Scamper

OK, guys, after my trials and tribulations with the ABS ecu (managed to source one local to me) which is now sorted. I have another issue with my 90 C4...

I have a slight experienced surging on part acceleration and a complete cut out twice whilst on the motorway (freeway) luckily i was in the nearside lane.

Anyway I have cleaned the ISV and AFM (does the AFM need to be resealed after opening???) carried out the STB on the wiring harness, disconnected the battery for the night to reset the DME.. but still the car just dies when idling in the garage. I can hear a distinct click sound as this happens.

Only thing I can think of is that the AFM isnt a sealed unit anymore and is drawing in the engine fumes/burning oil from the heat exchangers and causing a problem with the fuel metering???
The o2 sensor is not connected - this was done by my specialist when I some other problems.
Any ideas?

springer3

The only time mine has bucked and cut out, it was an ignition coil going bad. It was sparking internally, and I could hear popping on the radio. The high-voltage was evidently upsetting the DME. I soon had the complete Christmas tree, and full-time "limp home" mode along with random bucking and power drop-outs.

Two new coils fixed the problem. Both old coils ohmmed out fine - a DMM will not troubleshoot a high-voltage electrical breakdown.

elbeee964

Though, from what I learned this weekend () it could be from a wealth of different engine bay sources that go 'click'...

...I'll just stick with your AFM presumption. (Or MAF)
Was the flapper door 'hanging', before, at any spot in its motion? (And what you're hearing is it finally snapping shut -- disrupted air flow -- sudden change to the rich -- computer can't react in time -- 'poof', goes the air-starved fire?)

(You have a stock 'flapper' door mass air flow box, right?)

Scamper

yep stock AFM.

Just checked the coils and did the following;

unplugged coil nearest the front of the car - started and ran fine

unplugged coil nearest the rear of the car - started and ran rough

Shouldnt the engine run the same for either coil unplugged??

elbeee964

Yup.
Could be any of the electrical links common to that 'rough' coil (the coil, its electrical doohicky right behind it, or its coil wire.

After trying that a second time to confirm consistency of that 'bad' coil circuit...

Swap coil wires around, get the same results, and you could eliminate bad wires.
Swap coils around, get a swapped result, and you'd have traced it to a bad coil. [Otherwise, a suspect doohickey. Or a suspect rotor/cap...]

(And then it'd be time to replace both coils [...or both doohickeys.])

Good job. I think you might be onto something!

Edit--
'doohickeys' == Ignition Control Units 1 & 2

Lorenfb

"The only time mine has bucked and cut out, it was an ignition coil going bad."

He's right on. The 964 DME ECM and its associated elements are extremely
reliable with the exception of the ignition elements, i.e. the coils, caps & rotors,
and the ignition wires. These ignition elements can cause the DME ECM to
have strange problems, e.g. stalling, random misfires, and poor performance.
So, always initially focus the troubleshooting efforts on these elements as
exemplified by previous posts on this thread.

darth

Follow the "KISS" rule and try replacing the DME relay first. If that doesn't help start looking at coils, sparkplug wires etc.

Hope this helps
Bill
90C2

Richard Curtis

I've had bucking and cutting out and it was traced to corrosion between the negative (ground/earth) cable and the unibody.

elbeee964

What ground (location) on the car is that, Richard? Up front, trunk? Unbolt, scuff, re-secure?

Richard Curtis

Yes. Battery is located in the trunk. Remove negative cable, clean both ends thoroughly with wire brush, Scotchbrite, whatever. Clean battery post and the cable attachment point on the unibody. Reattach.