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My stock fuel injected 1979 superbeetle has starting idling a bit fast. I've checked for airleaks and replaced a suspect hose but the problem hasn't gone away. Just tried a 15 mile drive mostly at around 60mph. The car appeared to be running perfectly except for the slightly fast idle. When I turned off the engine and turned on about 2 minutes later the idle speed was quite a bit slower and was still fine when I reversed the car into my garage. Any suggestions would be appreciated.

Check the cold start injector to see if it's dumping extra fuel in after the engine is warmed up.
Check the idle air bypass valve to see that it's closing properly after warmup.

Thanks Bruce and apologies for my late reply to your message. I have been on holiday with no internet access. I think you helped me out with some engine questions about ten years ago when I was building the engine (still going) for the car I've been driving for the last 20 years!
I remembered I had a new bypass valve and fitted it just before leaving but it made no difference. Have driven around 800 miles in the last two weeks averaging about 28mpg (US) which suggests cold start injector unlikely to be playing up - but still worth checking. Idle stil behaving strangely, mostly too fast, but occasionally very slow.