Engine Hunts at Start and Then Rough Idle When Warm

[Jonathan]

Lean it out a bit and see if it changes.

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?

Also, "a little bit" is not very much. I recall when I was looking over my mechanic's shoulder while we were adjusting things, the full range from a lean stall to a rich stall was a half turn. Meaning, if you put your screw driver in that hole and it is lining up with say the 12 o'clock on a clock face, you are only going to want to go a few MINUTES of equivalent turn as the entire span would only be about from the 9 o'clock position to the 3 o'clock position. Less is more with these adjustments. Make a tiny change, then give it a chance to make an impact. Then make another small change. And don't forget where your starting reference point was.

[Morpheus]

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?

CCW = lean, CW = enrich

"A little bit" is a relative turn, but I would say if you are using a long "T" handle allen wrench, you would equate it to a 1/16th of a turn or less. A minuscule adjustment makes a big difference when dialing in the CO.

[Bitsyncmaster]

And for the sake of clarity, the lean direction for that adjustment screw is clockwise or counterclockwise?

Also, "a little bit" is not very much. I recall when I was looking over my mechanic's shoulder while we were adjusting things, the full range from a lean stall to a rich stall was a half turn. Meaning, if you put your screw driver in that hole and it is lining up with say the 12 o'clock on a clock face, you are only going to want to go a few MINUTES of equivalent turn as the entire span would only be about from the 9 o'clock position to the 3 o'clock position. Less is more with these adjustments. Make a tiny change, then give it a chance to make an impact. Then make another small change. And don't forget where your starting reference point was.

It's more like a 1/4 turn to go from one extreme dwell reading (10 deg) to the other (85 deg.). I have not test it to engine stall.

[lazabby]

Here is an update and mostly the news is good. Per the suggestion in the thread, I unplugged my CO2 sensor. The car was running and up to operating temperature with fans cycling. I plugged in the dwell meter. As before, the reading was between 10.5 and 11. I then unplugged the CO2 sensor and the dwell meter reading went up to about 44.7 with little variation. Here is the video of that:
https://youtu.be/clMgiVDDjhQ
Whatever adjustment I did on the idle mixture screw did not budge the reading.

I then plugged the CO2 sensor back in and the dwell meter began fluctuating as it should. I then worked on the tune and here is what I believe is the last video I took:
https://youtu.be/CMB0WZUy0ao

The engine actually ran a little bit smoother a couple of days ago when I was unable to get a good reading. If you listen carefully to the video the engine isn't quite smooth but it runs well enough now to drive around. This morning I started the car with a cold engine and it fired up almost immediately. The idle wasn't fluctuating but I would like to smooth it out a little more. I'm not sure if I need to barely tweak the mixture screw or if it's something else.

Bottom line is that I have a driveable car. I''l probably get a few miles on it and put the meter on it again and make a very slight adjustment.

Any other tips?

[Bitsyncmaster]

You will get a smoother idle running the mixture rich. But then you get bad MPG, smelly exhaust, damaged CAT. Is that smooth idle really that important?

[lazabby]

I took it out for a longer drive yesterday. It hunted a bit when first started. I turned on the AC after a few minutes after it was warm and noticed that the RPM was surging erratically. What's going on? Turned off, the idle was fairly stable.

[lazabby]

I'm still having an issue where my car hunts when cold. I can drive the car around and get it warm and put a dwell meter on it but the dwell meter is not getting a good reading whether in the "unused" plug or at the bulkhead. Instead of fluctuating it hangs about 54.8 (at 4 cylinders). I can't understand why it's doing that. the CO2 is new. The car runs fine when warm. I really want to get rid of the hunting when cold.

[Elvis]

Read the manual, there is no closed loop control when cold.


repetition: PID controller can't handle dead times. cold engine - richt mixture - slow reaction - dead time !


10 years ago I suggested to modify the idle ECU to improve the reaction time, but I was called stupid
for doing that...delorean has to hunt...

[Bitsyncmaster]

I'm still having an issue where my car hunts when cold. I can drive the car around and get it warm and put a dwell meter on it but the dwell meter is not getting a good reading whether in the "unused" plug or at the bulkhead. Instead of fluctuating it hangs about 54.8 (at 4 cylinders). I can't understand why it's doing that. the CO2 is new. The car runs fine when warm. I really want to get rid of the hunting when cold.

Your wide open throttle switch is stuck on or less likely your "idle speed regulator switch" is shorted. Just pull one wire off the wide open throttle switch.

[David T]

There is no getting around the PRV hunting when cold. You can reduce it but not eliminate it. To reduce it to a minimum you must get each cylinder set up as close to each other as possible in terms of adjustments. That means checking (and if necessary adjusting) the valve clearances, spark plug etc. The cylinder pressures must be within 5% of each other too. Even in closed loop it will "hunt" a little as the frequency valve modulates.