Runs bad when cold

[mnewman]

1988 Ranger 2.9 with auto trans.

I got this as a non-running truck but it fired right up after I changed the ECM relay. It ran fairly good on 7 year old gas. Just had a small hesitation when you'd hit the throttle. Fast forward a few month and one day it just started missing terribly and the hesitation is now pretty bad.

Things I've done:
Air filter
Fuel filter
plugs, wires, dist cap and rotor
Looked for vac leaks and didn't find any.

I kept messing with and driving it short distances. For the most part it's stopped missing but will still stumble pretty bad. While it's stumbling, if you let off the throttle it instantly clears up and runs on all 6. Eventually if you just hold the throttle it will snap out of it and take off like normal. This mostly goes away after it gets warm. There is no CEL.

What should I check? Trying to avoid the parts cannon. The items I've already replaced where long overdue so I don't feel bad there.

 

[vagabond80]

check your coolant level
coolant temp tells it how to idle when cold

 

[mnewman]

Oil was changed and everything else was topped off so it should be good but I'll double check it.

 

[vagabond80]

I'll elaborate a bit further since rereading, I don't like the way I phrased my first message. I'm sure someone can add more/better detail, but in the meantime to get you on the path...

The coolant temp sensor signals the computer and idle air control valve to adjust for when the engine is cold. So if there is a problem with your sensor or the coolant isn't reaching it, the computer doesn't know the correct mixture to use

 

[mnewman]

Gotcha. I will take a look. I think I saw something in one of the searches about the values using an ohm meter. I know it's plugged in but I didn't really look at the condition of the wires or plug.

 

[Shran]

All great info, coolant/coolant temp sensor is where I would start too. I would also see if you can get a fuel pressure reading. I have had several trucks that sat for a while develop little holes in the rubber hose between the fuel pump and sending unit. Fuel sprays out of that hole and back into the tank instead of into the fuel system so you end up with a low fuel pressure scenario... I wouldn't normally suspect that but it happens specifically on vehicles that have sat with old gas in the tank.

 

[mnewman]

Thanks for the responses. We'll likely never know as I sold the truck tonight. Time to get back to the BII.