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View Full Version : Rough idle and bad MPG


Raudermaster
08-12-2006, 05:28 PM
Well, it's not terrible MPG, but I feel it should be better than what it is. When I'm in D and just idling, it feels like the car wants to shut off, then revvs back up, except the RPM gauge is fine, but to me that's what the car feels like. It's like, soft how it should feel, then gets all rough like it wants to stall. I mean, I still have a warranty on it, so I'm going to bring it back to the dealer and have them take a look at it. I think if there's something wrong, it will fix my MPG status. Anyone else experience this?
Drock96Marquis
08-12-2006, 08:39 PM
Slight misfire?
Sticky IAC? (wouldn't cause your bad MPG though)


Did you recently clean the engine?

Possible your plugs are fouled, gapped wrong, etc. This would effect idle smoothness and likely MPG some. But the low miles of your car make me think this would not be the cause.
usafsniper
08-13-2006, 02:18 AM
Well, it's not terrible MPG, but I feel it should be better than what it is. When I'm in D and just idling, it feels like the car wants to shut off, then revvs back up, except the RPM gauge is fine, but to me that's what the car feels like. It's like, soft how it should feel, then gets all rough like it wants to stall. I mean, I still have a warranty on it, so I'm going to bring it back to the dealer and have them take a look at it. I think if there's something wrong, it will fix my MPG status. Anyone else experience this?

Possibly an O2 sensor. Just had the exact problem with the wife's Trailblazer, only 15K miles. Stuttering idle, random surges at speed and drop in gas mileage. Tech picked it up on diagnostics immediately and it's back to normal now. Fairly inexpensive fix on your own. Good luck.
Raudermaster
08-13-2006, 06:19 PM
Have an apt. schedule at the dealer for this week sometime. Thanks for your help guys, I hope they fix it.
ckadiddle
08-14-2006, 08:22 AM
I also have an 03, recently had it in for regular maint stuff and mentioned that idle seemed to be getting rough. Service writer called me back to tell me that there was an "updated" part number spark plug that could be installed that would probably help. I authorized it, and she idles better now, and is noticeably stronger under heavy and WOT. That may have something to do with your issues.