Cold idling problem just after first start in the morning.

[outatym2001]

I’ve got a cold idling problem that has crept up recently. There is no problem with idling when the engine is warm.

At first start in the morning when the engine is cold it starts normally and idles normally for six seconds then drops to 500-600 rpm then speeds up to 1,000 rpm then after six seconds it drops to 600 rpm then to 1,000 then slowly drops back down 500-600 then up again around 1,000. If I don’t touch anything after 25 seconds it will slow down to 500 rpm and then die.
After it dies I can hear the Frequency Valve (102395) buzzing like a mad hornet on the passenger side valve cover and it stops after two seconds.
When I immediately start it up again it does the same thing all over and dies after about 25 seconds.

I can depress the gas pedal to prevent it dieing but I need to hold the pedal for about a minute then it’s warmed up enough so that it doesn’t slow down and die on its own.

Things I’ve done to try and fix the problem. I lifted the inlet manifold and replaced the Constant Idle Switch, Thermister (102480). That didn’t fix the problem.

Then I removed the Idle/Low Speed Motor (102502) and cleaned the air passageway with brake clean and paper towels until it was clean and the mechanism inside rotates smoothly then I reinstalled it and I still have the cold idle problem.

Then I removed the Warm Up Regulator (102353) and disconnected the two fuel lines and removed the bottom cover plate and the insides look perfectly normal and no burned wires. I made sure the filter screen is clear of any debris. After reinstalling that didn’t fix the problem either.

I am at a loss of what to do next?

[Bitsyncmaster]

Not uncommon to get "hunting" idle with the cold start. The lambda ECU is holding the FV at a fixed dwell until the O2 sensor has warmed up. Small differences in each engine can make some not hunt and others hunt. Most critical is the idle motor not sticky when it's moving. Make sure your mixture setting is correct with a dwell meter after the engine has warmed up. You can also adjust your curb idle screw and find a "sweet spot" where it might stop the problem.

[David T]

Sounds to me like the Control Pressure Regulator is acting up. Can be verified with a fuel system pressure gauge and watching the fuel pressures as the motor warms up. Also check the vacuum advance.
David Teitelbaum

[82DMC12]

I recently went through some hot idle problems that took forever to figure out until I checked my timing and found I had an advanced condition at idle. If you have a timing light, you might want to do that. You probably wouldn't have the same problem I did since yours is at low temps, but it wouldn't hurt to check it anyway. The timing should NEVER be advanced at idle.

Andy

[outatym2001]

John the mechanic at DMC Northwest first checked my DeLorean for anything out of place or possibly any vacuum leaks and he found the black plug (plug to vacuum solenoid) was disconnected. Vacuum Solenoid is part number 101116 item 27 on page 2/4/0 of the Parts Manual. For the life of me I don’t know how it came unplugged. Maybe when I was replacing the Thermister under the intake manifold and I disconnected it somehow.
Next he hooked up the dwell meter inline with the Frequency Valve and it clearly showed the duty cycle was running a rich mixture cycle.
He adjusted the idle adjusting mixture screw at least half a turn and the cycle is now within the proper range. How the mixture screw rotated on its own I don’t know. This problem took a while to show itself. All is better now and now I can go back to drag racing those moms in their minivans.

[Bitsyncmaster]

Glad your fixed now. Mixture could change if your WUR control pressure changed or the O2 sensor changed. Both of those compo nets seem pretty stable with age. Was it ever adjusted correctly before?

[outatym2001]

Glad your fixed now. Mixture could change if your WUR control pressure changed or the O2 sensor changed. Both of those compo nets seem pretty stable with age. Was it ever adjusted correctly before?

Bitsynmaster glad you mentioned the O2 sensor since it reminded me to look at my old receipts and the last O2 sensor I bought was July, 2006 from http://www.specialtauto.com
I reset the Lambda counter under the dash at that time and I did not record what the mileage was. I was also driving with a broken Right Hand Angle Drive so the speedo/odometer didn’t work.

Looking at my old receipts I can’t find when I had DMC Northwest check for proper air/fuel mixture. I'm positive they checked it for me since just a few years ago when the engine was running rich it ended up melting some of the internals of the catalytic converter.
So I removed the cat then busted out the insides with a two foot long crow bar then reinstalled the hollowed out cat.

[Bitsyncmaster]

So I removed the cat then busted out the insides with a two foot long crow bar then reinstalled the hollowed out cat.

I have done the same.

[sdg3205]

Then I removed the Warm Up Regulator (102353) and disconnected the two fuel lines and removed the bottom cover plate and the insides look perfectly normal and no burned wires. I made sure the filter screen is clear of any debris. After reinstalling that didn’t fix the problem either.

I am at a loss of what to do next?

Is there a torque spec for reattaching the fuel lines? same as the top of the distributor?

[Ozzie]

Is there a torque spec for reattaching the fuel lines? same as the top of the distributor?

Here ya go.
http://dmctalk.org/attachment.php?attachmentid=1181&d=1308271170
Not mine, from the old archives.

[sdg3205]

That's great, thanks Ozzie!