Hunting Idle after Install CHTS, & Stock Chip

[MOMO3.2]

My 1987 Carrera 3.2 previously developed a rough idle (Not hunting) and smoking after running for a minute or so.

To address this issue, I changed out my original single wire Cylinder Head Temperature Sensor (CHTS) with the 2 wire sensor. Since I need to get my car smogged, I removed the 911 Chips Performance Chip and installed the stock chip.

Well, when I started the car back up, it seemed to have the same condition of smoking and a rough idle. I decided to take a spin around the block to see if the condition changed as my car came up to temperature. About half way up the block, my car began spewing smoke. It was so bad, I quickly turned back to go home. During that half block return trip, the smoke subsided, so I decided to keep driving. Everything smoothed out and the motor felt very strong. In fact, I drove around for about half an hour and the car just got better and better and actually feels stronger running than it ever has. I am thinking my CHTS must have been bad since I bought the car nearly 6 years ago.

The BAD news is my idle is hunting severely. If I turn the ignition off and restart the car, the idle is fine. If I rev the car even slightly, the hunting begins and persists until I turn the car off and start it again. Moreover, if the idle is hunting and I remove the oil filler cap, the idle settles down instantly and remains steady until I increase revs.

What is going on? Does the fact that the idle returns to steady when I remove the oil filler cap mean that this is a vaccum leak?

This hunting idle is kind of a cruel irony because the car runs better now than ever under power.

Help!

Thank you.

Mike

[ischmitz]

Mike, read here Would changing air filters effect exhaust color? you most likely need to adjust the idle air screw. Check Steve's document. Should be a 10 minute fix on the outside.

It's not getting enough air - back the screw out a couple of turns and you are all set. With the oil cap removed it gets additional air.

Cheers,
Ingo

[stlrj]

Check the two pin connector for the CHT in the engine compartment, it could be bad. Try disconnecting it while engine is running to see if it makes any difference. That should tell you if you have a connection at all.

[MOMO3.2]

Ingo:

Thank you for the reply. I will give the idle adjust screw a whirl today. I am really hoping this is it. Otherwise, wow, my car is running better than ever!

stlrj:

Thank you for your reply. I will check out the connector if the idle adjust screw does not correct my problem.

Pelican BBS ROCKS!

Thank you guys!

Mike

[MOMO3.2]

Thanks Ingo. I was able to get the idle settled for the most part by adjusting the screw. It did come back after I drove for a half hour, but I think I need to work with the setting a little.

The important thing is...It passed California Smog--again!

Mike

[ischmitz]

Great - glad it worked for you. The way I understand it is that you need to adjust the screw until there is no perceptable difference between the jumper in place on the diagnostics port or the jumper removed. I would try that to get it spot on. By the way, the jumper is the same as closing the WOT switch. In other words if you press the WOT microswitch on the throttle body while the throttle is at idle you accomplish the same thing as putting the jumper in place.

The bridge essentially centers the ICV and disables its feedback loop in the DME. Hunting is a result of the PID feedback loop overcompensating when the stable point it too far away from the ICV center position.

Cheers,
Ingo