1998 yukon Mystery p0300 and rough idle still

[OilBurner2003]

Any coolant loss?

You may have mentioned it in another thread, but I forget stuff all the time. If you don’t mind, try to keep to this one thread. Makes it easier for people like me to keep track of things

I do have a little bit, but it’s only from the heater hose that had a cracked retaining clip. Probably doing that today. Oh also, I was on a good stretch of road and went around 70. Felt really good until I hit 70! Then it started shaking. To my surprise, it wasn’t a p0300 like it once was, this time it was a p0140. Got me really confused. I never even got a misfire code, but I’m pretty sure something was misfiring. I’m currently replacing the MAP sensor because I may or may not have snapped off the old one trying to remove it.

One other thing I realized today is that there’s a slight ticking sound that I can’t pinpoint on the passenger side of the engine, I always thought it was a bad spark plug wire when I replaced it, but can still hear it after I fixed all the spark wires. It almost sounds like it’s coming from the exhaust manifold or the valve cover, I know it could be a exhaust leak, but I feel the need to mention it.

 

[OilBurner2003]

These engines have a history of the intake leaking. Another "basics" test that I should have remembered about and can cause multiple misfires. I personally use a water squirt bottle, like what you use on plants, but other use carb cleaner and spray along the rails. I like to check from a cold engine till is warmed up. The smoke method you mentioned, may not be accurate depending on engine temp. Water will not catch fire put carb cleaner can. I have even seen where a repair was done by slightly tightening the intake attachment bolts.

I have heard of the carb method, and you’re right, probably smart to do that on a cold engine.

 

[east302]

The P0140 is a downstream oxygen sensor code (I forget which bank) but shouldn’t impact the air/fuel calculations by the computer. Check if a wire is rubbing against something or is damaged. The service manual has the diagnostic procedure for determining the cause of the code.

 

[OilBurner2003]

The P0140 is a downstream oxygen sensor code (I forget which bank) but shouldn’t impact the air/fuel calculations by the computer. Check if a wire is rubbing against something or is damaged. The service manual has the diagnostic procedure for determining the cause of the code.

I’ve had this issue before, replaced the sensor and it went away for months. I’ve checked the wire and there’s no damage. I’m just wondering why only that code showed up

 

[OR VietVet]

Very well could be the cat inefficiency as well or a failing sensor. What is the sensor? OE? Off brand? Age?

 

[Fless]

P0140 is B1S2, downstream sensor on the driver's side.

 

[OilBurner2003]

Very well could be the cat inefficiency as well or a failing sensor. What is the sensor? OE? Off brand? Age?

It is a WALKER o2 sensor, recommended to me by my mechanic

 

[OR VietVet]

Genuine GM, AC Delco or Delphi

 

[OilBurner2003]

Genuine GM, AC Delco or Delphi

I’ve been told that by other users too

 

[east302]

If it’s in the wiring, you may have temporarily “fixed” a marginal connection simply by moving the wiring around when you replaced the sensor.

Swap it with the other downstream sensor, see if the code follows.

1998 GM procedure below…