SC Super low idle...only for a minute.

[jchris]

So I got under the car today, adjusted the clutch and checked the throttle linkage for full range ( with the wife's help! ). No adjustment was made to the throttle linkage other than to tighten up a loose locknut. I got the car care off the jackstands and went to test drive it. When I started it it caught right away and then idled really low, less than 500RPM then stalled. I tried a second time, it caught right away then went to this ridiculously low idle but stayed there this time. I tried the accelerator but no response. I thought that the linkage came off , but no.

Frustrated, I went inside for a minute, came back out and inspected for something I may have disconnected accidentally. Nothing. I reverified that the bell crank was operating the butterfly, and tried again. This time it started and idled perfectly!

Here are some facts. Car has been operating really well and is again. Warm and cold pressures are correct. Idle has been set with sears analyzer as per the advise found on this forum. This was all recently when I installed my new exhaust. Occam would have me believe this had something to do with what I did today, though I can't imagine how. Otherwise the only thing I can come up with is that the O2 relay took a five minute break, and is now cooperative again.

Any thoughts?

Thanks!

[Guvnor]

I have this same cold start issue, though mine has never stalled and the low idle is only for a few seconds before the enrichment circuit kicks in creating the higher idle until warm. For me, it all started after I replaced stock muffler and CAT with an M&K one-in-out muffler and their pre-muffler system (cat-delete). If the motor is warm or even slightly warm everything is fine. Additionally I did notice that on cold starts with the O2 sensor disconnected start-up is normal.

Sub'd in hopes that you find the issue.

[Bob Kontak]

Try plugging your retard hose to the distributor vacuum unit. Stick a nail in the hose.

It's the hose that sucks at idle. The advance hose does not suck until you gain RPM.

Gives you several degrees advance at idle to help with start up.

I used to have the 500 RPM chug at cold start then RPMs would kick in but not really go up to the nice healthy 1500-1700 RPMS unless is was as cold as a well digger's butt.

Not sure if this was the sole reason, but I know it helps band-aid a few age issues with CIS components.

It also band-aids issues you can correct yourself so kill the vacuum leaks, etc, etc.

Hope it helps. psalt turned me on to this easy enhancement.

I was/am running a cat bypass but I remember this happening before I changed out the cat.

[john walker's workshop]

might be the domelight fuse. it powers the OXY sensor computer/frequency valve relay. or the relay itself. it's under the right seat by the tunnel. warm up the car and unplug it. idle will drop way off if the system works. or pull the domelight fuse, same thing.

[jchris]

Thanks! I already disconnected and pluged the vacuum retard at the advise of this board( probably you and psalt! ). It did solve my wondering idle. I will look at the fuse and relay contacts to look for corrosion. I remember reading that some have replaced the o2 relay and had positive improvement, even though the old one was functional. Was that either of you?

Thanks again.

[Bob Kontak]

Originally Posted by jchris

I remember reading that some have replaced the o2 relay and had positive improvement, even though the old one was functional. Was that either of you?

It was another guy but I followed his lead and noticed a difference in crispness. I do remember posting about this. Kind of felt like a tune-up but it would not fix your bog at start-up - assuming the relay is functioning at all times.

Given you have plugged the retard hose. Listen to John and start your car with the OXY fuse disconnected. If it is identical as to cold start idle when not running properly/bogging, you have a good starting point.

[fireant911]

I can vouch for what Bob Kontak is saying regarding the 'crispness'. I was quite taken aback by the improvement I experienced by just replacing an 'either on or off relay'.

81 SC Oxygen Sensor Relay

[Bob Kontak]

Originally Posted by fireant911

I can vouch for what Bob Kontak is saying regarding the 'crispness'. I was quite taken aback by the improvement I experienced by just replacing an 'either on or off relay'.

Maybe it's a simple as the contacts get a wee bit corroded and the juice level is compromised? I don't know.

But it was a step-change improvement from the old one.

[jchris]

Well I checked the contacts on the fuse and relay and nothing obvious there. I will try starting it with the fuse out for fun and see if that replicates it. I may try throwing in my spare relay as well. +1 on the on or off comment. I feel like it should work......or not. But I will try for fun. I will post what I find!

Thanks

[jchris]

Finally tied this one up. No one here will be suprized that when I pulled the dome light fuse it replicated the issue. Must be slightly corroded. Maybe a little light bulb grease will do it.


Thanks all, and sorry for the late closure of the thread!

[Bob Kontak]

Originally Posted by jchris

Finally tied this one up. No one here will be suprized that when I pulled the dome light fuse it replicated the issue. Must be slightly corroded. Maybe a little light bulb grease will do it.


Thanks all, and sorry for the late closure of the thread!

Sweet - Hey, thanks for closing it out. Great job.

I have read where peeps will cut off a #2 pencil with an eraser on it and put it in a drill and "erase" the crud on the fuse contacts vs using something more abrasive.

Hint: Make a note to yourself - when John Walker suggests something, look into it.

Just for clarification - when you used your Sears analyzer, you adjusted the AF mixture. Not the idle. The idle air bypass the big screw that simply lets more or less air bypass the closed throttle does not change the AF mix.

Here is something to put in your hip pocket. If your system has ZERO vacuum leaks there are four conduits that allow air to bypass the closed throttle. The two space ship things on the passenger side of the engine buried in all the CIS plumbing (decel and Aux air valve), The auxiliary air regulator bolted on near #5 intake runner and the big fat air bypass screw on the driver's side of the throttle body.

Study this for fun:

911 CIS Primer - Components

[jchris]

Thanks Bob, I probably miss spoke some where but I do (after some monkeying about) end up adjusting both the air screw and the idle mix together as they affect each other. Last time I set it closer to 40 on the anylizer, leaving it a smidge (scosh?) rich. It seems to like it. Any way I will try the eraser on the fuse ends. This machine was left in a damp garage for about ten years before I found it. Many things have needed or still do need attention.


Anywas thanks again, I appreciate all the advise!