My 85 has started idling rough at cold start staying around 400-500 rpm then dying if I don't give it gas. After 10-15 sec warmup the idle and startup is normal. This started after replacing the radiator, which developed a leak at the outlet. Ran hot once with just rinse water in the cooling system with the old radiator after a flush. Yesterday I took it on the freeway and could not get above 70mph. On the same stretch of freeway today it had no problem getting past 70, even up to 85 on flat road and slight incline which is normal for this truck. So I don't know what to make of that but right now I just have the rough cold idle, no noticeable loss of power, coolant/oil mixing, leaks or any smoke. Worth noting I did not replace the thermostat, but currently have an OEM one I put in 4 years and 60k miles ago. Any suggestions on what I should check now? I'm planning to put a new sankei cap on to replace the oreily's I got in the pinch and to look at the plugs, check compression to start out.

 

I did a compression check this morning, not too good, not too good:

#4- 100
#3- 115
#2- 115
#1- 115

I put some oil in cyl #4 and the psi went up. I also noticed a vacuum leak at injector #4, no external fuel leakage I can see, but I can hear air getting sucked in at the grommet behind the connector. If I cover the grommet with my finger the hiss is muffled. Can a vacuum leak at the injector affect the compression reading? Would it be completely crazy to put rtv around the leak until I get new seals?

I'm actually surprised at the compression results for how well it seems to be running. I pressed the gas pedal down to the floor while cranking but noticed later that my throttle cable was a bit loose, so the throttle was not 100% open, more like 80-90% compared to when I hold the throttle open at the throttle body. Could this make a significant difference in the compression reading?

I screwed in the idle adjust in and it seemed responsive and killed the engine. Battery reads 12.2V.