Surging idle, 1994 V6 Chevy truck.

[Redneck7]

1994 V6 Chevy, 4wd, 5 spd.

Friend's truck started sputtering and cut off this morning and didn't start back up readily. He somehow deduced it was the fuel pump between him and a friend. I got there and helped him drop the tank and put a new one in.

Fired right up when we finished and idled fine for a about a minute. After that minute it went to surging from a high idle down to just about cutting off and back again...

Any thoughts? Fires right up every time, doesn't seem to have trouble running down the road, but won't idle correctly. Did we replace the fuel pump for nothing? It wouldn't start at all prior to replacing it and now it fires right up, so I assume not, but it idled fine before replacing it, even when sputtering...

Any thoughts?

[TerryD]

Saw a throttle position sensor do that in a Honda one time. I've never heard about a Chevy doing it though.

[hklvette]

is it driveable other than the idling problem? If it is drivable, does it still sputter going down the road? If not, I'm think IAC might be flaking out and can't adjust properly at regular idle. If it sputters while driving, I'd guess fuel filter or very dirty injectors.

[Redneck7]

Held at a steady throttle sitting still it will hold a constant RPM with only a faint miss every so often that may have always been there. (you don't hear the motor stutter, you just hear the miss in the exhaust). Driving feels "normal" for a truck that old. Problem seems to just be at idle.

Any idea how the fuel pump worked into all this?

[TerryD]

The miss you are hearing is the EGR valve operating like it should.

[Redneck7]

He replaced IAC this morning, said it "helped, but it still ain't right."

He followed that up with something that rhymes with duck it.

So I reckon we're done repairing this one for a while even though it isn't fixed.

[hklvette]

The miss you are hearing is the EGR valve operating like it should.

EGR at idle? That's new to me.

[TerryD]

The miss you are hearing is the EGR valve operating like it should.

EGR at idle? That's new to me.

Held at a steady throttle sitting still it will hold a constant RPM with only a faint miss...

[dgerm]

Has he thought about seafoaming it? It might help by cleaning out the injectors. It made mine idle a little smoother and I only had 26K at the time.

Tried it on my friends '98 explorer and we caught black gunk with a towel behind his exhaust pipe

[ford150]

just had a dodge dakota doing this due to low voltage.... was only charging 10.5 ..... something to think about