The past two days I've had cold starts. Not snow or anything, just very brisk.

Starting was okay, but to drive is to experience lots of power loss. Driving slowly is perilous, no power then bursts of power, on the highway you lose speed and then it comes back again.

Is it the cold or something else? Yesterday it went away in time, I haven't driven far today - about 15 miles - and it's still there.

 

Vehicle info may help. Injector intermittently working, Fuel pump loosing pressure. Any codes?

 

1990 B350...

I don't know about codes. Yesterday it got so bad that I thought I wouldn't make it up a hill, but by the end of the day it was running really well. Then I climbed to 8600' with no issues, but at the top it started again. Down onto the lower ground (4000') it was okay.

Could it be the fuel filter?

 

Possibly..... but, I don't think that would be affected as much by altitude....

 

Putting a fuel pressure tester on it would tell you whether something is going on as far as the pump or filter. If the filter isn't inside the tank it wouldn't hurt to change it and it should be fairly easy. Might think about a map sensor or the temp sending unit that sends that signal to the ecu. Another thing would be to check all your connections and that includes grounds and make sure the battery cables don't have any green corrosion growing in them.

 

Let me tell you a story .... Just joking.
I have a 1993 Caravan that the fuel pump died and it was difficult to diagnose .... It worked in the night time when the roads were cool .... day time when the roads heated up, it quit pumping.
The heat off the blacktop radiated up to the fuel tank and while the pump was running .... it just lost suction and did not pass fuel.

We were on a trip from Washington to New Mexico ..... same time it was over the weekend and when we tried to find a fuel pump it had to be ordered and delivered in a few days.

As long as we drove at night when the roads were cool .... we made it all the way from Albuquerque to Seattle with a bad fuel pump.

This was a 1993 Dodge Caravan .... I had a 1992 Dodge shadow that died the same way, My Uncle had a 1989 Caravan with same issue .....
When the 1990's Dodge fuel pumps die .... they die in a strange way .... A Ford or Chevrolet just stop working and you get no further down the road ..... A Dodge just kinda keeps working.

If your fuel pump has not been replaced it is time to think about it.

 

This morning it was playing up...

This afternoon it performed perfectly.

I'm wondering if there was some water got into the tank at a refuel a few days ago.

 

And this morning it's still okay...

Not as cold, but still morning.

 

My experience with water in the tank was a long time ago .... The car would run fine .... then randomly pick up the water and the engine would run like crap.
A good example would be on the freeway and going to pass a slower truck ..... you got the pedal to the floor and you are moving some fuel quickly .... get up alongside the truck and it would crap out on me and end up pulling back in behind the truck .... very frustrating and took a long time to figure it out.

I finally thought about water and I put a $1 bottle of HEET in the tank, it enables the heavier water to mix with the gasoline and you just burn it all out ... next tank of gas and it is all gone and runs fine again.
Maybe it is water and maybe not, just put in the HEET and see if problem goes away.
It wont hurt anything and may help. I use to add it to all my cars once a year or so just in case there was condensation or something .... not done it for many years though.
Today I run a can of seafoam in the tank once a year to help keep things clean .... do not think it will help with water though.

 

I'm pretty happy now, it has all come good. Two full days with no problems.

The 'water in the tank' theory seems about the best at this time.