CX GTI Turbo jerky off closed throttle..

[white exec]

Weak mixture? What colour are the plugs?

[Zelandeth]

Before you go chasing your tail, I'd check that everything's A OK with the ignition system first. Easy to check plugs are gapped right, distributor cap is in good order etc...

A weak spark can cause problems when you open the throttle, giving bafflingly similar symptoms to fuel starvation. Caused me a month of head scratching that did, and lead to me just about rebuilding and checking every adjustment of it on the Saab when I had an ignition problem...Turned out in my case to be caused by an issue with the rotor arm.

If that doesn't show up any issues, then come back to the injection system.

The K-Jetronic system uses a bizarre system to adjust the fuelling during warmup, and the warm-up regulators can fail if they get full of gunk because filter changes are neglected. Sadly from what I've read they aren't serviceable so replacement is the only option. Correct operation can be checked if you have a fuel pressure gauge and an accurate way of measuring coolant temperature.

Before panicking about that though, go grab a can of carb cleaner and have a good spray around all the hoses with the engine running. If the cleaner gets drawn in through a leak, it will cause the revs to drop.

The idle speed being too slow can cause issues for the system as well. It relies to some extent on a minimum flow through the metering unit and if the idle is too slow it will tend to hunt a bit. If you're adjusting that, worth checking the idle mixture is right as well (you'll need a really long 4mm (I think) Allen key for this). Ideally you should use a CO meter to set it to the book value. I've never had access to one, and on the Saab I've always treated it the same as setting it on a carb...Turn it one way till the revs just drop, then do the same the other way, and stick it right in the middle. Then using my nose I assess whether it smells right. The emission test results at the MOT tell me I'm not far wrong either.

Given you've got a turbo I'm guessing you have quite a bit more plumbing on the inlet side of things, so a vacuum/boost leak has to be a good candidate though.

[wurlycorner]

It's LE-Jetronic, not K Jetronic.
Citroen used at least 2 of the variants of LE-Jetronic over the course of the GTi-Turbo's life, though I'm not sure if that included all 3, or just the 2.

Being an 85 model, this is probably LE1 (these model years have the seperate cold start injector and thermo switch and I think it's only LE1 that had that).

I have 2 of these cars (and 2 series 1's - which have the same injection set up, but worse oem installed spaghetti wiring )