Check engine light comes on with no trouble codes

https://www.obd-codes.com/p0172

P0172 and P0175 OBD II Trouble Codes

what is the code your check engine light should blink when you turn key on that is your trouble code ---throwing parts at problem very rarely solves the problem the code can give you the start point towards solving problem

your 98 buick is equipped with an obd2 diagnostic system, a faulty cam sensor will throw a trouble code causing a check engine or service engine soon light. however cylinder misfire or poor signal to coil pack/packs would be a symptom if for some reason the obd2 or ecm was faulty and not throwing a code

When your engine light comes on that is telling you that your computer is setting error codes that needs to be checked.

Suggest you take it to an auto parts store and have the codes read. Make sure you write them down in the order they come off of the scanner since some codes will be fed by other codes.

The difference in fuel type won't turn the check engine light out. You may be on the right track with the new fuel cap, they are very common to set an EVAP code, usually P0442 for a small leak (such as a loose or leaking gas cap). The other problem they are known for is code P0128 for a faulty thermostat, opening too soon. It's still best to have it scanned at a large parts retailer, usually for free, then diagnose the actual trouble code rather than just the symptoms. There are literally 1500 trouble codes for your vehicle alone.

The answer is yes. How long it takes to come back up depends on what the problem actually is. You can reset the computer but the problem still exist and will cause the computer to throw the code back up as soon as it detects it and identifies what it believes is causing the problem. You could have something as simple as a clogged PCV valve or O2 Sensor being bad to something more serious like a leaking set of rings or loose timing belt. Before you reset the computer stop at an Auto Zone or Advance Auto and ask them to connect their code scanner and identify the code that is causing the problem. Most of them do that for free and that will tell you where to look.

Do you know what trouble code the Previa is throwing?
You may want to check the little 1/2 inch diameter passage in the throttle body that connects to the EGR valve. If that passage gets clogged (and it usually does), It'll throw a check engine light. I was having a similar problem and found that this passage was completely blocked with carbon deposits. You can clean it out with a small screwdriver and a shopvac.

If you suspect that your transmission is to blame because of a trouble code, it could be a small problem that has snowballed. My Olds was throwing me the same code. I reset the codes with a code reader, then manually reset the computer by disconnecting the battery.Then after codes first started coming back up, I used the code reader again and found it was the air intake temperature sensor ($15 part) on the air-box. Problem has not re-occurred.

If engine light is coming on, there should be a code stored, and apparently parts stores will give free code scan. Try that, and then you can pinpoint area of trouble, without throwing one part after another on, even if it costs $20 it's worth it.

you need to have the trouble codes checked with a obd2 code reader.
it could be the throttle postion sensor if the car would not accelerate but there is no way to tell for sure until you see what trouble code the vehicle is throwing. most auto parts stores will check them for free. hope this helps