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Smoke test on the vacuum system turned out fine. Garage did some further diagnostics and noted a wiring issue near the turbo / wastegate. A wiring repair was done in the past and it appears this was not done that great back then.

The wiring repair done by the current garage made no difference and engine is still flat spotting. They now are asking me where I want to go with this given the amount of time they might have to spend finding a potential wiring issue versus the value / age of the car.

Was OK (up to about 60mph anyway) until I got the airbox electrovalve fitted. A £50 part which seems to have caused all this apparently Edit to add: even bought another airbox electrovalve and got that fitted...same issue (that was fitted along with a new swirl flap electrovalve)

Are there any fault codes that pop up when the car flat-spots?

Hi

No fault codes appear when the engine flat spots.

Thanks

Hmm, okay - I'm starting to clutch at straws now..
If the vacuum system is okay ( not sure what a smoke test is and how this works ) and the swirl flap diaphragm is good, then it could be the pipes are the wrong way round.
The swirl rod should pull back the little ball/socket affair on the top right of the engine when it's ticking over, and push it forwards when the engine is revved over 2100rpm - if this is reversed then half the valves are closed when they should be open at higher revs.
As far as I know, and I'm no expert, but the solenoid on the airbox diverts vacuum to the air dosers on the front of the engine, either a cold air feed from the intercooler, or the warmer air from the hot water jacket tucked behind the radiator - I guess if these are the wrong way round then the engine isn't getting the cold intercooled air which would affect performance.
Also, the turbo has no wiring connected ( I don't think ) so I'm not sure what wiring was damaged, but a repair wouldn't have done any harm I suppose....
New fuel filter maybe?
Sadly, I don't know how many things to suggest - it's all time and money which is hard to justify on an older car

Hi

Interesting what you say there about cold air getting to the engine as at 60mph plus (colder air being presented to the engine) there are no flat spots, but at lower speeds there is.

Changed the swirl flap diaghpram and that improved things a bit in terms of no smoke. Still getting flat spots. One other part I am looking at that may be the issue is part no. 1920.GH - intake manifold pressure sensor. Is it worth changing that?

Never known one to go wrong, but I have seen leaks in that area or even the sensor tube broken away from the intercooler in one case.

My 2,2 has a variable vane turbo. It was very sluggish when I got it. Checked everything as you have done with no improvement. Decided to check the turbo so removed it. Found the variable vane system was very sticky due to a buildup of fine carbon? on the vane system. Cleaned it all off, made sure the variable vane was free moving, replaced the turbo and problem solved.

What is the difference between 1628.LQ and 1628.HC valves and is it possible to use 1628.LQ in place of HC?