[Engine] Hesitant to pick up from idle

[Chocolate teaspoon]

I have a 57 Reg 1.4 petrol van with 100000 miles on the clock. It runs fine above about 2000rpm, but idles poorly when cold and hesitates when the pedal is pressed when idling.
I have been trying to sort out this problem for a few weeks, although I think it has been there for about 1000 miles, slowly getting worse.
It starts first time from cold and runs well until the revs start to drop after about 10 seconds. Then it behaves in the way the old choke-fitted cars did when the choke needed to be pushed in a bit.
It needs throttle applying to start when hot, but starts straight away when that is done.
When up to running temperature it goes as well as it ever has done (thanks to the new injectors I suppose) but the hesitation from idling is still detectable.
It doesn't smoke at all, but the inside of the tail pipe is darker than it should be.
I haven't been able to do a fuel consumption check because of all the work done with the engine idling.

I have replaced all the plugs and injectors. Also the coil pack.

The local garage did a compression test, and all cylinders showed 200 to 205psi, which is a bit high I think, but they are all close in value.
They did a leak down test, and all were in the range 20 to 25%. Nothing came out of the exhaust, inlet or other cylinders so I believe the bores/rings are worne, but not disastrously so. The tests were done with the engine at running temperature.
They said it would pass the MoT emissions test.
The oil has been in there for about 5000 miles, is still clean and never needs topping up.
The cooling water never needs topping up.
The engine light never comes on, but I have a Launch 529 code reader which sometimes shows a pending fault code P1327. This is a manufacturers specific code but an internet search to find what it means comes up with things as different as oxygen sensor faults, clutch problems and injector rail problems.

Before I start buying a new oxygen sensor, throttle body, accelerator pedal etc. I wonder if anyone has any suggestions?
Or is it just those worne bores and I should accept it?

[oilyrag]

Have you changed the air cleaner - with higher mileages oil mist can clog the filter (and mice can get in too!). Also an oil droplet can form on the sensor in the throttle body.

[geoff]

Naturally the air cleaner is good ?

I'm not up on modern petrols being old school with carbs points and positive earth but ....

What about the silly things like air leaks at manifold to throttle body ( nip up tight rather than remove ) or if there are any rubber hoses eg vacuum are they in decent order ?

Leaking exhausts will often give mixture and running issues especially when " on choke " or whatever the modern equivalent is ?

With your leak down test - nice to see someone do the thing these days !! - I'd say that the percentage would be in line with the mileage covered and whilst possibly a touch lower than hoped for I'd say not really an issue, the joys of efi etc should iron the variables out.

I take it the vehicle is a " keeper " from your description and the spending so far.

Do you drive like a granny, if so then best to give the car some work to do and drive a bit harder so the emissions sensors get a decent clean off - funnily enough my garage said the same to my grandson at the mot and he lapped it up from them, didn't believe me though, lol !

I'm not one to spend to diagnose but if I was to speculatively spend I'd try and think back to the mot and recall the emission figures and then ( maybe ) buy a new oxygen sensor. Once done I'd then regroup and live with it for a while before spending again but thats me.

Good luck and keep us informed of the outcomes it sounds interesting as a forum reader.

edit : I see oilyrag types faster than me

[geoff]

What are the valve clearances like ??  Are they shim or screw adjust ?

Also when was the timing belt done last ?

[geoff]

Just had a quick look : 1.4 petrol uses traditional screw and locknut adjusters so an easy job and well worth checking as clearances have a major influence on running, should be quick and diy too which is a bonus !

[geoff]

Just a thought are you using E10 petrol now rather than the older style E5 petrol ?

Perhaps the higher ethanol ratio is giving you a problem ?

I'd try running a tank of the " Super " petrol to see if it helps, if it does you'll have your answer virtually for free.

[Chocolate teaspoon]

Just a thought are you using E10 petrol now rather than the older style E5 petrol ?

Perhaps the higher ethanol ratio is giving you a problem ?

I'd try running a tank of the " Super " petrol to see if it helps, if it does you'll have your answer virtually for free.

Just back from a holiday (hire car!). The air cleaner is good. I checked the tappet clearances as suggested. All the exhausts were about 0.4mm as per spec, but 2 of the inlet were closer to 0.4mm than the 0.2mm they should be. But adjusting them has not solved the problem. The timing belt and water pump were changed at 70000 miles as I am paranoid about that. I have always used the cheapest unleaded, but I shall try a tank of the expensive stuff. There are no inlet air leaks that I can find and I am sure the exhaust is fine. Thinking about it a bit more, I wonder if the throttle position pot is at fault on tickover? Sadly it can't be replaced so it would be a new, or secondhand, throttle body.

[geoff]

Good update shame no further forward at least it sounds like the vehicle is very well cared for.

[oilyrag]

Poking and hoping on this ......do you have a fuel filter and has it been replaced recently, and did the garage check the fuel pressure?