86 pulsing at idle

[jeff1hughes]

My 86 tends to pulse at idle, revving up and down from about 600 rpm up to 1700 rpm while it's cold, normally once warmed up it runs well and idles steady, at about 950 to 1100 rpm depending on barometric conditions. Any ideas out there?

[scottb]

Sounds exactly like what my 84 was doing. I replaced the head temp sensor, idle control valve, and O2 sensor. Nothing helped. Then someone suggested I get the mixture adjusted. I took the suggestion, and the idle has been rock solid ever since.

[jeff1hughes]

How does one go about getting the mixture adjusted, isn't that all controlled by the computer?

[scottb]

I have to be honest, Jeff. I took it in to the folks at TRE, and they adjusted the mixture. I don't know the details, but my understanding is that the mixture is adjustable on our cars. Sorry I couldn't be more helpful.

[Lorenfb]

The most common problems for an erratic idle are:

1. idle switch
2. dirty idle valve
3. bad performance chip
4. rich fuel mixture (more common on SCs)
5. temp sensor with too high a value when cold,
especially true on '84 & '85 with old one wire sensor

The O2 sensor won't cause this problem (cold) as the engine
runs open loop (no O2 sensor) until a little warm.

[stlrj]

Lots of ideas out there...just click on the search button.

-Joe