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Help with unstable idle

daymdaym Member Posts: 1
edited July 2015 in GMC
Hello, so I have a 2003 envoy 4.2 v6 that is a solid workhorse she has 310k on it and has never gave me any issues at all. In fact apart for the regular maintenance the old girl has never left me standing or having to get the dreaded "PT" Public Transport. However......I just recently did a trip to New York and Philly and on the way down (from Toronto) I had a engine light come on and loss of power light came on and all of a sudden the car had restricted acceleration. I was lucky as I was pulling off the highway and in to a service station when this happened. After doing some research on my phone, and comparing the codes the car gave and ones online it turns out it was an issue with the Fan Clutch.
So I unplugged it and sure enough it pull back up to speed and had no issues in fact the car didn't over heat or cause any problems at all. Once back in Canada I did go buy a Fan clutch and installed it myself, again after looking through the Haynes manual and some online videos I figured I'll get a quote at a garage and decide if that would be easier as apparently I needed a specific tool. I got a quote of 3-4 hours and $110 an hour, so I though hmmmmmmm...after some thinking I decided to do it myself as i'm not a complete dummy when it comes to swapping things out.
I rented the tool, had my socket and spanner set and got to work.
I didn't do everything the videos said like remove the fan cowl that's attached to the top of the radiator and i still managed to make it work...but I think I messed something up with the idle pulley and Tensioner.
I started to turn the wrong bolt on the tension pulley as I noticed it was doing nothing so I started to turn it the other way but still nothing (I later found out it was turning the wrong part on the pulley) however I didn't stop there because I noticed nothing working so I thought I was doing the wrong part, so I started to mess with the idle pulley nut and after a few turns still nothing, so I gave up.
I ended up getting the fan clutch bolt loose and finally get the whole thing off and replacing it with the other one.

So I after clearing the codes and then leaving it running for a few minutes (5-8) no engine light and fan works perfect, BUT, I took it out for a test drive and noticed my rev's when idle seem to shift from 700 down to 400 and even sometimes completely cutting the car out. Just want to make it a point of saying I did disconnect the negative terminal when I did this so the computer should not have been effected.

can anyone give any advice on where to start to diagnose the problem. My first guess is turning the idle pulley nut a round the other way, but I really don't want to mess things up even worse.

Thanks to anyone in advance!!!


  • Options
    eliaselias Member Posts: 2,209
    engine may run a bit different after the battery disconnect because ECM is relearning - but it shouldn't stall, of course. It should relearn plenty after 15 minutes or halfhour of driving, I'd guess. Possibly consider that idler pulley/tensioner/belt is not to control/affect the idle-speed of the engine whatsoever. It's only to maintain proper belt tension/alignment.
    For idling issue with an older engine, one of the first things to consider to check or swap are the O2 sensors.
    A longer shot: Does idle smooth out if you remove the valve cover cap? Is the oil looking like milk chocolate or watery? Is coolant disappearing with no visible leak? (if yes/yes/yes, then an intake gasket may have failed.)
    Even if there is no check-engine/OBD light, have you scanned for new/pending OBD codes? What were those codes that you cleared - maybe they were a clue for the issue now? Another next thing to try to determine is whether the issue is with fuel or ignition. (In general I'm suggesting that there is another issue, something unrelated to the idler-pulley situation - sounds like you were quite diligent and comprehensive with that swap.)
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