rough idle and poor fuel milage after tune up


Asked by Dec 21, 2011 at 08:45 PM about the 1994 Geo Tracker

Question type: Maintenance & Repair

i changed the air filter, fuel filter, plugs and wires a little after i bought my geo tracker and i was getting 29 to 31 mpg. now after the tune up a check engine light came on and only gets 24 mpg top and has a rough idle. i changed the o2 sensor thinking it was bad but not the answer. a guy flashed the CEL and it came up rich/ lean either air or fuel dont remember what the book read. what can i check next?

7 Answers


If you didn't gap your plugs you could have one gapped wrong and it will idle rough. Or you might check the wires to make sure one didn't get crossed.

2 of 2 people found this helpful.

Hi. Remove Left Dash Speaker Cover. Locate The Small Switch Behind Speaker, Move The Switch To The Other Side (SLIDE IT OVER) The Will Take Your GEO OFF Of The Nonadjusting Vairables. On GEO Trackers If The Check Engine Light Comes On The Car Goz Into POOP Mode. Flip The Switch, Now Proper Timming,,O2..ETC Will Be Working FULLY Again

11 of 11 people found this helpful.

i gapped the plugs correctly and i did try to flip that switch. when i installed my radio i noticed that switch and didnt know what it was and i tried switching it and nothing happened. that was when no CEL was on. but i did some forum searches and switched it when it came on. i tried driving it with it switched to where it is off and i tried switching it back but it comes on like a light switch. didnt do that before there was a problem. is the switch like a reset swotch or does it trip like a breaker? thanks for all the help

3 of 3 people found this helpful.

check the order of your spark plug wires make sure you have not miswired your engine. The rough idle is being caused by a miss which will cause your car to not burn fuel in one or more clynders sending your exhaust gasses out of spec. This causes your check engine light to come on and point to your O2 sensor. Check to make sure your spark plug wires are going to the correct clynder. You will find that everything will return to normal.

1 of 1 people found this helpful.

ok thanks will check it out and make sure

I Would Like To Know If You Figured It Out With The Geo Bc Mine Is Doing The Same Thing


Mine also is running rough, but after it warms up for about 30 min, then it runs great, what could be making this happen, somebody told me the egr valve was bad, and on that switch, which way is the switch suppost to be?

3 of 3 people found this helpful.

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