Lean Or Rich?

[Koizumi]

My 84 is slow to drop rpms when I put it into neutral or downshift. Takes 2-3 seconds before the rpms drop normally.

I messed with the AFR a while back but I can’t recall if I leaned or riched it.

Is 2-3 seconds hanging idle while neutral/downshift lean or rich?

I did finally cure the idle as it was hanging at 2k.

No vacuum leaks, rebuilt engine and resealed 400 miles ago. I just can’t seem to dial in the throttle and AFR. Of course I don’t have an air meter but perhaps one of you can elucidate on if this situation is due to lean or rich.

New O2 sensor, new plugs, distributor, rotor, cap, fuel filter, etc. Doesn’t leak a drop of oil (for now lol), Steve Wong chipped... New throttle body, throttle switch clicks ok... Dreaded cruise control is ok and ziptied like a champ.

I’m confused. The hanging 2-3 second idle is terrible.

[Uwon]

Maybe too much air. Idle control motor stuck fully open? Put your hand on it and have somebody turn the ignition on. Does it click then hum?
Johan

[stlrj]

"throttle switch clicks ok"

But it still may be out of adjustment.

[T77911S]

rich or lean wont make the idle hang like that.

I would disconnect the ICV and see if it still does it.

[Koizumi]

It’s a new ICV. Both my old one and the new one click ok with a 9v battery.

When the car is off, the throttle cable clicks. Does the switch assembly adjustment (gently hammering it back or forth) make a difference even if I can hear and feel a click when the throttle is seated? Is it a super finesse micro adjustment process despite hearing the click?

[stlrj]

But if the DME isn't getting the message from the throttle switch that it's closed, your idle will hang up. Don't blame the ICV.

[T77911S]

that's my point ^^^^^

[Koizumi]

I did disconnect the ICV, and I tried 2 different units that are battery tested and working.

Linkage under the car appears good as well.

How little does one move the switch? I moved it despite it clicking (still clicks). Is this thing ultra sensitive to micro adjustments despite clicking upon release of the throttle?

DME appears to get the message from the microswitch since the idle does settle after a 1-2 second hang in neutral/downshift. Looks like it’s fiddle more the switch adjustments?

[T77911S]

check the switch with a MM

[jpnovak]

Assuming the idle switch and ICV check out...

Also consider that the AFM barn door may be sticking and that the AFM internal resistor board may be worn requiring the re-positioning of the wiper arm. I have seen this a few times with cars that have a lot of stop/go idle time and in different spots from highway time.

[GH85Carrera]

Does your car still have AC?

On my 85 I have excellent Air Conditioning. When I go to autocross, I want the evaporator to blow air on me, but I don't want the compressor to run. The fresh air system is almost useless.

I just disconnect the compressor wire. The car still thinks the AC is on, and the evaporator motor is blowing but the compressor is not going to run with no electricity. The car will be slow to return to idle when the compressor is disconnected. As soon as I reconnect it, it goes to idle like normal. If the AC is off, it idles as normal.

I do have a Steve Wong chip. I don't know if the DME monitors the AC or not, but my car sure acts like it does. And it happens at all the summer time autocrosses.

[FrankM_]

Originally Posted by GH85Carrera

I do have a Steve Wong chip. I don't know if the DME monitors the AC or not, but my car sure acts like it does. And it happens at all the summer time autocrosses.

Yep, the power of the a/c is also routed to an input pin of the motronic dme so it can take that load into consideration

[GH85Carrera]

Originally Posted by FrankM_

Yep, the power of the a/c is also routed to an input pin of the motronic dme so it can take that load into consideration

OK, I figured it did. I seem to remember hearing Steve mentioning it.

[cabmandone]

Check your throttle linkage as well as your pedal cluster.

[Koizumi]

Hi all,

We all enjoy threads that not only pose questions, but we truly enjoy when the OP shares end results...

So, I tested continuity for the Idle Position Switch (terminals 42, 44) and it has continuity until 1mm gap. So, it’s good.

Next, continuity for Full Throttle Switch (terminals 3, 18). No continuity until full
open throttle. Good!

I then loosened up the microswitch and redid continuity until beep - then tightened up both microswitch screws. Check!

So the throttle microswitch is in working order and seemingly positioned correctly.

ICV checked again. Removed, 9v battery, clicks. Reinstalled, car on, hums like a champ. Good!

Redid the zip ties on the cruise control. Went overboard but what the hell, why not. Check!

Kinda snapped a part off of the cruise control servo vacuum line, approx. 8” of crumbly hose. Oh well, no big deal but my OCD made me buy a new hose even though the shortened old hose obviously works just fine. I assume that the end of this hose just pulls vacuum from the engine bay or poked thru the bay to the underside somewhere.

Shortened the pedal bar ever so slightly. Good!

Once again went under the car and really tried to nail 1-2mm floppiness for the throttle linkage to reversing lever gap. I mean I really really tried to get it just right.

So after all of this, I started up the car and drove it. No more 1-2 sec hanging idle! Drops instantly upon popping out of gear/downshift. And yea Steve Wong is right, there’s definitely more HP with the correct slack on the throttle rod system.

Now I’ve adjusted the throttle rod system many times over the years, this is a big reason as so why this was all such a head scratcher for me. Anyhow, I got lucky with the perfect 1mm-2mm slop on the reversing lever.

Now I’ve noticed the rpms drop close to stall. I must be running lean and/or gotta up the idle slightly. Anyhow problem solved...

Thank you all for your advice, input, etc.

Cheers

[cabmandone]

Are the RPM's staying low? If so you need to start looking for vacuum leaks. I wouldn't mess with the idle speed until you're sure there are no vacuum leaks.

[Koizumi]

No vacuum leaks. I pulled the engine a couple of months ago... Car nicely drops RPMs when I open up the oil cap.

My RPMs drop a little lower than normal upon downshift/neutral. Not enough to stall but still a tad too low. I played around so much with the CO mixture that I cannot recall if I’m lean or rich. I’ve had this issue years ago and I recall that a slight adjustment in the mixture and a tiny increase in idle solved it.

Would a lower drop in rpm and rebound upon downshift/neutral be due to being a little lean? If so I’ll turn the AFM counter clockwise a quarter or half turn to enrichen.

[stlrj]

Mixture is an unusual way to deal with rpm issues but using the idle air bypass adjustment screw is the logical approach the factory uses.

[Koizumi]

Originally Posted by stlrj

Mixture is an unusual way to deal with rpm issues but using the idle air bypass adjustment screw is the logical approach the factory uses.

Indeed. And make sense of course. I’ll do the idle adjust once at temp with B and C