82 CIS idle dip

[tsuter]

He has a "dip" not a "hunt". Different problem..different solution. Try a search on "hunt" you'll get about a 1000 threads. Focus on CIS cold start hunt.

[braddb_82SC]

Originally posted by Barclay
I to am having similar problems with my 1981SC coupe, cold start rpm hunts up and down for idel breifly and then goes away then at operating temp it will start hunting for idel again when you push in the clutch. ( it almost dies) I don't think it's a vaccum leak because when I take off oil cap the idel changes noticeably I am going to adjust mixture 1/4 turn counter clockwise to see if that will help, what else do you guys think?

I'd adjust in 1/8 turn increments. After each adjustment, drive the car around a bit. Maybe a couple days. Then adjust again if you need to.
1/4 turn will change your %CO several percent. This is too much when you are fine tuning without a Gunsen Gastester.

-Brad

[braddb_82SC]

Originally posted by tsuter
He has a "dip" not a "hunt". Different problem..different solution. Try a search on "hunt" you'll get about a 1000 threads. Focus on CIS cold start hunt.

Yes but both seam to be correlated to a rich mixture. After adjusting my mixture from 0.7 to 3.5 %CO I started having a cold start hunt and an idle dip. The hunt goes away after a few miles. The dip does not. I'm not too concerned about the cold start hunt presently. It's not as bad as on several '80's BMW's I've owned or driven.

-Brad

[ohecht]

tsuter,

By "masking", I meant that the higher idle is sort of making the dip much less noticeable since it does not dip as low in total, but I can still tell it is not a smooth movement to idle without overshooting.

Olivier

[tsuter]

Originally posted by braddb_82SC
After adjusting my mixture from 0.7 to 3.5 %CO I started having a cold start hunt and an idle dip. -Brad

Jeez - who told you to do that?? On an 82??

edit: or have you removed your cat, air pump, o sensor etc>???

[tsuter]

Originally posted by ohecht
By "masking", I meant that the higher idle is sort of making the dip much less noticeable since it does not dip as low in total, but I can still tell it is not a smooth movement to idle without overshooting.

Olivier

You're right about that it will be MUCH less noticeable....

I hate to assume things but if you're not experiencing sensor plate overswing due to a bad leaf spring or incorrect adjustment and your CO is set where you want it......per spec....

Then raise that idle another 25RPM until the dip goes away.

If you want to see it dip and die on each shift just lower it to 750-800. You'll soon find the right spot.

This ain't rocket science.

[Paulporsche]

Try it. It always works for me.

I get a rock steady idle, plenty of pep with no "choked off" feeling, no idle hunting or dipping, no pinging, and a very dark brown (not black) tailpipe.

With the idle slightly raised, then I am OK for that muggy, rainy day when the air, wipers and headlights are all on.

If you encounter pop valve popping (late fall for me) then richen it back up.

I don't have a clue what my CO is. I just know this has worked for me for the last 15 years.

Good luck.

Paul

[braddb_82SC]

Originally posted by tsuter
Jeez - who told you to do that?? On an 82??

edit: or have you removed your cat, air pump, o sensor etc>???

No air pump on an '82.

Yes, per JW's recommendations I have removed the O2 sensor, and replaced the cat with a test pipe. JW recommends 3.5% CO + 30-35% total timing advance.
I also did some CIS refurbishment. Last time I had the engine out I replaced all gaskets and seals on the CIS to eliminate vacuum leaks. I also replaced all fuel injectors. I don't believe you can properly tune your car until you have confidence in the fuel and ignition systems.

-Brad

[tsuter]

Originally posted by braddb_82SC
Yes, per JW's recommendations I have removed the O2 sensor, and replaced the cat with a test pipe. JW recommends 3.5% CO + 30-35% total timing advance....

......recently used my Gunsen to adjust my mixture from 0.7 to 3.5 %CO. I immediately started having the same problem you are describing. Idle drops to 400 RPM on deceleration..
-Brad

That is way tooo funnny!!

Maybe then he'll tell you how to get rid of your "cold start hunting" and "dips" then. LOL