Tarscien

I just did an oil change and now I'm having some interesting results. Was using Castrol 20-50 Synthetic before, swapped out to Quaker State 10-30. Car smoked a ton when I first started it up. Couldn't see the front of the house. It idled fine at that point so I took it for a drive to warm up the engine and not smoke out my neighbors.

About 2 minutes into the drive I stop at a sign and the entire car is shaking. I noticed that the oil pressure was low. Really low and the car was idling around 500 rpm. Stop the engine, check the oil level which was fine. Car starts perfectly but is on the edge of stalling when idling. In order to keep the oil pressure where it used to be (around the 40-50 mark) I have to keep the engine at about 3k.

Is this because the oil is thinner and I'm running into compression problems? I never had a problem with idle before I did this change and this is the first change I've done on this car since I bought it.

Any ideas on what kind of fun I might have awaiting me? Should I just go right back to the 20-50?

deadRX7Conv

Dash gauge is a joke.
Thinner oil will typically result in lower oil PSI. As long as oil flow is good, and you meet the oil PSI requirement in the service manual, don't worry about it.

Thick oil can shore up oil pressure in tired engines.
Thick oil will always leak past tired seals slower then a thin oil.
Thin oil might be consumed more but that'll take time to see. Other then PSI, you should not have noticed any difference between the oil weights right away.
Thin oil reduces parasitite drag. If anything, your idle should be higher and engine should rev easier.

If this was the 1st change since you bought it, how do you know/trust what was put in before? Maybe you should've changed the oil before handing over the cash?

Go back to 20w50. If the problem doesn't go away, coincidence just happened. You probably bumped into something while working on the car and caused the problem. Inspect all the hoses and wiring under the hood. Set idle/timing per the FSM. Clean the TB and MAF using appropriate cleaners. Replace the fuel filter and run a couple tanks of Techron concentrate, Gumout Regane, or Redline fuel injector cleaner. Replace the plugs, wires, thermostat and all other fluids/filters that you haven't replaced already.

Tarscien

Thanks. I assume that was the oil being used because there was an empty oil container wedged in the engine bay and 2 more full ones of the same type in the trunk of the car. I'll give it a shot going back to 20-50 and hope that solves the problem. If not then we'll see what kind of magic I can work by replacing everything around it.