Sudden rough idle & Hesitations after parked overnight!

[Beachdrifter]

Hi all,

I seem to be posting a lot lately, as I am getting gremlins recently.

So here is the major one I am dealing with. Last Friday 4/8 I drove it on a 30 mile or so trip, and every time before that, the car drove, idled, and accelerated as it was intended to.

I left it parked overnight outside, then Saturday morning I go to start, at first seems normal, then suddenly out of nowhere the car begins to chugg chugg, shake shake, and sound like just rough overall. When i give it gas, there is a little hesitation , and then when I turn lights, AC, fans, when I accelerate, the engine really begins to hesitate and bogg down.

The idle maintains ~700 RPM, in the sense, but the engine definitely feels off.

I've checked historic posts on similar conditions and can't quite pin point a similar situation, so I am posting this.

Just some background on my car and parts that may come to mind:

-New Delphi fuel pump over a year old
-New 02 sensor installed after this started happening -- apparently had no impact
-New alternator as of last night, but did not affect anything.
-Test/swapped all ECUs with known good ones -- had no affect. So I assume my Lambda, Idle, and ignition ECUs are working as intended.
-Test/swapped rpm relay, lambda relay -- had no affect. So I assume my relays are good.
-Test/swapped ignition coil -- had no affect. So I assume that is good.
-Checked idle speed motor is buzzing, checked frequency valve is buzzing, checked WOT switch is not sticking, checked idle speed switch is engaging. All seem good.
-Hooked up a dwell meter, besides doing a slight adjustment, I see my meter cycling up and down around the 20 mark (40 for 4 cyl reading), so I assume the fuel mixture is good and the cycling indicates lambda is working with 02 sensor and freq valve?
-Checked bulkhead connections are tight and cleaned.
-Battery tests good.
-Car starts quickly in cold or hot. Just idles like crap and there is hesitation on the accelerator while idling in cold or hot. More hesitation when AC , lights, are on to where it almost drops to die/shut off, but never actually does.

On saturday, I had to get my car towed because I was afraid it was going to shut off after driving it a few blocks. With everything on AC, fans, etc, the voltage seemed to drop at idle and felt like the car was bogging down wanting to die.


So at this point I have no idea what is going on. What gets me is that this started from one day to the next, not a gradual decline of performance or symptoms.
Trying to reach out to see if anyone has experienced this.

The only other thing that comes to mind is the CPR/WUR. Mine was working just fine, then this started happening. It is about 14 years old though. I assume it is still good, but I have a spare one I was going to swap to see . But like I said the car seems to start fine when cold but has slight acceleration delay when idle and idle sounds chugg chugg . The last time I replaced the CPR/WUR was 14 yrs ago, and I remember it was more gradual symptoms of hesitation on cold start up than actually it being an over night thing.

Anyways, I'm stumped at this point. I hate to say it is spark plugs, or anything else ignition related because it just happened over night for no reason.

Really appreciate any info,

Thanks!!

[Bitsyncmaster]

What is your voltage at idle?

Does is sound like a miss fire? The two pin connector from the pickup coil can oxidize because some get wet. Unplug and plug that in again. Also can do the same with bulkhead connectors. A sudden change is probably electrical. While your at it unplug and plug the ignition resistors.

[Beachdrifter]

What is your voltage at idle?

Does is sound like a miss fire? The two pin connector from the pickup coil can oxidize because some get wet. Unplug and plug that in again. Also can do the same with bulkhead connectors. A sudden change is probably electrical. While your at it unplug and plug the ignition resistors.

Hi Dave

It still sounds like it's running on all cylinders, just sounds rougher and deeper rumble than normal.

I disconnected and sanded the contacts on the coil, disconnected the bulkhead connectors. All tight and started it again with the same.

Battery is reading 12.5v cold. With car on normal 14v range. Even with all accessories on. Although the dash voltage gauge reads like 12.9v with car on and all accessories. It never seems accurate unless that is an indication of an electrical issue beyond battery or alternator voltage. Did the same with the resistor connectors and nothing changed.

Thanks.

[painterdave72]

How old are the injectors?? everytime i have worked on a Delorean its usually fuel related issues that cause misfires...

[Bitsyncmaster]

I would check your primary and control pressure. I have seen PPR o-rings fail suddenly but that is usually results in hot start problems. Have also seen the WUR get a dirty screen but would not think that would be a sudden change. The heater in the WUR can fail suddenly but that would only affect your cold running engine.

[Beachdrifter]

How old are the injectors?? everytime i have worked on a Delorean its usually fuel related issues that cause misfires...

Thanks, the last time I replaced FIs were around 2013. So I would suspect they are OK. But anything is possible.

[Beachdrifter]

I would check your primary and control pressure. I have seen PPR o-rings fail suddenly but that is usually results in hot start problems. Have also seen the WUR get a dirty screen but would not think that would be a sudden change. The heater in the WUR can fail suddenly but that would only affect your cold running engine.

Thanks Dave, so I gave it a go and decided to just swap out the CPR/WUR with a brand new one I had laying around as a test bench. Unfortunately it did not change anything. Worst case I have to hook up some gauges and see what my fuel pressures are.

I did notice that I waited about 4 mins for the car to heat up, and my dwell was stuck at 20 (40 for 4 cyl) the whole time, and it wasn't until I throttled it a bit that then it began to cycle and "hunt" as it usually does. Prior to that it seemed it wasn't trying to "hunt" idle on its own. I found that strange. Definitely I feel something is wrong here, but the freq valve was buzzing and I just put on a fresh 02 sensor so it must be working also.

[David T]

It may not be fuel related. The problem sounds like it could be old/bad ignition wires. Moisture from parking outside could have triggered this.

[Bitsyncmaster]

I did notice that I waited about 4 mins for the car to heat up, and my dwell was stuck at 20 (40 for 4 cyl) the whole time, and it wasn't until I throttled it a bit that then it began to cycle and "hunt" as it usually does. Prior to that it seemed it wasn't trying to "hunt" idle on its own. I found that strange. Definitely I feel something is wrong here, but the freq valve was buzzing and I just put on a fresh 02 sensor so it must be working also.

That seems a little long for warming up. I think what triggers closed loop is the O2 sensor warming up enough to start producing voltage. So taking that long suggests the O2 is running cooler for some reason. Now I would verify your getting the two grounds at the lambda ECU. Those two grounds go to the bulkhead connector and then get grounded at the engine block.

[Jonathan]

Bad gas? When was the last time you filled-up? Maybe your local gas station gave you half a tank of water with your gas.