90 C4 wierd running issue
 

i posted this on the 964 forum, but it doesn't rock like this one does. i haven't got back on this job yet, but any ideas would be helpful, because i seem to have brain fade at the moment. i did a few checks on this car last wednesday evening. cold, it starts and runs fine. after 15 minutes or so, it looses power when driving. no dash lights come on. no throttle response. but it will usually idle roughly if i let it. while coasting along after the power loss, the key can be turned off and on again and the power will be restored for approx. 5 seconds. i can keep driving if this is repeated.
i tried another known good airflow meter, and a new DME relay. it has a very recent oxygen sensor and head temp sensor. haven't checked fuel pressure or flywheel sensor yet. distributor belt is good. has had the airflow meter plug tie-off done, and moving the loom around does nothing. the fact that it gets fixed for a few moments after turning the key off and on is the main clue i think. any ideas appreciated

A long time ago a Carrera guy posted that the contraption under his seat had a frail solder connection in the plug area.

Same routine as yours.

Tony from Mississippi has a slantnose '88. He went nuts for over 6mo taking it to various shops. Then he started it cold and put a heat gun to the flywheel sensor before the engine would heat up and stop.

It immediately stopped.. bingo

yeah, i haven't got back on it yet, but the flywheel sensor is a priority thing. i may be looking at the computer circuit board with a magnifying glass too. i'm just trying to relate to why it fixes itself for a few moments by turning the key off and on again. i can't see the fly sensor of computer doing that, but stranger things have happened.

I just e-mailed Tony all this.

the guy said the plug area wire got hot and opened, then cooled and closed. [Greater resistance would generate heat.] I think he also said it was a vibration sensitive connection area from the plug wires to the pc board?

Fuel pump failing - low fuel pressure, overheating from high current draw, re-cycling the ignition gives a momentary respite....

John - sounds like a DME problem. What other circuit would reset anything at all with the power cycled? I don't think it is a heat issue because a quick power cycle would mean nothing. It almost has to be reseting something in the DME.
I have a known good one if you need it for troubleshooting purposes.
good luck -

hallo
I think too, it is the DME , when turn off it will reset itself .
I had a similar thing with a Lambda sensor , but only in rain . Car did stall or ran very rough , when turned off it ran fine for a few Minutes .

Harald

Hey John,

You gotta screw driver or a road side rock handy?

Bang that DME unit a couple of times and see if that doesn't fix the problem.

Someone very wise that just happened to be in his "Workshop" on a Sunday afternoon once told me this...and it worked. ;)

try the alarm, Kevin

still haven't got back on it, but keep the ideas coming. i think i can find a local computer to test with. wish i had a whole set of them thru the years. i was thinking about the pump. easy enough to do a pressure test.