1987 3.2 carrera

[simon hole]

i have a problem which has me foxed,the car"hunts"at 2500 rpm in all gears,it is quite violent rocking backward and forward motion similar to kangarooing,this is with the car rolling on a feathered throttle,accelerates straight thru 2500 with no hesitation,
diagnostic shows no problems with e c u ,have replaced dist/cap rotor arm and ht leads,
anyone out there had similar problems,or thoughts what it could be?
thanks in anticipation
simon hole

[ping1957]

Simon, I had almost the same problem with my 87. It was like the car was pulsating at around 3000 RPM's. I'm not sure which of the following corrected the problem, but here is what I did and no more pulsating.

New Cap
New rotor
New fuel filter
New plugs wires
Replaced 1 bad injector

[Fl Ted]

De ja voo all over again
Does it do it only after you've driven a while? (engine up to operating temp)

[simon hole]

fi ted,no seems to do it all the time,even wen just driving off from cold.you say deja vu,wat was your cures,

ping.tried most of your solutions,not fuel filter tho.

other people have suggested drive train

your thoughts?
thanks
simon

[jorian]

Vacuum hoses?

[Fl Ted]

Simon:
How many miles on engine?

[Fl Ted]

Simon: My problem turned out to be the cylinder head temp probe, but the engine had to warm up before it acted up. While I was searching this forum for clues to my"bucking" problem, I came across a thread regarding the Mass Air Flow sensor, or Air Flow, Mass (AFM) which is the silver box that your air filter housing bolts to. A vane just inside this sensor moves in relation to the air mass entering the induction system as regulated by the throttle plate opening. This vane is conected to a potentiometer that has a wiper arm that moves with the vane, thereby providing a voltage for every throttle position , said voltage is read by the DME, which then adjusts fuel mixture accordingly.
Now for the bad part; with use over time, the wiper arm contacts wear through the "film" type resistor element, making its voltage output erratic or non-existant in some or all throttle positions. Since yours is cutting out at 2500 rpm, I'd be willing to bet thats where your engine sent most of it's time, so that section is the most worn.
Now the good news! There is a fix which will cost you little to nothing if you DIY. You'll have to do a search on this forum, try "mass Air flow wiper ". I don'tremember the thread, but I believe it lead to someones website that had instructions and pictures on how to do it.
Good hunting,
Ted

[kepperly]

DME relay under drivers seat!!

Keith Epperly
87 slant nose tyrbo look carrera cabriolet

[450knotOffice]

My Carrera engine did the same thing when it got hot. At very light, steady throttle settings the engine would kind of lurch and hesitate. It was almost as if the engine management system wasn't sure if you were asking for gas or idle. Hence the lurching.

I checked around on this board and tried a few simple tests suggested by some knowledgeable people on this board. I finally decided to take the car to my very competent Porsche mechanic and they had it fixed in a day. They ended up adjusting my idle speed setting, which was mis-adjusted, and reset the mixture. There was also a loose clamp where the Air Flow Sensor (that silvery metal box that attaches to the air filter box) attaches to the big rubber elbow shaped pipe. It was so loose that if one pushed lightly on the box, a big air leak would develop and cause my engine rpm to pick up considerably. I tightened the clamp.

I would suggest that even though most of us like to do most of our own work, when it comes to the complex engine management system that this car has, we should probably leave the tuning and troubleshooting of that system to the pros who are equipped and trained to root out these sorts of problems.

On the other hand, if you've got time on your hands (like days or weeks), go buy a book called "Bosch Fuel Injection and Engine Management" by Charles O. Probst and methodically troubleshoot your engine yourself. Note, however, that you will probably not have the required diagnostic tools so you may end up spending money replacing components that are actually fine. That's why I suggest a good shop do the job. They'll get right down to the heart of the matter and will replace or adjust only those components that actually need it.

Good luck to you.

