DME? engine died @idle, rough at ~3K in gear when accelerating
 

Guess it's my turn to git bit by the DME bug. Or so I think.

Driving home today; engine's warm, been going about 15 miles, when I notice accelerating away from a stop light there is heavy hesitation when applying the gas. It gets worse, the higher the gear, but is completely absent when revving with trans in neutral. Next thing you know, engine dies, all warning lights on.

I coast to parking spot, restart; rough hunting, then dies. I limp home, keeping foot on gas at stoplights to keep from dying. Same hesitation and a sort of howling noise from engine compartment if I attempt to flog or floor the gas; this is in 1st through 5th. When I get home and park, then restart, engine dies immediately.

One hour later: car starts and idles more or less normally. Haven't tried to drive it yet. Consulting Streather's volume, I originally suspected failure in DME relay R41. He says to test:

Not sure how to make my own jumper lead. Anyone done this? Moreover, not sure it's actually R41, now that car seems to start and idle fine 1h later.

One other factor: problem started almost IMMEDIATELY AFTER a fuel stop. Sure seems suspicious. But wouldn't car run rough, no matter whether in gear or not? Seems to wind up and roar just fine when drivetrain disengaged.

I have vent kit and dual distributor assy was rebuilt/belted just over a year ago.

O2 sensor? Resonance valve? (don't even know what that is) Idle speed control valve or microswitch? (Idle control replaced 1.5 yrs ago). Just looking at Streather's troubleshooting list.

Gonna go for a short drive soon and see if problem persists. Thanks for any advice in the meantime!

You said your dual distributor was rebuilt in the past year, but your symptoms sound very similar to what I experienced with a broken distributor belt. It might be worth pulling the secondary distributor cap (lower, left) and checking the belt which you can just see inside the bottom of the distributor.

The jumper is just three short (couple of inches) pieces of wire twisted together at one end with male spade connectors (Radio Shack) on the other. They get plugged in to three of the pins where the relay goes. If this works don't leave it in after the test drive as it drives power to the fuel pump without the ignition on.

Good call on visually checking the secondary cap; Streather mentions that you can see belt status by looking in there and although I'd hate to think I blew a belt this soon, I should rule it out.

Just drove again, idle is ok at first, gets worse as warms up, power is quite jerky at 3-4K in every gear.

Mshobe

Sounds like fuel delivery issue. In otherwords, not enough fuel is flowing while under load yet enough fuel is being delivered under "no load". Suspected parts could be clogged fuel filter, marginal fuel pump-dme relay flacky. For a temporary jumper and only temporary - paper clips .

Hope this helps
Bill
90C2

I would suggest strongly that you check the switch at the idle return location.

My car ran like crap because my switch was not connecting with the lever. A minor adjustment and my car flattened right out. Same exact symptoms as you have described.

Since you said that all warning lights(christmas tree) were on, I would not eliminate the possibility of stray voltage, bad ground, or coils.

update: popped secondary distributor cap, visually inspected belt, and it's both a) there and b) looking pretty new and clean (as a 1yr old, vented belt should). C4 still runs like hell, as before. Now I also notice shuddering/lugging in first at what used to be a good idle crawl (i.e., an "up-the-driveway" setting).

@massguy: i like a new theory; I'll have to check this out. This is the idle speed microswitch atop the throttle housing? Not sure what physical lever/switch connection I should be looking for, however. I'm happy to upload a photo of what I think you're talking about if this helps.

@newsboy: I'd agree, but the only time that happened was when the engine killed itself at speed the first time I experienced this idle issue. It hasn't happened since during any of my test runs, in which the throttle exhibited all the aforementioned bad behavior under load, and I've managed to keep the engine running the entire time, often by goosing the gas at idle. (It's definitely a problem confined to idle instability and throttle application under load, so I'm starting to like the switch as a culprit.)

(and, continued thanks for everyone's ideas and suggestions!)

Always suspect the simple things first. I had problems similar to this several years ago. I removed the negative battery cable and cleaned the connections both at the battery and the unibody. Problem solved. I'm not saying that this is your solution but certainly can't hurt. I've also noticed similar corroded ground connections with other German cars.

There are two microswitches off the same harness. One goes to the side of the engine and the other goes into the throttle linkage. My car just needed to have the switch nudged forward a bit so it could be activated.

My car ran terrible until I found this and corrected it. For me it was an easy fix in the end. I have also since done some maintence work in an effort to have a fun season with my buddy.

check out the info in this thread, might help...

https://rennlist.com/forums/964-forum/298321-964-hesitating-tale-of-woe.html

You said this happened almost immediately after stopping for gas. Bad gas? Were you on empty when you filled up? Probably not the cause, but certainly should be considered as this was one of the last events you performed prior to the car acting up.

try to run the car on 1 coil at the time,(disconnect plug below), if the car runs smooth on either but not both, then you need a new coil. i am 95% sure thats your problem
good luck

+1 - bad coil

and always keep a spare DME relay in the glove box... making jumpers out of pape clips just gives me the chills.... easy and cheap enough to have a few relays available in case something fails. I keep a DME and FAN relay in the glove box just in case...

everybody: thanks for throwing in! This board is indispensable. I'm definitely ordering a spare R41 relay just because (using the new 993 part no. Adrian recommends, of course). At least I'll have that as a backup for when the original part finally fails. Could even still be to blame here.

@everyone else on board the 'bad coil' train: This seems like an easy test so I'm going with it next.

@AB-Oz: thanks very much for sharing the old thread. The AFM harness TSB is worth a look. It's hard to tell from those diagrams exactly where everything is, but once I get a chance to look at this in daylight (probably this weekend) I'll rule out the TSB case as well.

Aside from earlier work: The distributor cap wire terminals are REALLY difficult to remove. I ended up using variable grip locking pliers to pull 'em off. In fact, it took so much effort I was concerned I'd pinched them (but they appear to be fine). I assume they're designed to use such a deathgrip on the cap, along with their rubber sleeves, to be completely watertight and vibration-proof.