Date: Wed, 20 Oct 1999 00:19:48 -0700 From: Justin VanAbrahams <jvanabranopsamnet> Subject: Re: 900 Acceleration Bucking
Bob Incorvati wrote: > > My '86 900T (168k) has begun to "buck" under virtually anything but cautious > acceleration. I want to say it is more prevalent when cold (in fact, I > think I just did), but can happen anytime. It seems to limit itself to > around the 2k -2.5k range. Above or below those rpms its fine. > > I seem to recall earlier discussions revolving around a wet or weak AMM. > The car does not go out to play in the rain so operating conditions are > always dry. Weak? It *is* the original AMM. Is there a reliable bench > test? What are replacement options. Or, am I completely off base. More > likely the latter. That is really quite odd... Normal causes for bucking would be an improper air:fuel mixture. That could be the result of a weak or faulty air mass meter, but in my experience these things go quietly and not all at once... you'd have other drivability problems long before it got that bad. Check to make sure your hoses and rubber couplers on the intake tract are in good shape. Since the turbo pressurizes the intake tract, small tears in couplers, weak seals on hoses, or dried out & crusty seals can be blow open, causing a massive vacuum leak that could cause these symtoms. Check the the rubber grommets on the intake manifold to make sure they're in good shape; check all the vacuum lines attached to the intake manifold; check all the rubber couplers/elbows that hold the intake plumbing together for small tears (you'll have to remove them to check fully). Also, since your car is an '85, check the plastic elbow that sits on top of the intake manifold and has a 1/2" or so hose going to the idle control valve - the plastic becomes weak and that elbow will get blown out of the intake manifold - it gets sucked back in when you let off the gas, so you might not notice it. Get some high-temp epoxy (JB Weld works great) and epoxy that bad boy to the intake manifold so it doesn't leak. Let's see... other less likely culprits could be a bad O2 sensor, though like the AMM you'd probably have other issues. Check that there isn't moisture in the distributor housing, and that all the spark plug leads are within spec. Check the rubber o-rings around the fuel injectors to be sure there is no vacuum leak there. Check your timing chain tensioner to make sure it's still properly tensioning the timing chain; if it hasn't been updated to the new-style tensioner, do that immediately anyway. Check to be sure the hall sensor connector on the distributor housing is in good shape - if that connector grounds out, it *could* cause the car to buck, though more likely it would stall. My money is on a vacuum leak... Do the timing chain tensioner no matter what... -Justin
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