Weird low idle issue..., Even weirder fix. Options

[speed metal army]

After an hour or so drive,the car want to idle super low,and stall.I can keep it from happening by blipping the throttle.I let it die in the driveway,unplugged a vac hose from the decel valve,and fired it up.Of course it fired up and idled at about 1500 rpm or so.I plugged the hoses back in to the decel,and it idles fine,bout 950 rpm.
So what the hell is going on? (IMG:style_emoticons/default/biggrin.gif) By creating a vaccuum leak,then stopping the leak,it gets my idle back to where it should be,like magic.Ive checked out Brads site,searched etc..CHT sensor?Doesnt seem like it would be...Im not changing any thing except creating a short temporary vac leak,then stopping it.
The car bucks a teeny bit,but ive attributed that to the TPS(I think!)
Could a bad TPS be creating a crappy idle at temp?


Weird. (IMG:style_emoticons/default/confused24.gif)

Its a 76 w. Stock FI.Also the car actually fires up and idles nicely when cold.

[SLITS]

Other than being to rich @ idle when warm ....

1.) Points are closing up

2.) Idle mixture set to rich on knob on ECU. Start point is middle of range.

3.) CHT is out of specification when warm

4.) Temp Sensor II has taken a crap ... senses incoming air temp.

Adding air via vacuum leak is leaning the mixture.

Hell, you know the drill .............

[speed metal army]

Other than being to rich @ idle when warm ....

1.) Points are closing up

2.) Idle mixture set to rich on knob on ECU. Start point is middle of range.

3.) CHT is out of specification when warm

4.) Temp Sensor II has taken a crap ... senses incoming air temp.

Adding air via vacuum leak is leaning the mixture.

Hell, you know the drill .............

Temp sensor II?Where the heck is that?

I know im leaning the mix when I create the leak,But why the heck does it Idle fine as soon as I eliminate the leak?

[SLITS]

Wild ass guess is that it clears the plugs. If really rich, it will load the plugs up and they don't make the fire like they are supposed to. Do you smell gassy exhaust when the car starts screwing up?

T Sensor II is on your intake plenum. Finely adjusts mixture via signal to the ECU. Doubtful that that is it, but hey, had to throw something into the post.

A car I was working on would do what yours is doing. Points kept closing up and changing the timing. Reset points and it would do what it was supposed to do which is why I mentioned it. Still don't know reason points would not stay adjusted.

BTW .... when cold the mixture is rich with additional air. As AAR closes, mixture can richen if the CHT is out of spec when warm (still shows high OHMS instead of going to >1000 or lower). Rich idle mixture = lo idle speed

Lets throw another rock and say that the fuel pressure could be high ...

[speed metal army]

Im going to try the CHT.A fella that lives here has the same year ive got and has the same exact issue.Says hes never changed the sensor.
Can I get that sucker out without removing the intake?Looks tight..I know about the ground down extension.

No gassy exhaust when it idles low.

[Cap'n Krusty]

Im going to try the CHT.A fella that lives here has the same year ive got and has the same exact issue.Says hes never changed the sensor.
Can I get that sucker out without removing the intake?Looks tight..I know about the ground down extension.

No gassy exhaust when it idles low.

Considering the relative difficulty of successfully changing the CHT sensor, I think I'd test it first. Failure is a a fairly rare event. Best case scenario is you get the old one out and the new one in. Worst cases include stripping the threads in the head, breaking the sensor off, dropping the new washer before you get it in place, cross threading the head, and possibly other bad things.

The Cap'n

[speed metal army]

Yeah.That does sound like a blast.

Well,Capn,what do you think the deal is?I did discover a slightly sweaty(leaky) injector.But that would be more of a high idle thing,no?
What about adjusting that TPS a shade? (IMG:style_emoticons/default/confused24.gif)

[Cap'n Krusty]

I suggest you go to PB Anders excellent website and download the necessary troubleshooting information, then apply that knowledge to your problem. FWIW, I personally don't think you have a CHT sensor issue, but I could be wrong.

Oh, fix the leaking injector. I'm presuming you mean the hose is wet. If the leak is from the injector body, it will have to be replaced.

The Cap'n

[Tom]

I'd do the easy things first. Keep it simple, as major parts of the fuel injection don't usually go bad all of a sudden, if so it usually won't run at all or very poorly. Things I would be more apt to check: Bad connections, fuel pressure, plugs, timing, etc. i wouldn't go adjusting the MPS or major pieces of the FI system right off. You could "fix" the problem temporarily, only to find out down the road that you misadjusted to cover for another problem.
Tom

[avidfanjpl]

Here is something even more weird.

If your back cylinder passenger side spark plug wire is ANYWHERE near the MPS, if you have one, move it. So, yeah, I am tired and forgot the number of the cylinder. Think it is Cylinder 3, but give me a break. I am worn out from this week.

The spark EMI disturbs the MPS.

Believe me, everyone who has that problem and it is the wire near the MPS, has flipped out on the spot. But I only really know Djet 73/74 cars really well.

You don't know till you look, but it is true, if they are near each other.

John

[speed metal army]

Here is something even more weird.

If your back cylinder passenger side spark plug wire is ANYWHERE near the MPS, if you have one, move it. So, yeah, I am tired and forgot the number of the cylinder. Think it is Cylinder 3, but give me a break. I am worn out from this week.

The spark EMI disturbs the MPS.

Believe me, everyone who has that problem and it is the wire near the MPS, has flipped out on the spot. But I only really know Djet 73/74 cars really well.

You don't know till you look, but it is true, if they are near each other.

John

That is weird.I'll check.

The real mystery to me,is how I create a temporary vac leak,and voila!It idles great again. (IMG:style_emoticons/default/confused24.gif)
Plugs are nice and tan when pulled,and brand new ones installed a week ago.