Need Brilliance.

What do you mean by "the pump is working"? Was there a low pressure reading when read with a mechanical gauge? If not, then you are likely just looking at a bad oil pressure sender which is minor.

As in my question above, The sending unit was replaced. Mechanics thought that fixed problem. Did not. Then they idled truck all day on mechanical gauge. They said couldn't find the problem. Had mechanic take truck home, didn't experience problem. This was months ago, have since lost job, have no money. The problem has gotten worse since then. When IAC valve was replaced, it was a question of whether was oil pressure or idle. Idle does not change, only oil pressure. This does not happen when cold, or when truck is moving, only when stopped and at idle. I can not do stop and go traffic, as truck is manual trans, and only have two feet. Please help.

This isn't a big mystery. The mechanical test either proves there is no pressure problem or it doesn't. If it proves that you have low pressure, then you probably need a new oil pump. If you're putting cleaning solvents in the oil, then you're making the problem much worse. If the mechanical test proves the pressure is OK, then you simply have a gauge problem.

Is this really that simple? Wouldn't oil pressure drop when engine is cold? Or truck is moving? Why is only when stopped and at idle? Please explain, I need to understand.

The lowest pressure is always at idle because the pump is at it's lowest RPM and the warmer the engine, the lower it gets as the oil gets thinner from the heat. Your only concern is that it never drops below about 5 to 8PSI

So, the oil pump is bad? Thank you for taking time to answer.

No, I never said that. You still haven't told me what the lowest pressure reading that was taken with a mechanical gauge was.

I don't know what readings were, only that I was told the oil pump was fine. They leaned towards sludge in sump, which is why the solvents were used, there was a lot of gunk. To clean sump any other way involved pulling engine, just couldn't afford. I thought that if oil pump was problem would have symptoms all the time, not just hot at idle. One of those either it works or it doesn't.

If the inside of your engine is sludged up, the very worst thing you could do is use a solvent that will loosen it up so it can travel into places where it can cause real problems. Either the pump is maintain sufficient pressure or it isn't. If sludge in the sump was your problem, the result would be low pressure even with the mechanical gauge. So again, either the pressure reading is sufficient or it isn't.

Ok, so what you are saying, is I need to do mechanical gauge now. Wish I could, but can not afford. Am broke. IS there a way to tell at home, without gauge? Without blowing engine? No, they weren't saying engine sludged up, they were saying sump sludged. Warmed engine, turned off, added 1 cup kerosene to oil, ran 5 mins, then drained oil, changed filter, put new oil in. the semi-solids that came out were nasty, this was repeated again. Last oil change, no more yuk. Am woman, in case you couldn't tell. Was advised this by 3 different Ford mechanics, now you are saying was bad to do? I always did my maintenance, never more that 3000 miles per oil change. The only problem ever had was loss of coolant, This engine had bad seal, was replaced early on. Never had any sign of coolant in oil, but do continue to loose coolant, slowly.