Buick lesabre 90 engine lopes at an idle and tends to lose power then resumes to run normally. Almost like water in fuel and or bad timing. both of which have been eleviated from cause. It will be appreciated if some could give me some idea's the manual may not cover? thanks

You may want to check the intake manifold coolant port tube, which is plastic and tends to get eaten away over time on this particular engine. This condition causes coolant to mix with fuel in the intake manifold, making the engine run rough, and ultimately not start.

The replacement tube is metal, and will solve the problem. A good mechanic will insure the intake is clean and dry during re-assembly.

Sounds like the throttle body is sticking. Do not use WD40 to free it. Use some Carb cleaner on it and then oil it with some synthetic 5w30 engine oil. You may also have to clean the MAF and MAP sensors if this is fuel injected. I had a 2000 Buick Lesabre and the glue came off letting in water when driven in the rain. It would cut out till the heat from the engine dried out the water and then it would work again.

I saw exact same problem for few days. Now I see check engine light all the time and engine speed is normal.
The cruise control stopped working. Cruise control sign so nOT light up when I turn it ON. Nor does it works.
But car seems to work fine.

fuel pressure regulator!! vacuum run not electric!! happened to my 97 lesabre

Sounds like low fuel pressure. i.e. fuel pump, fuel pressure regulator, or fuel filter.

did you clean the idle speed control air bypass valve?, u do this by spraying carb spray into the intake while the engine is held at hi idle so it won't stall, use up about half the can, then shut down and disconnect battery for 5 minutes to reset system idle learn, drive the car for a few days and let me know if the problem is fixed.

it could be a plugged fuel filter so try some STP gas treatment and if the condition gets better with that then change the fuel filter

Oil pressure might actually be a bit high for idle. High or low oil pressure in an older engine tends to be indicative of some serious issues. Oil pressure that is too high tends to be a clue that you have serious carbon build up. That aside, have you tried running a higher octane fuel, or perhaps adding an octane booster to your normal grade? Pinging can become knocking in a badly worn engine. One recommendation: At your next oil change try substituting a quart of marvel mystery oil or lucas engine oil treatment in place of one quart of your normal oil. Both have some pretty good track records for helping to free up sticking valves and break up carbon in older engines. I'm an old timer myself, and I personally swear by Marvel for older engines. There is no "rebuild in a can" but Marvel comes close. Give those a shot, let me know what happens.

try cleaning your idle control valve, make sure you dont have any codes in your computer, if you do address those codesl