1988 Carrera quit in mid air.

[witt]

Hi, after nine years of trouble free driving it finally happened:
My well maintained 1988 Carrera Cabriolet with approx. 140k miles on it, let me down during a drive on a nice sunny day.
During a flawless drive the motor just decided to slow down and no longer respond to the accelerator pedal. It kept on idling very rough but pressing the gas pedal did not do a thing. It restarted but still: rough idle and no responds to the gas pedal. No smoke, no weird noises, no smells ,no drama ! Hand operated accelerator by hand in engine compartment, no go.

I am a retired VW mechanic and have serviced the car myself but I am out of my depth with this problem. My plan now is to take a compression test to make sure the motor is sound. Du to the pandemic repair facilities may be difficult to find. The car got towed and is now in my garage.
Any help would be greatly appreciated.
Thank you,
Witt.

PS: tank is 3/4 full

[scotricker]

check the accelerator pedal linkage.
on my SC it just fell off one time, panic for sure,
easy fix , look for pushrods and bell crank connections.
I hope it is just that easy for you too

[GH85Carrera]

If you are a mechanic, it will be something you can fix. Just start reading the threads in this forum.

The classic failure is the DME relay. There are a few hundred threads on the DME relay. The other big issue if the two crank sensors. Then the coil.

You will find a thread that has some other guy that had the same issue, and how he fixed it. The air cooled 911s and as easy to work on as and old air cooled VW. Well, OK, maybe a bit more complex in some systems, but you can do it.

If I can do it and all the other non mechanics can figure it out, you can. And you will bond with the car even more.

Just start with the basic. Fuel, air and fire. Does the fuel pump run and does the fuel pressure build up? Does the ignition have spark. It the throttle opening?

Easy peazy.

[proporsche]

as Glen said..start with the basics..in your case i`d start with the cylinder head temperature sensor...plenty of topics here..take your tine and read up..
Ivan

[jlex]

Yeah, break out the multimeter and test some of those sensors. Also, jumper the fuel pump and check pressure to see if it's trying to go south on you... btw when's the last time you changed the fuel filter? This ought to be child's play for a retired VW mechanic...

[witt]

Quick update: Performed tests following my trusted Bentley manual. Now the car will start as before and does idle only with the Air Flow Meter plug disconnected. As soon as I plug it in it does go back to idling very rough as before and will stall . However I don't have the use of a fuel pressure gauge at the moment.
Any suggestions?

Cheers, Witt

[stlrj]

Fuel pump Kaput! Happened to me too.


Cheers,

Joe
87 Carrera

[gomezoneill]

At 140,00 miles you need to replace the CHT sensor, both reference sensors, Fuel filter . Take a look at the two sensors first. I've seen them with the insulation falling off.

Just a note: you can test the two sensors with a ohm meter.

[mysocal911]

Originally Posted by proporsche

as Glen said..start with the basics..in your case i`d start with the cylinder head temperature sensor...plenty of topics here..take your tine and read up..
Ivan

Most always start with mentioning the temp sensor, which typically isn't the problem!
The temp sensor can easily be eliminated by jumping the two pins at the white connector with a paperclip.

The mention of this basically eliminates the temp sensor;
"No smoke, no weird noises, no smells ,no drama ! Hand operated accelerator by hand in engine compartment, no go."

Read here; 911 3.2 No-Start Troubleshooting

[witt]

Got a fuel pressure gauge now. All readings pressure and all electric tests turn out ok.
dumb question: where is the fuel pressure regulator located ?
I am ready to through in the towel and have the car towed to my mechanic.

Cheers,
Witt.

[ischmitz]

Focus on mixture. CHT, vacuum leaks, O2 sensor, etc.

The FP regulator is connected to the fuel rails. See here: It's connected to the rear of the driver's side fuel rail. The other similar-looking device on the passenger side fuel rail is a fuel pressure damper.

Found the image courtesy of 88-diamondblue:

[han]

Thought these links might help:

MOTRONIC: Fuel Pressure Regulator?

Symptoms of a failed CHT Sensor?

[ian c2]

Originally Posted by witt

Quick update: Performed tests following my trusted Bentley manual. Now the car will start as before and does idle only with the Air Flow Meter plug disconnected. As soon as I plug it in it does go back to idling very rough as before and will stall . However I don't have the use of a fuel pressure gauge at the moment.
Any suggestions?

Cheers, Witt

Check the afm .
Iirc it’s a 0-5v signal as it tracks its movement .

[Mixed76]

Did you check the throttle linkage? Pretty strange to have no throttle response. When you open the throttle, something should change. If the throttle is actually opening, and the engine can't sense air flow or throttle position, it should die from going lean. If it is sensing air flow or throttle position it should do something- increase revs, stumble, something.

Consider blipping the throttle plate/ throttle body at the engine. If that works you know the throttle linkage is bad.

Dan

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[Fairview]

When you said it quit "in mid air", I thought you were talking about this Our pilot Porsche members may remember the Mooney airplanes with the Porsche engine, late 80's I think.

[proporsche]

another basic checking is for you look at the hose clamp on your AFM....on the pic above right to the left of the copper pipe..check all the connection ..could be false air leak if it does not take the throttle..
Ivan

[Walt Fricke]

You can test the air fuel meter, as suggested. Because it is a mechanical rheostat, I suppose there could be a break in the resistance wire. You open the throttle, more air flows, but the ECU doesn't know to increase the fuel. These can also act up if they get oil or crud on them, and can be disassembled to check and clean. But an ohmmeter should show if it is working when you move the flap.

Agree that CHT failure doesn't present this way. The signature here is that it won't go above idle, and you have verified that the fuel pressure is OK. I never had a crank sensor issue with our 3.2, so less sure about that. Easy enough to check the sensors, though.