throttle position pot fault ?

HDI · Post by **HDI** » 12 Jan 2011, 11:38

Over the last few weeks my HDI has exhibited an intermittent problem with throttle control.
Initially it was an occasional hesitation when accelerating after lifting off slightly, then it developed into complete lack of response for a few seconds but then clearing and returning to normal.
Yesterday though, after making a slow right turn and then trying to accelerate along the road, there was nothing when I pressed the throttle, the engine was just at idle, the throttle had no effect.
Turned off, restarted and it was ok for a few seconds then the fault returned.
My destination was close by so by turning off and restarting a few times and keeping the engine speed at about 2000 rpm I managed to limp along and park up.
About 4 hours later I restarted and moved off without a problem but later in the journey I felt the same hesitation problem a few times, got home ok though.
Thinking about it since I reckon it's a faulty throttle position potentiometer as there was just no response to the accelerator at all, like is was disconnected from the engine, but the engine idled !
Anyone else had this type of problem ?

Post by **RichardW** » 12 Jan 2011, 12:25

Not heard of it before, but it does sound like a TPS fault. A new one is £99 so not really, a change and hope thing! Getting it on a Lexia might show you the putput from the TPS to see if it is giving a signal or not. Unless there is someone nearby can lend you a known good one for a test!

citroenxm · Post by **citroenxm** » 12 Jan 2011, 12:42

Thats an interesting one... Mine, though not the same problem as yurs,

When we had the very cold weather, like -3 deg, I noticed on my HDi when I first started the car accelerated VERY slowly, almost though the Turbo was cut out to prevent engine revving when cold... After about a mile it would return to full power and be fine ever since.

Now the weather has returned to normal temertures, 10 deg plus, the problem has gone away...

Id say yours was an intermittent TPS unit, its over under the Inlet pipe and LHM tank...

Paul

HDI · Post by **HDI** » 12 Jan 2011, 16:09

It has seemed to be an issue during this cold weather, so possibly a cold/heat cycle induced fault, or made worse by it.
Anyway, a new TPS off ebay is only around £20 so I'll take a punt on it being that as there is no one with a Lexia near me.

addo · Post by **addo** » 12 Jan 2011, 20:04

I've had some similar issues which ultimately I decided were due to cooling fans.

They sometimes draw far more current than expected and this was upsetting the ECU.

HDI · Post by **HDI** » 12 Jan 2011, 20:09

Won't be cooling fans at this time of year in the UK ! They are reluctant to operate even in the hottest weather. The only time I've known them to operate is on a very hot day in a heavy traffic jam that barely moves.
At one time I was convinced they were faulty such was there inactivity !

addo · Post by **addo** » 12 Jan 2011, 20:12

I'd have thought that on auto defrost (fan speed on auto, position and heat sliders fully right, aircon on) they'd be trying to operate at slow speed.

HDI · Post by **HDI** » 12 Jan 2011, 20:29

The aircon isn't working due to being depressurised, but the fans do work if the AC is switched on.
That wouldn't cause the problem I've been having though.

Post by **RichardW** » 13 Jan 2011, 08:00

It's actually been above 4°C the last 24 hours, and the A/C has run on my car for probably the first time since late Novemeber - despite being switched on all that time

dieselnutjob · Post by **dieselnutjob** » 13 Jan 2011, 11:32

it could also be the brake pedal switches
the hdi has a safety algorithm that if you press the brake pedal it overrides the accelerator pedal, so that the driver can still stop if the accerator pedal sensor develops a fault
there are two brake pedal switches
I think one should be open cirtcuit and one closed circuit with the pedal at rest
the switch states should both swap state when the pedal is pressed
on my 607 the return spring wasn't strong enough to pull the pedal back up and press the switches 100% reliably
I added a supplementary spring and now it's fine

HDI · Post by **HDI** » 13 Jan 2011, 12:47

I'll check that the next time the fault occurs although after scoping around the web the TPS seems to be the prime candidate.
One thing is apparent however, although I haven't noticed before, the engine management light seems to be inoperative, wonder if someone has removed it for some reason or other ?! The car had an intermittent loss of power when I bought it so the owner or garage at that time could have removed it to conceal the problem, tut, tut !

citroenxm · Post by **citroenxm** » 13 Jan 2011, 12:53

Intermittent loss of power could be the ECU sensing too much Turbo boost due to lack of electro valve control (The two valves just by the Cam belt Cover) One controls the Wastegate...

This fault throws a Soft Limp mode, which resest itself with the key off...

Ive had this on a 110 HDi, after swapping the one that controls the Turbo Wastegate, it was all fine again...

Obviously, a Lexia session would show any faults...

Paul

HDI · Post by **HDI** » 13 Jan 2011, 13:33

I sorted the intermittent power issue, it was the boost pressure sensor.

One of these days I will buy a Lexia clone, just a matter of which one ?!

citroenxm · Post by **citroenxm** » 13 Jan 2011, 15:06

The clue is in the line you put.... "Clone" - Means um... all the same..

<runs.... >

Paul

HDI · Post by **HDI** » 13 Jan 2011, 15:10

Are they though ?! I've read differing reports on FCF about the variety about.