Idle Dropping Fast When Engine is Cold
 

I have had this issue for a while.

Morning start-up, driving away and depress the clutch my rpm needle drops rather fast, but does not die. Now, when the engine is warm depressing the clutch, the rpm needle falls alot smother and makes shifting easier. Could the CHT be the culprit?

I know I am going to hear about the "Vacuum leak", but is there any chance this sensor may be the issue?

BTW, 86 Carrera so Motronic management.


Thanx,

Lots of things...the first I'd check was my AFR/CO...a rich afr will do exactly as you are indicating.

Sure sounds like a Vacuum Leak, sorry could not help myself.

When you say drop, drop to what RPM?

But in all seriousness. when cold after initial warm up idle. Leave the car on and remove the oil filler cap. If she dies, you have a major vacuum leak. If not then +1 on verifying AFR with a LM1 or LM2

Not likely CHTS but check the OHMs, you never know. :eek:

I have an LM1 on hand and the AFR is right on the money. Now, when I remove the oil filler-cap, the engine drops and feels like it's gonna die, but then comes back.

When was the last time you ran a bottle of injector cleaner (techtron/etc) through your tank? Was having this issue at the beginning of the fall/winter (just as it started to get colder) and it resolved after I ran through 1/4 a tank post-techtron.

Oh Good, then next I would check the OHMs on the CHTS.

BTW, when was the last time you changed the fuel filter?

What about the Idle Control Valve? Wouldn't that be in the mix if this is happening when the engine is cold? OP, you can clean it by spraying carb cleaner through it.

Thanx for all of the feeback. The fuel filter is newer, the ICV has been cleaned out very well and the idle is always on the money whether the engine is hot or cold. I have used Techron, but this has never help to resolve this issue. The OHM test for the CHT is something I have not tackled.

BTW, the RPM needle drops to the 750 mark and stays put upon depressing the clutch.


Serge

I would have guessed you're crazy rich but you said the AFR's are rock solid. The odd thing to me is when you drop about 130 Rpm I would think your afr would change since something is changing to cause that. Either air of fuel. What is your Idle AFR just out of curiosity?

Cab,

The AFR is at 14.7.

Reviving this thread as I might of found my culprit!

I decided to take apart AFM to see if anyone PO had messed with it, and I do see that they might have moved the "Dial" 5 teeth clock-wise. Now, would this mean that it is running Lean or Rich?

One of the other symptoms is that the car once warmed, has a tendency not to "freely" coast when in the lower gears, especially in first gear. It feels as if it wants to suddenly slow down.

Here is a pic!
 

i don't know about CW or CCW but if the spring gets tighter, its running leaner. this keeps the flapper from moving more.

the ICV should vibrate with key on and engine off.

check the throttle switch.

if someone has "adjusted the mixture" this way, there is something else going on.
resistor tracks on the AFM may be something to keep in mind.

what is the AFR idle, warm and cold and driving steady.