GMC Sonoma Surging/ Rough Idle

DJOEYD114

MEMBER
GMC SONOMA

Hey all, I have exhausted all ideas on this, maybe you guys can help.

I have a 1999 GMC Sonoma (2.2L Auto) that is my DD. It started surging a couple of weeks ago intermitently then got worse. I had to change the Altenator (it blew) and changed the fuel filter at the same time. It was running better for a week, then started again. I changed the fuel filter again, ran ok, then back to the same crap. Today I changed the fuel filter AGAIN and put in a new fuel pump ($320) and it still surges. I have also been throug the rear wiring, redid all the grounds. It starts out at Idle now usually idles at 900 rpm but it will kick up to about 1300 without warning and when it does it revs up and down rapidly. It has in the past kicked down so low as to almost stall it, but hasnt since I replaced the fuel pump (could be since I only drove it for an hour). I am not getting any error codes so I am totally dumb founded. Any ideas?

Thanks

2 Replies

JEFFC005

MEMBER
1 POST

. The only difference between your truck and mine is two years (2001) and that I have a 5-speed manual. I had the surging idle that typically went between 700 and 1300 rpm. I took it to the shop and they reflashed the computer and it worked for about a week. Turns out the problem was a broken throttle position sensor - my laymans understanding is that the contacts were worn out in the idle area and that is why it didn't show up under driving. I'm not sure this is the problem you're having, but mine has been trouble free for about two years now. It cost around $180 to get it fixed at the local procare.