When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Everyone was so helpful with my last question so I thought I'd pose a new one to see if I can get some support.
1986 Oldsmobile Cutlass Supreme with 3.8L V6. Just did some routine maintenance (spark plugs, wires, etc) and I just noticed the CHECK ENGINE light will come on occasionally. Talked to the wife and she said it has been coming on for several weeks. It is intermittent though and comes on for a little bit, then goes off. She said usually when idling like at a red light. It doesn't stay on and doesn't come on when you first start the car. It comes on after a short time (5 minutes) but does go off.
I stole this directly off the Internet. It may be of some assistance to you. Most likely (generally) it's often something related to the EGR/Emissions system. Suggest you perform additional on-line searches for 1986 Oldsmobile Cutlass Supreme 3.8L intermittent check engine light. Most likely if your owners manual doesn't list the codes, you can most easily search for the code(s) on-line.
Your Vehicle: 1986 Oldsmobile Cutlass Supreme with 3.8L V6
There are a lot of different things that can set a Check Engine light intermittently. This could be a failing Oxygen Sensor, a problem in the Emissions system, etc. We will need those diagnostic trouble codes. Once the light is set, for however short of time, the code will be stored in the on-board computer. The codes can be retrieved even if the light is currently off. On this vehicle, you do not need a scan-tool, and can retrieve the codes using the procedure below. If you can obtain these codes, I am certain I can point you in the right direction. The DLC port is located under the driver's side dash.
-Insert a jumper wire into terminals "A" and "B" (connecting the 2)
-Without starting the engine, turn the key to the ON position.
-The Check Engine light should now be flashing codes- ex: (blink)(blink) pause (blink)(blink) = Code 22
Last edited by Vintage Chief; September 17th, 2023 at 04:55 AM.
Unfortunately an intermittent light often means that the codes are not stored. I've found that on the CCC cars, this can be caused by low coolant level that causes air pockets. Of course, there are a dozen other possible causes. The only way to know for sure is to drive around with a scan tool in diagnostic mode. My OTC Genysis will capture data when a code is triggered, which is helpful for finding intermittent problems.
I just put a new battery in it, so I'm wondering if the codes are not gone until I drive it enough the light comes on again. Let me run it a little bit this afternoon and I'll check for the light and then pull the codes.
joe_padavano - Joe can you give some more details on your diagnostic tool? I see you mentioned "OTC Genysis" and I found a lot of different types when googling it. I do appreciate the help.
I'm still having the intermittent service engine soon light pop on. It usually does it when I'm stopped (or parked) but with engine idling. It will turn on for about 20~30 seconds and with no input from me (engine rev, etc), it will go off. I've tried the OBD 1 port but no codes, as I thought there wouldn't be because the light is not on constant. I just changed the antifreeze and made sure no air bubbles. I'm just curious what it could be???
Bad TPS (Throttle Position Sensor) is a likely candidate as they deteriorate over time. I've never done this, but perhaps a thorough cleaning of the throttle body itself?
Good thought Vintage Chief. I'll investigate that idea. Have you ever replaced one? It is INSIDE of the carb right? I'll have to take the top part off if I remember correctly, but not too difficult of a job.
I have not replaced a TPS on your vehicle. I have replaced a couple TPS on other vehicles I've owned. They were basically plug-n-play, but don't take my word for it on your vehicle.
Another piece of information - I've never seen it come on when driving, but my wife said it has come on when driving, but I don't drive it that much and haven't seen it when driving, only when parked idling.
Reviewing some threads/posts suggests a Code 21 often is associated with a failing TPS. I think you said you have no codes. But, I wouldn't necessarily put all my faith in the fact your TPS is good just because it doesn't throw a Code 21.
Good point Vintage Chief. Overall the vehicle is running great with the exception of that intermittent engine light. I've done a bunch of general maintenance things and I'm going to replace the fuel filter this weekend. I may study the TPS. To my knowledge the TPS has never been replaced and at 160k-ish miles and 37 years old, it's probably time. You have given me good info to read up on. Thank you.
If you perform a Search of TPS on this site (any page top right-hand corner) you'll note there are about 4-5 pages returned which all demonstrate "TPS" - not all are related to your specific issue; however, I noted that several demonstrated the TPS is a known failure on this vehicle. Good Luck.
September 17th, 2023, 01:23 AM
Well damn it, Jim! 
