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. Any suggestions on what I should check out? I'm planning to look at the plugs and 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 air leak at injector #4, no external fuel leakage I can see, but I hear air getting sucked in at the grommet on the connector. I'm wondering if silicone could hold up there until I can get new seals. I screwed in the idle adjust in and it seemed responsive and killed the engine. Battery reads 12.2V.

 

engine hot? throttle body flap propped open? pulled the efi fuse? what did the compression reading go up to with oil added? what do the plugs look like, in particular #4 vs. the others... how much oil is it using per 1,000 miles?

yeah #4 at 100psi sounds like it's over the generally accepted 10% variation, but depending on oil consumption and such you might be able drive it for awhile longer.

good catch on that leaky injector gasket, maybe clean the dirt/grease off of it and try gooping a loop of rtv all around it, interesting idea let us know if it works.

 

I warmed up the engine but did not pull the efi fuse and I pressed the gas pedal down rather than prop up at the throttle body. My throttle cable is a bit slack so it didn't get 100% open, maybe more like 80%. After adding oil to #4 it read 170. It really doesn't go through much oil at all unless I'm driving for hours on the freeway but that was before the overheat so I'm not sure where it's at now. It was around 1/2 qt every 1000 miles if I was freeway traveling I would say.

Here are the plugs in order #4 at the top:

 

#4 went from 100 to 170, just from adding oil? i wouldn't have expected that much of a difference, but then it's been awhile since i did that.

with the other cylinders at 115, it would have been interesting to see how much of a difference oil would have made there.

that spark plug does look a bit worse, this would probably be the point where a leakdown test might be a good idea.

oil consumption was decent tho.

 

When I did the wet compression on #4 I tried to "spill" the oil in to get the bottle around the heater hoses, then cut up a plastic jug to make a compact funnel and put a bit more in, all in all it was too much. It took a while to burn off and killed my compression gauge in the process so I had to stop testing there and I think this may have affected the reading on #4. Leak down shows the engines not holding pressure and there is combustion gas in the cooling system. Sounds like head gasket, or cracked head at least, and now I'm trying to see what I can about the bottom end before pulling the head. The machine shop said compression testing with a blown head gasket is unreliable, but what throws me off is that all cylinders are low, rather than just one or two. I might try a wet compression test again with a new gauge to get an idea of how the rings and bore are. I checked ignition timing before and after this all happened and it was OK, so I don't think cam timing is off.