'90 BMW 318i - surging throttle problem

Hello,
I have recently aquired a '90 BMW 318i, it has run 230k km and is in pretty decent condition.
However, when at constant throttle - regardless of which gear - I am
experiencing a surging / cycling of the throttle. As a result the car goes faster and faster. Well, not _so_ fast. ;-)
The sympthoms are as if I were slowly pressing the throttle down and releasing it, ending up at a higher throttle setting than previously and repeating it.
I have recently swapped the fuelpump as it died, but the problem was there before that.
Any ideas?
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First thing I'd check for is a vacuum leak. Possibly a bad gasket on the far side of the throttle in the intake manifold.
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Email: snipped-for-privacy@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
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John Burns wrote:

Thanks for the suggestion, I will try to spray some starter help around that area and see if the engine revs higher.
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Nope, that didn't work either. The search goes on. Might it be the airmass meter or could it be the lambda sensor?
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I have had a similar problem but mine also had problems idling...
found out all it was was a loose air intake pipe... near the air filter. seems to be not a great connection...
plugged it back on and perfect!
good luck

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The idle is fine on mine.

Thanks for the tip. I will check these again, the problem still remains and the engine is using around 8.7L/100km. A tad much on a 1.8i I think.
I will take the car to an independent who has a very good reputation and ask if he can plug the analysis tool on the thing to see what might be going on.
Cheers,
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BBO wrote:

Ok, I took the car into a good independent shop and he did a testrun on it. No errors showed up. He then removed the hose on the cold side of the air manifold intake and sprayed some cleaner stuff into the mainfold intake where there is some kind of valve (not sure of the english word, sorry) which was full of soot.
That almost cured the problem, and I will repeat the procedure a few times to get it good and clean.
Apparently it is some kind of idle valve that was stuck causing the surging.
Cheers,
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Yes, the idle control valve. It's easy to remove and clean.
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John Burns wrote:

Yeah, I cleaned that one too, but the stuck valve or gate or whatever it is called was in the air intake manifold. That is the one that wasn't closing opening properly.
After I cleaned and WD40'ied the idle control valve the engine idle became very smooth as well. I like this car. It's fun to drive and tinker with. :-)
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