Still Chasing idle issue - any further thoughts

[mep12345]

As in title and seeking any further wisdom.

Done so far - todays job was double checking the camshaft timing which is correct as you can see in the picture below





The ruler runs through the middle of the camshaft sprocket bolt

1. Checked camshaft timing
2. Set timing (by garage as well as at home)
3. Sorted several vacuum leaks (rubber hose to rocker cover, 2 leaks on induction pipework)
4. Replaced all other rubber hoses with silicon just in case
5. Removed induction manifold and re-fitted sealing with a silicon sealant as well as gasket
6. Checked all electrical connections
7. Swapped ISCV with my spare - no effect
8. swapped throttle pot with my spare - no effect
9. Followed the car mechanics guide except for checking voltages as I don't have the fly leads to do these with the engine running without breaking the insulation and don't want to do that.

Other than the idle issue the car runs fine, has plenty of power and the rectification of induction leaks has brought the idle down to 1200rpm but now the car idles at 1200rpm (before rebuild was around 950rpm) all the time and when hot it doesn't return straight to idle following any revs being applied. Instead it returns to idle revs to 1200rpm and hunts between these two figures for 2 or 3 times before settling at 1200 rpm. When steady idling it was also occasionally hunt between 1200 and 2000. When cold the hunting issue is not there so appears heat related.

Any ideas from the gurus before I decide on taking it to the local motorsport garage?

Mark

[mep12345]

Griffinr said:

When I had idle issues I found that the throttle was partly open. The throttle should be completely shut at idle as the idle control valve supply's the correct amount of idle air. Mine had been set to idle on the throttle when I first bought it so when you took your foot off, the idle air valve opened and it held about 2000 rpm. The ECU then took a few seconds to try to correct the idle speed and it would slow down a bit.
Rob.

Thanks, But have checked this - it is one of the early steps in the car mechanics article and I can confirm the throttle does fully shut when the accelerator pedal is allowed to return to the null position

[mep12345]

Norm,

If you could forward me the electronic instructions that would be good please. My fault code reader shows nothing though. Haven't done the easy start (or brake cleaner - someone else suggested) test yet so will do but the idle surge makes this difficult as engine note changes without this when it is hunting.

Certain it is not the servo as the servo holds a vacuum (is also fairly new - under 3 years old) and the hose to it has been replaced with re-inforced silicone during this fault finding process. You can test vacuum in the servo by stopping the engine and after 60 seconds twisting the non return valve, there should be a noise of air leakage into it - if nothing it is definitely leaking if there is it may be ok, but as my vacuum holds up for over 5 minutes I am sure this is fine.

The good thing is at least the car is drivable if annoying when stopped and idling so I have the smile back with an occasional grimace

Thanks all

Mark

[mep12345]

kev b said:

What sort of injection system does your engine use?

The Bosch L-Jetronic System. I have a workshop manual for this but it doesn't help that much with this fault, has been excellent before though

[mep12345]

ukflyboy said:

I haven't personally, but the previous owner did and he has put in a new servo and hoses too. All the same I'll give it a go this weekend to rule it out. I might look at putting in a 'new' ECU at some point to completely rule that out too, but all indications are that they are pretty bullet proof, so sadly not likely to make a difference.

Tried that with a different ECU that I borrowed, no change. Also I could never track down where the diode was and stopped looking when I found somewhere on the internet that the diode was incorporated into the ISCV on later models.

Still lurking and interested in answer to this if it ever gets sorted, I'll even keep an eye from Washington when I move there in the summer

Edited by mep12345 on Friday 27th November 16:33

Edited by mep12345 on Friday 27th November 16:34