cold start misfire

[wesayso]

I have a misfire (rough running) for the first 15 - 20 seconds when starting my 97 LC. RPM's are ok (1200). After the roughly 20 seconds, misfire vanishes and engine idle is perfect. It's happened the last 5 or 6 times when engine is stone cold. Any ideas? I searched the forum, but didn't find anything relevant.

 

[wesayso]

Anyone?

 

[BILT4ME]

Check plug wires on cap and plugs.

Look at vacuum hoses for brittleness and cracks.

 

[GhettoTank]

I'm with Bilt, I was chasing this issue and took my rig all the way down to the lower intake mani and deleted all the VSV and EGR garbage. It HELPED, but the main issue ended up being a stuffed IACV. Don't go throwing parts at it, but I'd check all your vac lines, and replace them while you're in there to save the future headache. Then test your IACV.

What does your truck idle at warm? does it stumble if you let it idle warm for 5 minutes without touching it? How new are plugs and wires? have you inspected cap and rotor for excessive pitting/wear?

 

[wesayso]

I'm with Bilt, I was chasing this issue and took my rig all the way down to the lower intake mani and deleted all the VSV and EGR garbage. It HELPED, but the main issue ended up being a stuffed IACV. Don't go throwing parts at it, but I'd check all your vac lines, and replace them while you're in there to save the future headache. Then test your IACV.

What does your truck idle at warm? does it stumble if you let it idle warm for 5 minutes without touching it? How new are plugs and wires? have you inspected cap and rotor for excessive pitting/wear?

Truck has a very smooth idle at about 600. No hesitation or misfire after initial 20 seconds. Runs great.

 

[GhettoTank]

Truck has a very smooth idle at about 600. No hesitation or misfire after initial 20 seconds. Runs great.

Very odd. I’d definitely check your IAC as well, I know per the oem schematic is should open wide at startup, but then be between positions 0-3 at cold and warm idle. It may be getting stuck open and then a little bit of engine or electrical load allows it to loosen up.

definitely start with vac and IAC is my vote. Easy to rule out and simple to fix