Mine typically idles around 800 if the A/C compressor is on or if the electrical load is heavy. In mild weather, tends to drop to 800 at a stop, then after 15-20 seconds, goes on down to 600. 400 does seem too low.

Suggest to pull the engine codes. Many chain parts stores (AutoZone, etc) do this for free, or at least they used to. Any stored codes may give insight as to what is going on. All I can provide at this point is speculation on what it might be.

The fuel economy this time of year suffers due to the winter blend, but this is typically only about 1-2mpg - certainly nothing like you're experiencing.

If you haven't cleaned the MAF sensor and throttle butterfly - might be a good thing to try, just be sure to use the special MAF cleaner and do not force the butterfly open or closed. The two times I've done this to alleviate a surging problem, it helped.

Hopefully, others will be along shortly with their ideas. Good luck, and keep us posted.

 

This may sound simple stupid but try changing your air filter.

It's worth a shot to start basic and cheap before jumping to o2 sensors especially without a cel

Even if it looks alright iit can still be clogged enough to cause a problem.

Also like mentioned above clean the throttle body and maf sensor

 

Alright. I'll tackle those ideas first before going major. Will keep y'all posted.

 

ChvyMan, I'm glad you've been finding the community feedback helpful so far! I realize you're likely seeking DIY input, but I'm available if you would like any assistance working with your dealership towards a resolution. Please feel free to send me a private message through the forum anytime for further assistance!

Best,

Katie
Chevrolet Customer Service

 

I have an 08 ltz an changed the air filters my last oil check its was about $20. The thing is it helped the problem but didn't quite fix the problem so I'm going to try a whole flush system this time and maybe a tune as well.

 

Just wanted to give a bit of an update regarding this. I went for the expensive complete fuel injection system cleaning (the intravenous one), and replaced the air filter. While the car idles now around 800rpms, it still tends to fluctuate a bit. Not as much, so I think the advice given helped, but didn't completely solve the issue. I think the next step is a tune-up. Maybe better spark plugs and plug wires will be the cure.

 

I think the next step is a tune-up. Maybe better spark plugs and plug wires will be the cure.

If I've heard and read right, conventional wisdom suggests sticking with the OEM AC-Delco plugs. Changed mine at 88,000 miles only because I didn't believe the 100,000-mile claims - plugs looked great, gap had only opened up 0.001".

As for the wires, I'd be inclined at this point to also stick with the OEM stuff. Tried a set of AutoZone's Duralast wires on the '89 Ford - essentially a waste of money and time, IMO.