Idle "hunting"

[mejulihn]

I know this topic has come up several times before but here's my story...
After my 2.0 with stock FI has warmed up, I have started to get the vexing "hunting idle". Adjusting the FI mixture adjustment on the ECU box or the idle speed on the throttle body seems to make no improvement. But, when I unplug what I believe is the two-wire plug for the cold start injector near the throttle switch the hunt goes away. One last data point: on cold start the engine fires up immediately and then dies once. On restart it holds the idle speed fine until warmed up. What gives?

[JP Noonan]

What I think you are actually unpluging is the intake air temp sensor (temp sensor I). This is an old "trick" I told that mechanics use to richen up the mixture. It is a band-aid solution, but not a bad one. Problem is if you are only lean at idle this trick richens up the whole rpm band.

Most likely you have a vacuum leak somewhere, not fun, but it can be fixed. You can try to track it down with carb cleaner, but on cars as old as ours I just replace all the hoses and gaskets. Also I use RTV to seal the seam around the sheet metal intake (thanks to DD). The seam is only spot welded and tends to leak over time. One the intake gaskets I use a spray on copper gasket dressing, and use new phenolic spacers.

Also check that the resistence from the CHT sensor is with-in spec.

[mejulihn]

Thanks, JP. Your diagnosis may be correct even though I have already replaced most of the vacuum/intake hoses and seals you mention. The two-wire plug I have disconnected is located about two inches directly below the plug to the throttle switch. The plug looks identical to the ones connected to the four injectors. The temp sensor I think you are referring to is the one attached to a bracket on the case below and to the right of the throttle body. Does that help?

[Dave at Pelican Parts]

What you are describing, the part sticking up out of the manifold (plenum), is indeed the intake air temp sensor, AKA Temp Sensor I. The part that is next to the manifold is the thermo-time switch. It helps operate the cold-start valve.

--DD

[mejulihn]

I took a closer look this morning and the Temp Sensor I is indeed what I am referring to. I found that one of the two wires to this plug was connected by just a few strands of copper and repaired it.

[This message has been edited by mejulihn (edited 10-07-2000).]