Rough idle / Engine Dying and Low Oil Pressure Warning

[StormPursuit]

2005 TB LT I6 4.7, Built January 2005

I've been looking at different threads and been asking some friends and I can't seem to figure out how to fix this issue. My engine runs really rough when at idle (Drive Gear) for example when sitting at red lights, etc. In park it's not quite so bad. The engine will then idle real low, and shut off with the low oil pressure light coming on as the engine shuts off. The light is coming on (my guess is because it idles so low that the engine isn't pushing the pressure so it kicks the light on). What our conclusion has come to, is that with my Trailblazer having 132k miles on it that the Mass Air Flow sensor may have some debris and need cleaning. I cleaned the throttle body and it's back to new. The engine still runs rough. I looked and looked for the MAF sensor and found through this forum that my model (early 2005, january) wasn't produced with a mass airflow sensor. So now I'm thinking maybe the cause of the rough idle and engine dieing would be the MAP? Does anyone have any suggestions on what the issue might be. Where is the MAP on this truck? You folks on this forum have been amazing in the past.. and even helped me win a lawsuit against a shady mechanic shop. So, I know someone will help me figure this out!!

Thanks a bunch!

 

[CaptainXL]

Does it run ok and smooth out if you drive it or increase the rpm's?

 

[StormPursuit]

Does it run ok and smooth out if you drive it or increase the rpm's?

Yes, when I'm driving at speed it smooths out. If I'm coasting at speed I notice it idles smoother.

 

[CaptainXL]

Yes, when I'm driving at speed it smooths out. If I'm coasting at speed I notice it idles smoother.

Since good fuel pressure and spark are needed to maintain rpm's at speed then I would suspect a vacuum leak more than likely. Our intake manifold being loose is a common issue. I would not waste any time checking anything else but this. Here is some more info. Read the section entitled "rough idle and stall" and "findingvacuum leaks". See if that has any similarities to what you are experiencing.

Random-Misfire Page

 

[CaptainXL]

I have a huge suspicion that many throttle/air related issues people get after replacing the battery (or for whatever reason disconnecting the battery) is due to idle relearn done by the pcm. My theory is quite simple and is actually based upon work done by Scanner Danner since I have studied his work done on vehicles involving short term and long term fuel trim. Basically as the vehicle ages the pcm accomodates small incremental changes in idle fuel and air mixture. When a small enough vacuum leak is happening the pcm will correct the idle a small amount. Over a period of months and years the vacuum leak can become so big that other codes may or may not be triggered. But usually the home mechanic doesnt know of a leak until cleaning the throttle. This and disconnecting the battery give the effect of the pcm starting over new with its default air/fuel ratio and throttle angles. Since the throttle is closed more due to a vacuum leak (that may be getting worse) the idle is maintained correctly. But when the pcm learned values are erased such as in a battery disconnect the vehicle will idle poorly or stall all together because the pcm is starting over new and allowing too much air into the engine. Really the only way to solve this is to find and correct the source of the vacuum leak. I guess this really isnt my theory at all. It happens with a lot of vehicles. Just thought I would reiterate with respect to how our vehicles behave.

 

[StormPursuit]

Awesome. I hope looking into this fixes the issue. Between this, and the brakes squeeling constantly after both rotor and brake replacement, proper lubing.. My wife is starting to hate this car. she's looking at new explorers and I'm thinking the TB might not stay in the family much longer. Plus the engine shutting off randomly is becoming a safety issue. I hope I can get this fixed without going to a shop or stealership.

 

[CaptainXL]

Awesome. I hope looking into this fixes the issue. Between this, and the brakes squeeling constantly after both rotor and brake replacement, proper lubing.. My wife is starting to hate this car. she's looking at new explorers and I'm thinking the TB might not stay in the family much longer. Plus the engine shutting off randomly is becoming a safety issue. I hope I can get this fixed without going to a shop or stealership.

Think about what you said. If you can afford a new vehicle then surely you can afford to take it in to get it fixed. Or even better fix it yourself with our help. The reason we fix vehicles ourselves is so we can use the money on other things. Definitely not $500+ per month new car payments! I think you need to sit down with your wife and calculate this out. A new car is many things but a money saver it is not. The issues you list here are definitely not major in any way. They are all known issues that many 2005 Envoys have. Very fixable.

 

[StormPursuit]

Think about what you said. If you can afford a new vehicle then surely you can afford to take it in to get it fixed. Or even better fix it yourself with our help. The reason we fix vehicles ourselves is so we can use the money on other things. Definitely not $500+ per month new car payments! I think you need to sit down with your wife and calculate this out. A new car is many things but a money saver it is not. The issues you list here are definitely not major in any way. They are all known issues that many 2005 Envoys have. Very fixable.

 

[Canary2323]

I had same issues pulled out maf sensor cleaned it and reset pcm and started up no problem. Great 7$ fix, hope this works for you.

 

[CaptainXL]

I had same issues pulled out maf sensor cleaned it and reset pcm and started up no problem. Great 7$ fix, hope this works for you.

There is no MAF sensor on 2002-2005 models.

 

[Canary2323]

Damn OK, my an 06.

 

[CaptainXL]

Even if you did clean the MAF sensor and got it working again that wouldn't rule out any vacuum leaks. There is plenty of evidence from other members that they attempted to clean or even replace the MAF and ended up getting lean and or misfire codes. So check that vacuum and tightness of the intake manifold bolts.