'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

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

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

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.

Ok. That's an easy enough thing to test, thanks.

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.

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,.

+1 on the O2 advice above. I would also change plugs (wires and/or coil?) to go with that new cap and rotor.

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?

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!!!

Just not nearly as badly as before. Is it possible the plug has been fouled?

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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I would just change the plugs. Cheap and easy...and just good maintenance.

Change the plugs. Costs what, $20? Check to make sure you have the wonderful Porsche specialty tool first.

is this the tool? 1987 Porsche 911 Carrera Coupe - Ignition - Page 2

sorry, bad link. Is this it? Pelican Parts - Product Information: TOL-SK4490

they're probably referring to this tool - in your tool kit.

http://forums.pelicanparts.com/uploa...1406825638.jpg

Oh. I do have that. Wondered what that was...

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.

You probably did this, but did you replace the Fuel Filter?

i had a completely loose hose clamp on the back of the intake boot that was causing hesitation issues. simply tightening the clamp seems to have cured the hesitation issues - i say that because i haven't had it on the road much lately. first test drive (afterwards) seemed to indicate all was normal again. check all connections on the boot.

I sprayed carb cleaner around the hoses on top of the engine... no changes, no smoke, no impact.... doesn't SEEM like there's a vacuum leak based on that test.

Fuel filter - I bought one to put in, but my mechanic (and others) have said that with fuel filter, it either works or doesn't... wouldn't cause an intermittent problem. Thoughts?

Thanks
-Glenn

Plus 3, 2, and 1. #3 was the one with the loose connection at the distributor.

I nerve I got oil on #1 while removing it.

How do these look?http://forums.pelicanparts.com/uploa...1406903761.jpg

UGH. Autocorrect...

These are PLUGS 3, 2, and 1 in that order. #1, I think I get oil on it while removing it.

Thanks
-Glenn

Before you clean in re-install the plugs, check the OHMs on those and the Cap and Rotor too.

I am concerned you are not getting the Warm Up Idle as you say Fast Idle.

Here is a better way to check for a vacuum leak, driver her around for 20 minutes or up to full operating temperature, leave the car on, place your eBrake then open engine lid and remove the oil cap, if she does not drop in idle you have a vacuum leak and need to locate it. A smoker is the best way to ID the leak. I found my leak behind the throttle body at the U hose. Use a mirror and you can see it too.

BTW, what is your location? maybe a fellow 3.2 can swing by to take a look???

I am in central NJ. thanks

I had similar symptoms on my 964 and it was the MAF. Can't recondition them so you need a good 2nd hand one to try.

Ugh. I think it's a vacuum leak. No, the idle doesn't change when I remove the oil cap. And spraying carb cleaner BEHIND the black right-angle pipe going into the AFM definitely DID bring the idle speed back up. I tried looking back there with a small mirror, but don't see anything obvious.

The front of the right-angle bend plastic pipe has some surface cracking, but it doesn't look that bad to me. I see a hosing coming out the back, going to the oil tank... and of course the connection to the AFM on one side and throttle body on the other.

Is there a common failure point here, that it is likely to be? Any tips for me on how to hunt this down? I'll have to search the forum and see what others have found.

I did change the O2 sensor, and the plugs. I have no idea how old the old ones were, so I am considering this a good idea anyway to change.

Thanks
-Glenn

997Sbeebe - when you say, the back of the intake boot - are you referring to the hose coming out of the AFM?