Runs rough.

Seth Deen

Asked by Nov 09, 2014 at 07:16 AM about the 1991 GMC Sonoma

Question type: Maintenance & Repair

It idles fine, but when I get into third
or more, or if I'm idling in second, it
runs really rough.But when the
service engine soon light comes on, it
runs fine. what's wrong? please help

2 Answers


you will have to read that engine code. sounds like the computer is trying to compensate for something. Google "how to read OBD1 codes with a paper clip" you will get a simple procedure for reading the code.

1 out of 1 people think this is helpful.

mine wasn't that old sounds like o2 sensor or emission problem go to and auto parts that will read your codes for free parts. for your truck are fairly cheap so even if you have to replace a couple of sensors it won't cost a arm &a leg .iban

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