911 switches to "jiggle" mode with no power without obvious reason

[matomorizo]

Hey guys,

anyone any idea what this might cause (see video https://1drv.ms/v/s!AlpMYqK0RFLIhbYWMH1bAwUXdgGSCQ).

It happens during a ride, sometimes during still stand. The motor swiches to this "mode" where idle is very unstable and throttle leads to a something like "flooding" (no power, no throttle reaction). and usually after a few minutes it vanishes and I can continue my ride.

Last year we did a big checking marathon (see here I want YOU to solve this problem ;) 911 3.2 '85 just doesn't want to start anymore) where we found the ECM to be faulty.

It somehow looks like a slack point or loose connection, but I don't know where to start looking for it.

Maybe again the ECM?

I already checked: Idle valve, air flow, air leakage, DME relais, fuel pump, fuses. Also the Ohm values at those components are ok (in the jiggle mode). iginition system and fuel injection had a major rebuild last autumn. all relevant sensors were replaced as well.

Anyone had this problem before or advise how to tackle this issues?

Any help is welcome....

Thank you, guys!

Best
mato

[T77911S]

video did not work.

I assume the idle starts surging or hunting?

check throttle position switch.

[T77911S]

O2 sensor wiring/sensor

[john walker's workshop]

Disconnect the O2 sensor plug and see if it still does it. Ohm the plugs for the crank sensors. 950 +/- between the lower 2 terminals of the 3 in the black connectors. Ohm the idle switch at it's plug for open/close.

[matomorizo]

@T77911S: Thank you for your help. Throttle switch is ok.

@john walker's workshop: Thank you. Will Check O2, cranks sensors and idle swith are ok.

I will check the O2- sensor and wiring by the end of the week and let you know about it.

Yesterday I found that the mode disappears after playing with the wiring in the trunk area. I am wondering if there might be a faulty connection from the fuses to the fue pump which might cause this?

best
mato

[T77911S]

spin all the fuses in the holders.
wiggle wires with engine running

[T77911S]

check dme relay,

[matomorizo]

That is my work load for the weekend! Thank you very much, indeed! I'll keep you informed.

[matomorizo]

Hi guys!

Problem solved!

Again, a faulty ECU! there was humidity inside which you cannot remove. Not uncommon in targa and cabrio versions...

Thanks again for your help!

Best
mato

[pmax]

Originally Posted by matomorizo

Again, a faulty ECU! there was humidity inside which you cannot remove. Not uncommon in targa and cabrio versions...

The ECU can be opened up, so I'm puzzled why the humidity can't be removed.

[T77911S]

that's not a common problem or else it would be a common fix on here. never seen it.