Sudden rough idle & Hesitations after parked overnight!

[David T]

If you are going to try injector cleaner the one I recommend is Techron. Follow the directions. I doubt it will fix the problem but it can't hurt. The only way to fix a problem like this is to diagnose and troubleshoot in an orderly and logical sequence. Otherwise you wind up just throwing parts at it till you get lucky. You can fix things that way but it can get very expensive (and you waste a lot of good parts).

[louielouie2000]

My car is actually doing something very similar right now; it’s stumbling and tries to die while driving until it gets up to operating temperature. My entire fuel system was replaced about a year ago so I’m pretty baffled too. When I called DMCH they suggested I check the electrical connectors on the bulkhead and look for vacuum leaks. I ended up trimming up some of the vacuum hoses but still need to try hitting the vacuum components with carb cleaner while the car is running to see if there are leaks elsewhere. They suggested I do a CO adjustment after I check for electrical connections and vacuum leaks; my car is absolutely running way too rich. Sounds like any number of things can throw off your fuel mixture and cause these rough running issues. Good luck with your car and let us know what happens with it.

[Beachdrifter]

Thanks everyone for your insights.

I'm still troubleshooting this issue, although I haven't had much time during the work week.

I did throw in some techron, figured that couldn't hurt.

I also checked grounds again on the Lambda, and as many vacuum connections, they seem to check out for now. I understand a good smoke test will eventually come in handy, but I figured since this started overnight, maybe my vacuum hoses are fine.

What came to mind is disconnecting the thermo time switch to the cold start valve. I went ahead and disconnected that to see if my car would start. It started right up as it usually does. Which makes me wonder, is it possible that my CSV is stuck open or leaking fuel all the time, partially open perhaps, causing my new condition of rough idle, and rough engine running? Too much fuel getting in there making everything go haywire?

I could feel the car instantly run a little better when i first turned it on with the thermo switch disconnected -- car had been sitting for over 24 hrs prior.
Maybe I need to look into the CSV, pull it and see if it operates as intended, or get a test bench unit to test on.

Any thoughts on this?

Thanks,

[louielouie2000]

I’m pretty sure my issue is too much fuel, too. The engine seems like it’s drowning in fuel until it gets up to operating temperature and then it’s fine. I replaced the warm up regulator and nothing really changed. I didn’t realize cold start valves had gotten so rare & expensive; yikes.

[Bitsyncmaster]

What came to mind is disconnecting the thermo time switch to the cold start valve. I went ahead and disconnected that to see if my car would start. It started right up as it usually does. Which makes me wonder, is it possible that my CSV is stuck open or leaking fuel all the time, partially open perhaps, causing my new condition of rough idle, and rough engine running? Too much fuel getting in there making everything go haywire?

I could feel the car instantly run a little better when i first turned it on with the thermo switch disconnected -- car had been sitting for over 24 hrs prior.
Maybe I need to look into the CSV, pull it and see if it operates as intended, or get a test bench unit to test on.

Any thoughts on this?

Thanks,

The CSV only gets power when the starter is cranking. So pulling the TTS would only affect starting. I have found my car starts better in warm weather with the TTS disconnected. Now the CSV may have a mechanical defect in that it is not turning fuel flow completely off. You could test that putting the CSV in a jar with the engine running (you would need to plug the pipe where it was removed).

[Beachdrifter]

The CSV only gets power when the starter is cranking. So pulling the TTS would only affect starting. I have found my car starts better in warm weather with the TTS disconnected. Now the CSV may have a mechanical defect in that it is not turning fuel flow completely off. You could test that putting the CSV in a jar with the engine running (you would need to plug the pipe where it was removed).

Good info Dave, thanks.

Well I pulled the CSV and tested it with it disconnected and connected with car on. Both the valve and switch are working as intended, it squirted out fuel just on crank and is not leaking.


So onto the next theory... when I get one... lol.

I still can't believe this happened overnight. Perfectly running car one day, next day runs like it never ran good before.

