Fixed Rough idle, poor driveability

[tonysilva530]

Haven't been here in a while. Just thought I'd post a piece of info I learned while doing a head gasket replacement on a 4.2

After replacing the head gasket and getting everything buttoned up, I started the engine and got a very rough idle and the engine didn't have too much power. (I bought a replacement cylinder head and knew the head was good as I had it completely rebuilt). This HG replacement job kicked my butt the whole way thru. The timing chain set up....the cam phaser.....that dang plastic intake manifold!!!!


Anyhow, I forgot to hook up the engine coolant temperature sensor, and with that sensor disconnected, the ECM defaults to running the engine as if it is getting -40*F intake air temperature. And the ECM trims fuel delivery to work with (what should be) the proper a/f ratio. So, I find out that the plug is not connected to the coolant temp sensor.....I hook it back up and immediately the engine smooths out.

So, well, this may be helpful info if someone has a faulty/nonfunctioning temp sensor and a rough idle.