90 1.6 losing oil pressure

I recently acquired a nice 90 with 179K that runs great except for the oil pressure. when it first starts the pressure is around 60. When warm and idle it is around 15-20. while driving it seems to hover around 30ish. But sometimes while coming to a stop the oil pressure will drop and the car will stall. It does restart but then the car will not idle and stalls repeatedly.This goes on for a minute or two then it oil pressure recovers and everything seems fine. I am running 10W30 and had the oil changed last month. I do not know the history of this car.Also i have noticed that before the oil pressure takes a dive if you run the Heater/AC fan at full speed the car will stall. Any thoughts.

I'd lean more toward the IAC valve on your stalling issue.

Good stuff here -> http://www.miata.net/garage/isc.html

Your oil pressure numbers sound fine. Oil pressure numbers are directly related to engine RPM and the viscosity of the oil. The oil thins out as it heats up so the numbers will drop as the engine reaches normal operating temps.

+1 on checking the IAC valve as that will cause the engine to stumble.

The stumbling will cause the oil pressure to look worse.

RJ

thanks for the advise, can i test this or do i just replace it?

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Originally Posted by bodeth

thanks for the advise, can i test this or do i just replace it?

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Click on the link, lots of good reading and pictures available! ;)

Link -> http://www.miata.net/garage/isc.html

thanks i will keep you posted as to what happens..

Run a bottle of Techron Concentrate first, and make sure you don't have a fram filter.
IAC's are not cheap.

Check for vacuum line connections as you may have one off or cracked, this will cause idle issues. You might also look at your plugs since you have a lot of miles on the car for any suspects in oil consumption that may be causing misfire.

Gary

I was able to just hose mine down with some carb cleaner and it ran like new afterward.

of course this was after weeks and weeks of wondering what was wrong with my cold-start enrichments.

Already some good advise about the idle problem, but IMO you're using too thick oil also. 5w30 is as thick as I would go, especially on a street Miata.

Once you get the idle problem fixed, if you still have some odd readings on the oil gauge, I would check the sending unit first. They are not known for being accurate; hence changing to a dummy gauge in 94. Currently my oil pressure gauge flakes out on occation. I know it's the gauge cause I had the engine rebuilt last year, not to mention the notoriously noisy lifters would be freakin loud if my psi dropped to zero!

Just my ::2Cents::