Okay my service engine soon light doesnt come on unless im doing 60 for a little while and as soon as i hit the interstate getting up to about 70 my service engine soon light comes on, and ive told my machanic which hasnt had time to get around to it, because he was fixing my idle issue. But does anybody know why this comes up? Because my friend told me something in the computer needs to be reset or something because if not it will keep throwing the code, which have no clue yet, the only code that we could come up with is bad o2 sensor which was replaced and a bad tps, which i also replaced and i just had a distributor installed which solved my idle problem. I dont really understand why the light comes on, if i cruise around town the light never comes on. Its only when i hit the freeway, the only thing i can think of is the transmission, because sometimes when i get on the gas enough it doesnt like to downshift into third, it just stays in fourth on the freeway unless i slow down to 40, but then it automatically when to shift right back into fourth and not do nuthin. Also i have another question. What is the proper oil pressure at idle??? i know im do for another oil change about now, but the car ran great for about a week when i got the idle fixed, but now its still idling fine but its hesistant. like if the oil gauge shows around 30 it shakes just a little but and little around 28, it doesnt really feel smooth until it drops down to 26. But my friend told me that was a little little low. He said you dont want it anywhere below 28. Is this true? Im sure the car maybe needs another quart of oil anyway, but i just thought i would ask. But when its around 30, it seems hesistant with more oil pressure, but once it drops a little between 26 and 28 it seems smoother.

 

You need to get a paper clip and follow the "code retrieval" procedure described in the FAQ or the tech articles on this website. Without knowing what code it is, it could be a few different things. My guess would be the EGR. The computer doesnt monitor the transmission for problems.

Oil pressure should be in the 45-60 PSI range while driving. You might have a bad sending unit showing the wrong value on the dash. On your '91 its the black canister just above the oil filter. They fail about once every couple of years.

 

If you replaced the o2 sensor and still get an o2 sensor code, you might of lost the ground for the o2 sensor at the ecm. Thats what happened to me on my iroc. I had an o2 sensor code, replaced the sensor and still got the code. Hooked my scanner up and the o2 sensor values stayed at .45 volts all the time with no switching. Probing around with my vom, discovered my o2 sensor didnt have a ground at the ecm. Made a new ground and no more codes. But like what Kevin91Z said, you need to check your codes to see what it is. Your oil pressure seems normal to me if thats a hot engine reading. Mine with a hot engine and idling, its at 15 psi and when its cold, it like 60 psi and bottoms out at 15 psi as the engine warms up.

 

I agree to check for the codes first,Bring the car up to speed and set the codes,see what code or codes u get.I have a gm sevice manual so i can check from there and give u some direction to go in.I just used the manual lastweek,it led me to ecm and i had to change it.Runs great now!!!

 

okay i will do that, i believe the egr does need replacing, people have told me to replace, i just never have. And as far as the o2 situation, it seems fine, it was professionally installed, but ill look into it. As for the oil pressure the lowest mine will ever go down is 26 at engine temp. Cold its around 34 at idle, starting mine up in the morning my gauage nevers gets to 60, it fets to 50 max i believe. then goes down to 34 then 30 then 26. Im do for an oil change, i look at getting a new oil canister. I only asked on the transmission situation because when my transmission was screwed at one point and it didnt run right the light came on and off, because the transmission was slipping at the time, and when it seemed to work the light was off, and when the tranny was acting up the light came on, so idk thats a mystery to me, unless im in need of a new transmission cable.