Rough, Stumbling Idle Until Warm

[OK-944]

Just started last week, turned over the key and the car’s engine caught and then died.

What works is to keep feathering the gas for about a minute (during which time it feels like a cylinder is missing), after which it proceeds to idle low and roughly (cylinder missing occasionally) for about another minute. After this, it takes a good five minutes of driving (allowing running temperature to settle) before all feels well, except for a very slight lower idling RPM…around 800 vs the usual 900, then closer to 900 after about half hour of driving.

Other than the above, the oil pressure comes right up as per usual, and on a 120 mile drive yesterday my car generally felt great (nothing weird coming out the tailpipe, no strange noises) and achieved 28 MPG. Voltage indicated as steady at around 13.8 to 14 while driving

Note: I’d recently completely rebuilt the engine, during which I also cleaned up and coated all ground connections. Also replaced both engine sensors and O2 sensor, plus installed a new fuel pump and filter.

Aside from the usual suspects, like checking sparkplug, coil, and injector connections, and maybe popping off the distributor housing the check/clean those contacts (don’t think its the ICV as things settle down when warm) - is there anything else I could check at this point? Thanks!

[wwdwgs]

Do you think this problem is temperature dependent?
Could it be a coolant temperature sender to DME?
Is there any useful information on Clark Garage site to troubleshoot "your" condition?

[Jfrahm]

Get it to run badly for a bit, then shut it off and check the plugs. Are they wet? Black?
Sounds like it's rich until it gets into closed-loop, which might mean extra fuel. Probably one of the usual reasons.

-Joel.

[OK-944]

Switched out DME relay and all is well...but I don't think that was the issue.

It was also close to 70F today, and closer to 40F when starting was rough. So I do think this is temperature related.

During my rebuild, I did replace both the head and radiator temp. sensors.

I'll need to live with this for a couple of weeks before I have time to dig further...and in the meantime, hopefully the weather will continue to warm as the season progresses.

In the meantime...thanks for the suggestions!

[Jfrahm]

Hard to believe you were running a dodgy DME relay before.

[Monkey Wrench]

just a hunch , but if you have n injector stuck open or partly open, that can drain your pressure in the fuel rail into one piston hole.. next, when you start it will probably put out some white smoke and may run on 3 cylinders with one wet plug. it'll basically run crappy and lack power.

The condition can clear itself, since the injector works normally other than being leaky and any extra fuel will be expelled ,

If you try what Joel suggested ( check when it runs crappy) you may note if one plug looks different from the rest. or possibly one stinks of raw fuel. If you inspect plugs after some normal running, they may look fine again..


if it were a slow leakdown , that might lead one to think its temp related , as without time between not much fuel leaks , so it starts normal when warm. A stuck open injector may take time to leak enough fuel , to present a problem,

you can do a leakdown test or check the injectors out of the car or crank it a bit to watch the spray and shutoff, (be careful of causing a fuel fire) you could swap the injectors around to see if the problem follows the injector.

next tine you start it, see if you can observe any white smoke in your rear view mirror when you give it some pedal.. I had that happen in my volvo and after about 3 blocks and a bit of throttle it would "fix itself" till the next morning.

Just a theory, this isn't conclusive..

[walfreyydo]

"Blue top" DME temp sensor (different from the coolant temp sensor and the radiator thermo temp switch) and IACV are two common culprits as outlined on good ole clarks
https://www.clarks-garage.com/shop-manual/ts-01.htm

[Rpaillet]

Did you find the problem?

[originalowner]

Possible vacuum leak.

Lower temp requiring richer mixture to run. Opening throttle results in a higher percentage of air being metered, thus richer mixture (but still lean.)