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'87 3.2 G50 - rough idle/stumble when accelerating

My car seemed to just develop this problem that I THINK has gotten progressively worse. Symptoms as follows:

* Rough idle, either hot or cold. It's idling very low, like 600 RPM, a lot of hunting - nearly stalls (has stalled a couple of times but it's rare) and occasional popping
* On acceleration, there is a hesitation or stumble. It's like how it feels when the engine is lugging at low RPM. It seems that I get through a particular stumble and the engine is OK again... it's hard for me to tell if it's making full power, but at least some of the time, it pulls like a freight train

Some things that have recently been done:

* New cap and rotor. Smoothed out the engine a lot but didn't solve the problem
* New air filter
* 3 tankfulls of gas with a bottle of Techron in each
* Took apart AFM and bent the wiper arm to ride in a new arc. Old one had a couple of bare spots, but I've seen worse in other threads on this forum

I have a new O2 sensor on order, should arrive today. I'll install that and see if it helps at all.

But I'm looking for other ideas. Any ideas on where else I should start?

Thanks
-Glenn

Old 07-30-2014, 11:47 AM
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Just another observation.. the stumble happens at full throttle, too - althought it seems, less frequently. Doesn't that mean it can't be the O2 sensor?

Thanks
-Glenn
Old 07-30-2014, 11:58 AM
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p.s. the car has 234,000 miles on it, 10,000 of which were done by me over the last 7 months, in sheer bliss
Old 07-30-2014, 11:58 AM
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If you unplug the O2 sensor and it smooths out, you will know it's the O2 sensor. It switches to a different mode of control in the ECU. If you unplug it and it doesn't smooth out, it's something else.

Another suggestion is new wires. Also temp sensor. I don't know of any tricks to test that.
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Old 07-30-2014, 12:01 PM
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Ok. That's an easy enough thing to test, thanks.
Old 07-30-2014, 12:02 PM
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Ah!! Full throttle stumbling would indicate it's not the O2 sensor. The "wide open" sensor takes the O2 sensor out of the mapping equation.
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Old 07-30-2014, 12:02 PM
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I had this issue on my old 3.2 - I changed the coil and the plug wires and it went away. Definitely seemed to be ignition related,.
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Old 07-30-2014, 01:35 PM
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+1 on the O2 advice above. I would also change plugs (wires and/or coil?) to go with that new cap and rotor.
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Old 07-30-2014, 01:48 PM
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Another possible clue: There is no fast idle. The pattern of it starting around 1000-1100 rpm and then selling down to 800 isn't happening anymore. Does that mean anything?
Old 07-30-2014, 02:23 PM
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Found the problem! One of the plug wires wasn't fully seated. What boneheaded did that?!?! Oh wait a minute... That was me :-/

Well I just fixed it and took it for a drive, and OMG, what a car. The sound of the engine echoes in my head even after shutting it off... Wow.

Thanks all!!!
Old 07-30-2014, 06:06 PM
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Just not nearly as badly as before. Is it possible the plug has been fouled?
Old 07-31-2014, 05:40 AM
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Not sure what happened with that last post... What I meant to say is that, while it is MUCH better, still a mild stumble happening. Is it possible the plug is fouled?

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Old 07-31-2014, 05:55 AM
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I would just change the plugs. Cheap and easy...and just good maintenance.
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Old 07-31-2014, 06:54 AM
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Change the plugs. Costs what, $20? Check to make sure you have the wonderful Porsche specialty tool first.
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Old 07-31-2014, 07:35 AM
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is this the tool? 1987 Porsche 911 Carrera Coupe - Ignition - Page 2
Old 07-31-2014, 07:53 AM
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sorry, bad link. Is this it? Pelican Parts - Product Information: TOL-SK4490
Old 07-31-2014, 07:56 AM
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they're probably referring to this tool - in your tool kit.

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Old 07-31-2014, 08:54 AM
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Oh. I do have that. Wondered what that was...
Old 07-31-2014, 09:14 AM
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You probably need to check for vacuum leaks, while your back there. A ton of threads on that. If you haven't got the Bentley, you might want to invest in one.
Old 07-31-2014, 10:06 AM
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You probably did this, but did you replace the Fuel Filter?

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Old 07-31-2014, 10:46 AM
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