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Truck runs crappy in warm weather, stutters, loss of power when cruising at highway speeds.  Now it's cold outside, it runs great... has full tuneup done on it. Cannot find any vacuum leaks. Did Vacuum test with gage-all ok. Squirted water all around when idling, no change in RPM. Squirted brake cleaner around manifold and injectors, no change in RPM.  

Any ideas anyone?  

i know its not important.. but ... year.. make.. model and engine type... even transmission might help...

its really hard to take a wild guess if we don't know what kind of fuel system you have .. what kind of ignition...


i have a few things to check...  do you own a digital volt meter??? set it to 20 volts scale..

start the engine .. turn on the headlights..

1.  battery positive post to battery negative post   14.1 to 14.8 is expected.

2.  battery negative post to the engine block...  0.04 volts is expected.

3.  battery negative post to the body....   0.02 volts is expected..

4.  engine block to the body..........  0.02 volts is expected..

if on tests 2, 3, 4  you get 0.00.. change the meter setting to 2 volts DC scale and retest..

please post results.. by number

i would also want to examine the ignition coil..  the exterior for signs of high voltage leakage..   and also for output.. it needs to throw a 3/4 inch spark in a bright blue snappy flash..   depending on the type of ignition you have.. do not pull a wire from a multiple terminal coil pack.. or coil on plug ignition systems...   you won't like how expensive it is to fix if you do this..

you will if you have a multiterminal coil.. want to check the bottom for cracks..  where high voltage can leak out and IN...