The only thing I have pending is waiting for a nos vacuum solenoid I ordered since mine i know is bad. Other than that, perform a vacuum leak test, but still even that I don't understand how that could happen from one day to next.

Well to be continued.....where we're going we don't need roads, just jack stands and a garage!!

Lol..

[AugustneverEnds]

I'm sorry your issue is proving so elusive.

The more I read about your symptoms and what you have already verified the more strongly I feel you are having the same problem I did in 2019, a bad ignition cap and/or ignition distributor. My cap had barely visible cracks and when it was damp out (frequently in the humid summers in NY) the car would start fine but run erratically. Some of the problems were resolved when I replaced the cap but upon further inspection the dust cap/moisture shield in the distributor itself was cracked and moisture had become trapped in the body of the distributor. I had the distributor rebuilt in 2020 and the shop that did it found a considerable amount of corrosion especially on the impulse coil. After the rebuild all the issues were gone.

[Beachdrifter]

I'm sorry your issue is proving so elusive.

The more I read about your symptoms and what you have already verified the more strongly I feel you are having the same problem I did in 2019, a bad ignition cap and/or ignition distributor. My cap had barely visible cracks and when it was damp out (frequently in the humid summers in NY) the car would start fine but run erratically. Some of the problems were resolved when I replaced the cap but upon further inspection the dust cap/moisture shield in the distributor itself was cracked and moisture had become trapped in the body of the distributor. I had the distributor rebuilt in 2020 and the shop that did it found a considerable amount of corrosion especially on the impulse coil. After the rebuild all the issues were gone.

Thanks Nick, I'm starting to think this is leaning to a more difficult fix than what's on the surface. What you're describing makes sense . I can tell you mine is at least 17 yrs old. My car always stayed garage and rarely stayed parked outside over night. The day I drove it , it was fine. Then left it parked outside overnight, and next morning started with the rough idles and engine shaking all over the place, weak acceleration response.

Perhaps some morning dew, moisture made some things haywire back there. I've never done that job before and would mean the dive into the valley of death. That dreaded moment maybe it has to come to that.
I also want to say that in almost 20 yrs I've only driven the car like 10k miles, so maybe corrosion has built up in the cap that hasn't really had time to burn off or wear out.

Well, I will keep everyone posted, I will not end this thread until the solution is found.


Thanks,

[Beachdrifter]

Ok my friends,

Replaced vacuum solenoid with a perfectly operating one and no change.

After running out of options I decided to focus on the ignition system now. Early on in my diagnosis I replaced spark plugs, figured that was easy enough.
However that didn't change the rough idle condition or slow throttle response. I then started to get a popping sound in my exhaust, even though new plugs were gapped properly. This made me suspect my ignition was running weak and not burning up the fuel causing an enriched backfire in exhaust. But I didn't want to believe a weak ignition system just like that.


But now, I went ahead and bought an ignition spark tester and also one that is inline with a bulb.

I decided to perform this test as seen in the short video below:

https://youtu.be/IbzhxgD3ZUI

I did just the 3 plugs on the passenger side as a trial.

Per the video, any strong ignition system should pull "30" with a consistent spark. Well, mine didn't even spark at 30, and didn't start sparking until I reached 20.

I then hooked up the inline tester with a bulb, and the bulb flashed erratically, that per the product's packaging, "erratic bulb flashing is an indication of weak ignition system or fouled plugs".

Well, so previously I did a test and swapped my coil, it caused no difference so my current coil must be good.

Plugs are new.

That leaves based on the indications above that my ignition distributor system is failing in some way that is causing weak spark? Is the "30" expected for older based ignition systems like ours or more for electronic ignition? Not sure what the baseline for a normal running Delorean is.

Thanks!

[Beachdrifter]

Let me add, that the inline bulb test was blinking... maybe not really and indication that something was wrong since just consistent blinking is normal as I saw other videos.

I'm mainly interested if our ignition systems should be putting out a consistent 30kv or are the rated for 20kv?

Thanks