Any oldschool obd1 mechanics here i need help with a diagnosis

[YarisSedan]

Originally Posted by GeneW

Could also be the Oxygen sensor, a borderline condition that does not trigger a check engine light but may be deranging mixture settings enough to cause the system to target something else that governs mixture.

There may also be issues with exhaust gas recirculation, if the vehicle has such a device, since carbon deposits may have broken lose and stuck it open or closed. I think most modern cars use an EGR because it reduces pre-detonation and improves NOx emissions by changing the chemistry of the combustion.

Another, more awful possiblity, is that you've compromised oil control by loosening up some carbon around the oil rings and now you have blow by. Easy to check, run the engine hot and see if there is "puffing" when the oil filler cap is removed, in really bad cases the dipstick holder will also "puff" blowby.

Another possibility is that your carbon removal trick has clogged the catalytic converter. You can test this problem by driving the vehicle under load - like up a hill - it will lose power rapidly going up hill. A clogged catalytic converter will cause issues with idling too.

Gene

I was thinking some of those things. I dont belive the cat is clogged since seafoam is usually supose to clean the cat. EGR malfunction is possible since a egr comming on at idle will cause issues.

I think tonight or tomorrow ill remove the throttle body and clean the iac valve first before anything. I am hoping that does the trick. I am changing the spark plugs since i have the intake off since they are worn and the incorrect one even though i dont think its the cause of the problem.

Hopefully that takes care of it. If not i guess egr is next step. I am glad there are many mechanics here on ayrisworld to bounce ideas off of. Its liek a real world house episode but with cars =)

[GeneW]

Originally Posted by YarisSedan

I was thinking some of those things. I dont belive the cat is clogged since seafoam is usually supose to clean the cat.

If you're still having issues after you've tried some things, reconsider the cat converter. Worst times I've had troubleshooting was when I assume that things were "not supposed to happen" and ended up happening.

Gene