Well, I would say that at the end of anything I"ve worked on, never had doubt on cam timing. If tests result in you questioning cam timing, the solution may be found there.
You say it gets worse when it goes into closed loop, have the oxygen sensors been replaced recently or damaged? What makes you think it is cam timing? Have you checked spark on each cylinder, maybe it is part on the electrical system breaking down when hot? Are the vacuum hoses ok with no splits or leaks or blockages?
I second checking for cam timing. Are you sure it's correct? also, when running use one of those laser thermometers to check the temperature at each exhaust port, right at the base of the header. Example, If you're getting 300 degrees on seven and of them, but one only shows a hundred degrees. That will show your problem.
Yes, it could throw a O2 sensor heater inop code, slow signal code, non-signal code, or some other O2 sensor code.
Just a small update. I gave up chasing my tail and pulled the engine. Again. I double check and found the timing is spot on. I also found that I must've pinched the fuel breather hose somewhere sufficiently to break the pipe. So, I've effectively been running with an air leak into both plenums. I just couldn't easily see it with the engine in situ... As its a hard plastic line, I'm guessing there's a fair amount of vacuum running through it, so I've ordered a replacement which I shall then fit and re-install the engine (hopefully next week). Thanks to everyone who has helped with input and advice. Hopefully this should sort it out.... Bloody cars!
Hence my response. Intake manifold leak!!!!. The issue was definitely a leak related issue. Glad you found the problem. Sad you had to pull the eng.
Yup, good shout. What threw me was that unplugging all the plenum hoses one by one made no difference. It never occurred to me the break / leak would be elsewhere in the pipe... And as always, I find every day is a school day.
Looking back that could may well have been the answer you needed. It made no difference! These cars are made to test us. By geez I have had my fair share of gremlins. Mine hase been fault free for quite a while now but just don't get time to drive it. Hence the reason it's on the market.
It's awesome you found it. How it arrived at a "timing problem" is mystery. The good news is pulling it allowed you to see the issue so all's well that ends well! A good tip is to spray starter fluid here and there and see if it changes, it's a great way to find a leak like that as the leak will suck it up and you'll hear idle surge etc. Now go enjoy!