EGR valve should only open when the engine is under light load...

Now I have a 1.9TD I can speak with some direct knowledge again...

I must check my fast idle and vacuum operation too... In fact I will shortly...

[CitroJim]

I must check my fast idle and vacuum operation too... In fact I will shortly...

I've now done a brief check and find the cold fast idle lever on mine is jammed in the slow idle position, the cable has been adjusted to be ineffective and the diaphragm pulls in on high revs when cold so there is clearly a problem I'm continuing to investigate...

I'll get the engine up to temperature later and see what changes on the vacuum side...