Talking about my 87 YJ with a 4.2 and manual tranny.
I took the wrangler for a ride the other day and came home on the freeway. It ran great through town, very seldom would I get it to 4th gear on the city streets. So I didn't notice any problems. Had a friend looking it over and he pointed out that I had some vac lines that were not the right type of hose.
So I drove it home on the freeway. Only about 18 miles tops. I noticed that in 5th gear it was losing ground. At first I thought it was just because I was going up a slight hill. Not much of one really , maybe 500' up in a little over 2 miles, So not a real hill.
Today I got up and replaced all the vac line I could see with new line. One piece at a time. I did forget on one line which way the plastic piece was in the line. I am only assuming that it is some kind of valve or regulator. It is the one that is circled on the bottom. Plus I also found one hose that was is not hooked up to anything at all. Now I am no engineer, But I am pretty sure that if they made a fitting for it and put a hose on it, than it is supposed to go somewhere. That is the top circle.
Anyway I got this done and thought I would take it out for a quick ride. I got it back on the highway and now I can't get it above 60 and after about 3 miles it starts slowing down. I have a bikini top on it, so it pretty tough to hear the motor above 35 mph. But I am pretty sure that I am hearing knock from the engine, sort of like floating the valves. I slow down enough that I put it back in 3rd and can get rpms and speed back up, but it drops when I put it in 4th again. Never did get to 5th today.
We got to where we were getting off road and took it a couple of miles down a dirt road. Its got some rough spots so I try to hit it a little harder that I normally would just to see what happens. IT does fine even though I don't think it was going in to 4x4 drive. But that's a whole nother thread.
We get back to pavement and now this thing will not idle. It dies every time I put the clutch in. So we have to start it again at every stop sign. Then I started left foot braking and keeping my right on the gas to keep it going. But even now that it has cooled down, it is still the same way. It was idling fine when we first took off after the hose swap out. So I don't know what the heck happened and why I will not get over 60.