[simon hole]

thanks for the advice,give me plenty to think on ,will let you know wat the state of play is later,
simon

[fastpat]

Originally posted by Fl Ted
Simon: My problem turned out to be the cylinder head temp probe, but the engine had to warm up before it acted up. While I was searching this forum for clues to my"bucking" problem, I came across a thread regarding the Mass Air Flow sensor, or Air Flow, Mass (AFM) which is the silver box that your air filter housing bolts to. A vane just inside this sensor moves in relation to the air mass entering the induction system as regulated by the throttle plate opening. This vane is conected to a potentiometer that has a wiper arm that moves with the vane, thereby providing a voltage for every throttle position , said voltage is read by the DME, which then adjusts fuel mixture accordingly.
Now for the bad part; with use over time, the wiper arm contacts wear through the "film" type resistor element, making its voltage output erratic or non-existant in some or all throttle positions. Since yours is cutting out at 2500 rpm, I'd be willing to bet thats where your engine sent most of it's time, so that section is the most worn.
Now the good news! There is a fix which will cost you little to nothing if you DIY. You'll have to do a search on this forum, try "mass Air flow wiper ". I don'tremember the thread, but I believe it lead to someones website that had instructions and pictures on how to do it.
Good hunting,
Ted

AFM = Air Flow Meter. The current ne plus ultra article on it is: http://frwilk.com/944dme/afm.htm?session=b9FGjNcXME8ophyKIiu5YWUMnT

[simon hole]

well replaced the dme relay this morning ....no difference,

fi ted... i hadn't really realised before ,but mine starts playing up more when up to temp,.so your route next i think ,though i'm amateur at diy so i'll probably leave that to the pro's

thanks for your help chaps,keep you posted

simon

[simon hole]

after much searching in the uk for a new sensor,only porsche gb had one
£700.00!!!! so i got one from a breakers yard, fitted yesterday and its fixed the problem,so many thanks to everyone who helped..

[greglepore]

Make sure its the updated sensor with the ground. They're available in the states for around $50.

Generally, DME relay failures are related to the engine cutting out completely on a random basis, or no start/car died.

Crank sensor failures result in both no spark and no fuel as the DME needs imput that the motor is spinning to activate the fuel pump and to time the spark, but can be intermittent and hard to diagnose.

Cyl temp sensors give weird symptoms, usually when car is at either temp extreme, but usually when warm. Often car stumbles under very specific load/rpm combos and runs fine elsewhere. When mine failed, it would stumble under high load/high rpm (almost like a fuel pump or filter issue) or, oddly, under very high cornering loads on throttle pickup (really scary in a 911).

[sp_cs]

Originally posted by simon hole
well replaced the dme relay this morning ....no difference,

fi ted... i hadn't really realised before ,but mine starts playing up more when up to temp,.so your route next i think ,though i'm amateur at diy so i'll probably leave that to the pro's

thanks for your help chaps,keep you posted

simon

Simon

I'm about to replace the AFM on my 3.2, similar symptoms to what you've described

Can I ask which vendors you tried to obtain the AFM from? (I'm UK based too)

Thanks

SP

[ZOA NOM]

Here's the thread from awhile ago.

AFM flat spot

[sp_cs]

Originally posted by ZOANAS
Here's the thread from awhile ago.

AFM flat spot

Thanks for that Zoanas

Gotta be worth a go prior to messing aroud with the AFM

Cheers

SP

[2.7RACER]

700 Pounds for a AFM. I need to get into the AFM business. The typical failure mode is the film potentiometer wears thru and sends the wrong voltage or no voltage to the DME at certain positions (read RPM's).
If you are electrical confident you can check the pot by connecting to the AFM with a meter and moving the little door from closed to open. As with any pot, the resistance should move SMOOTHLY up and down as the door is moved. A bad pot will jump around, especially at the worn spots. This jumping erratic voltage into the DME will result in the wrong signal to your injectors, causing surging, flat spots, etc.
Rebuilt units should be available from the US for less than $300. Pelican may even have a source. Check there first.

[ZOA NOM]

My wrench had a source in LA. Two-day turnaround. It came back clean as a whistle with all new innards.

[Nine9six]

I bought an AFM from a fellow Pelican for $75...Works like a champ!