Strange hesitation/stumbling on throttle tip-in when cold
Just thought I'd post here about a problem I've been having w/ my '95 Disco.
The engine has this strange hesitation on initial throttle tip-in, but this only happens when you start the engine after sitting overnight. There have been a couple times pulling out of the driveway where the engine hesitated/stumbled enough to stall. If you keep your foot on the throttle, it will stumble/hesitate for a second then 'clear up' and you're on your way. And it only does it pulling out of my driveway, and for the first few stop signs in my neighborhood.
Once the engine has run for a few minutes, the hesitation disappears and the Disco runs just fine and dandy. Subsequent restarts during the day are not affected by this strange hesitation - it only happens after the vehicle has been sitting overnight.
So far, I've checked the timing and vacuum advance, changed the spark plugs, wires, cap and rotor, fuel filter, replaced some leaky vacuum lines, and checked the coolant temperature sensor resistance. All seems ok there.
I've got a feeling that I might have a problem with the IAC (idle air controller) valve. If you rev the engine slightly on initial startup, the idle speed will drop too low and will take a bit before settling on high idle. As it warms up, the idle speed starts to come down - settling at a fairly normal 750ish once fully warmed up. I'll probably pull it out and see if it needs cleaning...
What do you guys think?
1995 Land Rover Discovery
2004 MINI Cooper S
1994 Jeep Cherokee Sport