intermittent throttle response

[helisurf]

Occassionally (about every 3 weks) I put my foot down and nothing happens for about 1 second, occasionally longer, on my 8V 1.9CDTI. Caught it happening with the laptop plugged in last week and only thing I could see in the logged data was that each time the power was delayed, the boost pressure (inlet manifold pressure I think) in the seconds before with foot off the pedal was about 40kPa, and when there was no power delay the boost pressure was 98kPa in the seconds before putting the foot down.
Makes me suspect that the throttle body is not responding properly so I've resoldered the connector joints on the circuit board (couldn't see any crack in the joints but soldered them to be sure). Currently I'm seeing 98kPa boost pressure with foot off the pedal and waiting to see if hesitation stays away.
What should the inlet manifold pressure be with foot off the the accel pedal? Is this car meant to partially close the throttle valve during over-run and idling?

[GazVXLINE170]

Your CDTI being 2004 I suspect the issue is the throttle body soldering joints breaking up and causing the throttle control within the throttle body to think you have ifted off of the throttle pedal. If it is that then it will get worse to the point the engine will cut out on you - dangerous. Have a look at the how 2 for fixing it. I've had it happen to my CDTI 150 (the 120 should be similar).

http://www.vectra-c.com/forum/showth...45#post1338145

It's not a difficult fix but if you took it to a dealer they would want to put a new throttle body on it where a £20 soldering iron and some solder and a bit of time should sort it very well and cheap.

[helisurf]

Thanks for advice but I've soldered the connector joints today as described in the how to (couldn't actually see anything wrong with them) and saw no change.

Its so intermittent that its hard to diagnose but as you say, I'm worried about it cutting out in very bad circumatances.

Not sure if the inlet manifold pressure is supposed to drop at idle with a partially closed throttle valve. This evening the pressure at idle is 98kPa so the throttle must be fully open. If anyone is sure about what it is supposed to do it would help me diagnose if I still have a latent problem that could bite me!

[GazVXLINE170]

Thanks for advice but I've soldered the connector joints today as described in the how to (couldn't actually see anything wrong with them) and saw no change.

Its so intermittent that its hard to diagnose but as you say, I'm worried about it cutting out in very bad circumatances.

Not sure if the inlet manifold pressure is supposed to drop at idle with a partially closed throttle valve. This evening the pressure at idle is 98kPa so the throttle must be fully open. If anyone is sure about what it is supposed to do it would help me diagnose if I still have a latent problem that could bite me!

I am asumming you have checked the usual suspect - the EGR valve? Have you cleaned that out? It can cause the symptoms you describe too.

[helisurf]

Haven't tried it yet as i assumed I'd still get a little bit of "throttle" pedal response even with EGR stuck in the wrong state. Guess I could pass some time over Xmas cleaning it out.

[helisurf]

Too wet to open bonnet today. Checked EGR via laptop. Air mass sensor going up and down promptly when I open and close EGR by software so doubt thats the problem.

Checked sensor logs from a few drives and looks like I get the power hesitation when a DPF regen is going on (exhaust temps over 600C, normally 300Cish on motorway) and thats when I see manifold pressure dropping to 40kPa on over-run so throttle valve must be partly closing under these conditions.

Anyone seen this behaviour?

[DAVIDD88]

It's the egr if I had a new one fitted it something to do with a software update had this on my 1.9 8v

[helisurf]

You reckon I need a software update? and new EGR?
Still not conviced about EGR problem because when I get the hesitation its when going from over-run to foot down at 1400rpm+ and the egr is at 100% before and after pressing accelerator pedal so it wouldn't matter if it was stuck.

[DAVIDD88]

No I reckon its had the new egr without the software update but might be wrong I remember having same problem after getting new egr

[TonyP2020]

Can you also see the Boost Pressure Demand on the laptop??
For example if the demand is 110Kpa, the actual is 98Kpa, and the Brometric pressure is 100Kpa, then the inlet manifold actually has a slight vacuum.

This could mean a air pressure leak or a problem with the turbo.

If it happens when the DPF is regenerating, then overheating turbo is possible.

You could remove the fresh air side of the turbo and see if the turbo spins ok and also see if there is oil in it.
If there is oil then the turbo seals/bearings might be on their way out.

Another thing to check with the laptop is the voltage shown across the Barometric and Boost Sensor's. It should be about 4 Volt. When my barometric sensor failed (2.0DTi not a CDTi) it gave a reading of 1.6V, but it still gave the correct air pressure.

What mileage is the car and what type of driving (town/motorway/etc) do you do??