3.2 Problem

[pmax]

If it runs fine at any rpm other than 2200 rpm, I highly doubt it's your DME.

What mph are you running at ?

[sf911]

The problem appears in all gears but is most prevalent in fifth . It is hard to explain , but it happens when I apply just a [hair] of throttle , like a half an inch .
5th gear / 2200 RPM / No Load . A little more throttle or a little less throttle and the bucking goes away .

[proporsche]

sf911 ...you drive in 5th at 2200 in 911???that cannot work, no wonder you are having a problem;-)

Ivan

[Chuck.H]

To answer your previous question, yes any year 3.2 DME will run your engine.

If it only happens at 2200 RPM, in both uphill and downhill tests (wildly different loads on the engine) and you can rule out the DME, you may want to swap out or readjust the speed sensor.

I have a spare DME with a weird problem, may be similar to yours -- with the same software as my primary DME, it has the occasional (every few hours) hesitation during acceleration. When I looked at the signals with an o-scope, all the I/O has spikes that mimic the coil firing. I'm surprised the car even runs with this much signal noise, but it does and I drove across the country with this DME. Haven't had time to look at it any further...

Chuck.H
'89 M491 Targa, 439k miles

[proporsche]

Hi Chuck..are you thinking maybe for the OP spark plugs wires arking?
Ivan

[pampadori]

how does a 3.2 motronic handle decel fuel cut? Does it just look for the idle throttle switch or is it looking at the AFM too?

Thats where my mind went. Sounds like it thinks you are completely closed throttle.

[steely]

Originally Posted by proporsche

sf911 ...you drive in 5th at 2200 in 911???that cannot work, no wonder you are having a problem;-)

Ivan

my initial thought (post) above too, it does seem low to begin with, but I guess it's doable. I was driving today and kept forgetting to try.

Originally Posted by pampadori

how does a 3.2 motronic handle decel fuel cut? Does it just look for the idle throttle switch or is it looking at the AFM too?

I thought it was just the idle switch.

I would think it wouldn't be restricted to just that rpm he is seeing it at, which led me to AFM but he ruled that out.

Slop in the throttle linkage?

[proporsche]

Steely..just looking at the gauges if you will be in the 5th at 2200rpm isn`t it below 60 M/h??
Ivan

[sf911]

I just got back from a drive and she started bucking as I described before ,
2200 RPM / 5th gear / 56 MPH / No Load on throttle . To me it feels like electrical power is being cut for a milli-second until I change the position of the gas pedal . If I accelerate through 2200 she runs great . On a side note , when do you guys use 5th gear ? Or is it reserved for anything over 70 MPH ?

[Rodsrsr]

Originally Posted by sf911

I just got back from a drive and she started bucking as I described before ,
2200 RPM / 5th gear / 56 MPH / No Load on throttle . To me it feels like electrical power is being cut for a milli-second until I change the position of the gas pedal . If I accelerate through 2200 she runs great . On a side note , when do you guys use 5th gear ? Or is it reserved for anything over 70 MPH ?

2200 rpms in 5th is chuggin along. Im beginning to wonder if the problem is simply the need to downshift. These motors are happy in the 4K and up range.

[proporsche]

sf911..you got it;-) 5th gear anything above 75mph.....that will solve your problem..
The rpm in 5th is really slow.When you drive anything between 3000 -5500 is your mark you should be using...street driving.to get the best out of your 911 power..and control

Ivan

[Chuck.H]

Here in flat Florida, I drive in fifth gear at anything above 45 MPH unless I need some powa... (I think the upshift light comes on at 40 MPH). Let's not mask the problem just by downshifting!!!

Have you checked your idle switch for proper operation? It's a little complex, the throttle linkage needs to move and open the idle switch before the throttle plate actually moves, IIRC.

When the idle switch operates, the DME switches from the 2D fuel load 'map' to just an idle/RPM table; if your idle switch is not working correctly it will not transition between the two tables at the right time.

@proporsche, I don't think this is a spark plug arcing problem, but sf911, you can always run your hands over your wires at idle to look for arcs (not for the faint of heart, but it works!).

HTH,
Chuck.H
'89 M491 Targa, 439k miles

[sf911]

Thanks Chuck , I , like you , will rev the s%&t out of my car when I need to , but for cruising around in traffic I don't see the need to race when I can be more comfortable . I will double check the idle switch adjustment tomorrow morning .

[bbdhull]

How old are your wires?
I had similar symptom but at around 3000 RPM.
I check and cleaned all 6 , still doing the same, then, changing the plug wires did the trick.

[proporsche]

Hi Bruno, we have already asked about it ,let`s see what will come up;-)?
Ivan

[ant7]

Small air leak in either throttle body, or pipe work ?
Also, make sure your ECU octane switch is in the correct position for the fuel you are using.
Hope this helps.
A...

[stlrj]

If your air flow meter is adjusted properly you should be able to drive it in 5th at 2200 rpm without any problem. I know I can lope around town as low as 1200 rpm in my 87 all day without a problem but only after I had my AFM set up properly.

Cheers,
Joe
87 Carrera

[pmax]

Originally Posted by sf911

I just got back from a drive and she started bucking as I described before ,
2200 RPM / 5th gear / 56 MPH / No Load on throttle . To me it feels like electrical power is being cut for a milli-second until I change the position of the gas pedal . If I accelerate through 2200 she runs great .

Rule out your AFM ! Take it apart or if that's not an option, perhaps you can find another gear/rpm combination which exhibits the same stumble and confirm it's the AFM.

Not my thread but this looks applicable.
3.2 engine stumble/miss

On a side note , when do you guys use 5th gear ? Or is it reserved for anything over 70 MPH ?

Try 85

[stlrj]

Originally Posted by pmax

Rule out your AFM ! Take it apart or if that's not an option, perhaps you can find another gear/rpm combination which exhibits the same stumble and confirm it's the AFM.

Opening your AFM is futile unless you have sufficient experience understanding how it works that, in my case, has taken me decades to come to terms with.

To put it into perspective, trying to adjust an AFM online is like learning how to do a root canal after a 5 min youtube video .

Lots of Luck,

Joe

[sf911]

[QUOTE=pmax;9991294]Rule out your AFM ! Take it apart or if that's not an option, perhaps you can find another gear/rpm combination which exhibits the same stumble and confirm it's the AFM.

Not my thread but this looks applicable.
3.2 engine stumble/miss

Thanks for sharing the thread pmax , I changed the wiper track last week but this time I will clean it . I'll let you know how it works out .