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Join Date: May 2006
Location: San Jose, CA.
Posts: 247
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Bouncing Tach
It just startd happening. Every time the car comes to a stop the tach bounces 2 to 3 times before it settles down to a steddy idle. What could it be? Bad O2 sensor. Is the a way to check or measure? A clogged injector? Or is it something else.
John 1985 3.2 Carrera |
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06-11-2008, 07:57 AM
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It's not just the tach that is "bouncing" it's also the idle. The motor will vrooom vrooom a couple of time before it settle to an idle.
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06-11-2008, 08:53 AM
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Join Date: Mar 2001
Location: Marysville Wa.
Posts: 22,419
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800 rpm on those. much higher, and they can do that. wouldn't hurt to clean the idle stabilizer valve with spray carb cleaner. B12 chemtool works good.
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06-11-2008, 09:03 AM
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1-6-2-4-3-5-1-6-2-4-3-...
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That's not a bouncing tach, that's a bouncing engine.
Just to clarify, because there is a bouncing tach problem which does not follow the actual revs of the engine. 
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'70 911E Coupe, Webers 40IDA |
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06-11-2008, 09:08 AM
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Just to make it clear, my motor is bouncing thus the tach is bouncing also.
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06-11-2008, 09:23 AM
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Join Date: Oct 2006
Location: MYR S.C.
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if it bounces when steady running, check the alternator/ voltage
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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06-11-2008, 10:55 AM
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Monkey Butt Forespin
Join Date: Jul 2007
Location: Cumberland, RI
Posts: 474
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I'm told a rich mixture will cause this. I have an aftermarket chip, have replaced my idle valve, and still does it. Was told it might be the chip, and that going with a Wong version w/ more memory than the 2K would likely smooth out the idle & surging.
"Idle Surge" will yield better results in a search than bouncing tach for your situation.
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Fred Hurder Jr For Tech Questions: '84 911 Carrera Cabriolet (US) Weltmeister Chip, Fabspeed Euro Pre-Muffler, M&K 1-in / 1-out Muffler 22 ERP /29 Sander Hollow T-Bars, Bilstein HD Struts / Sport Shocks ERP Poly-Bronze Bearings (A-Arms & Spring Plates), Stock Swaybars Turbo Tie Rods, '92 C2 5-Spoke wheels w/ 1" adapters, Drilled Zimmermans Yes, I drive mine as much as possible. If it's >32° & sunny, I've got the top down.
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06-11-2008, 12:04 PM
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OK, I have observed a few things. This only happens when the card is hot. Meaning the temp needle is about half way. I goose the gas a bit at a red light and the RPM will bouce a few time, about 5 or 6 time before it settles to a normal idle. I did put some Techron the the tank, thinking it might be clogged injector. If it is running rich, what can I do to fix this?
Thanks John |
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06-13-2008, 07:56 AM
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Join Date: Dec 2001
Location: Venice Beach, California
Posts: 838
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Tighten the intake manifolds.
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06-13-2008, 07:59 AM
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I tighten all that I could on the intake manifold. Everything was snug to begin with. The tempp gauge is almost at the halfway point. The RPM still bouces. Any other ideas??
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06-13-2008, 09:28 AM
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ALso, I check the voltage of the battery while it's running. The voltage looks steady from cold engine to hot engine. I didn't see any voltage fluctuation.
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06-13-2008, 09:47 AM
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1970 Porsche 911E
