Im looking for someone who might have had this problem or something similar and how they fixed it. I have an 86 with a 2.5 engine I had removed the engine to fix a broken head bolt which had oil and antifreeze pouring down the driver side of the block. I disassembled the engine and put all new gaskets in it replaced the torque converter while the engine was removed and put it all back together. I replaced all the timing gears, sensors, fuel injector, fuel pressure regulator diaphram, fuel pump and relay and base timed it to 8 degrees BTDC and now I have a truck that starts and runs like a champ until the temps drop down below forty degrees. When cold it almost seems like the timing is to far advanced but when warm it starts fine after running it the truck starts fine until the block cools down over night it also will have a weird whine that will follow the RPMs of the engine until warm. I had a slight stumble on acceleration but I reset the timing today and that seemed to take that out now I would like to get this thing dialed in before it really gets cold this winter.

 

I'm no expert but if its still not fixed, maybe try replacing the coolant temperature sensor?

 

Crack open that hood and give those temperature sensors the evil eye – the ones for the coolant and the air intake. They should be telling your engine's brain how to behave when it's chilly, so if they're acting up, they could be messing with your start-up mix.

And about that whine that's keeping pace with your RPMs – it's worth taking a gander at your ignition setup. Trot through your ignition coil, distributor cap, and the rest of the gang. Even the new kids on the block can sometimes start causing trouble right out of the gates.

 

Just went through a similar CSI-type quest with my 89 S15 Jimmy. Kept getting a MAP error and after tossing all kinds a senors at it. Also found 1 blocked vacuum port and rerouted that hose but the main issue was the ICM. Tested for spark at the plugs and coil okay but the ICM was out.

 

I replaced the coolant sensor with a new one when I first started to have problems and I did replace the correct one on the thermostat housing.

 

Did your S-15 run well with a bad ICM because mine runs great as long as its above 40degrees it just doesnt start in the cold.

 

Yes. Didn't have real issues until the weather turned cold. Had to hold down the gas peddle to start and while idling until warm. Sometimes it would chug a couple of times like the gas stopped flowing. Always kicked back in. Other times it would just shut off completely but would start right back up. Did this for a long time since its not as cold where I am. Finally totally failed last week. I would check yours sparks at the places I did.

 

Check out your truck for any vacuum leaks. These leaks can mess with the air and fuel balance, especially when it's cold, leading to rough starts or idling. Just have a look at all the vacuum hoses and connections to see if there's anything out of place

 

This is true. First thing we did with my Jimmy was smoke test. Found a leak and replaced hose. Ran great for about a week. Then found a clogged vacuum port on the throttle body and had to rerout the hose - not ideal but it worked great for another week until finally replacing the ICM. BUT in the process of tightening everything we forgot to attach the a hose so yeah, vacuum leaks and disconnected hoses will cause problems.