Doesn't Want To Idle

mjlimo82 · March 5, 2010

I have a '90 Sierra 4x4 with a 350 and 700R4... yesterday when I left work it started up fine and did good until about 3 miles down the road when I had to stop for traffic. Started to take off again, hit the gas, and it sputtered and hesitated, then went. It kept doing this all afternoon and by the time I got home it would barely even run at idle. This morning I went to start it up and it did the same thing - the only way it will start and run is if you give it gas like you would a carburetor. It seems to do fine if you keep your foot in it but as soon as you let off and it idles down, it starts bucking/shaking and then dies. I don't even know where to begin with this as this is my first TBI GM vehicle. I was thinking vacuum but I'm not so sure about that... I have access to a scanner if I need one but there's no lights on at this point. Can anyone point me in the right direction????

jrod332 · March 5, 2010

maybe a fuel filter.

mjlimo82 · March 6, 2010

I went ahead and bought a fuel filter because it probably needs one, but it threw a code earlier while I was driving it in an attempt to diagnose the problem. Going to get that checked tomorrow sometime... it runs fine out on the road but it absolutely refuses to idle no matter what you do. Stoplights/signs aren't fun - two footed driving skills must be fine tuned! When I got home from work this afternoon and it had sat all day (I drove the Dodge to work) it didn't want to start again; got it started and let it run for a few minutes and at one point it began running fine, but quickly went back downhill for no reason. Hopefully the code will give me a tip. It's difficult to diagnose because the truck has a dead cylinder anyway so a constant miss is always there... now it hesitates on top of that so you can just imagine how great it runs now. But again, out on the road going 25 or 55 mph it runs fine. (??)

mcreyaufmiller · March 7, 2010

I would try to clean the throttle body first. You can get cleaner from the auto parts store, use an old tooth brush and the cleaner, do not be afraid about how much you throw down the body, clean all around the blade, top and bottom and the body itself. This woudl be a good start. If you feel really adventrous, take the throttle body off and clean it on the bench. There are a lot of vacuum holes and also a fuel pressure regulator spring that breaks eaisly.

mjlimo82 · March 7, 2010

OK thanks. Cleaned the TB yesterday but I might take it off and clean it too. All of the vacuum lines "looked" OK but I didn't test them when I was messing with it. I'll have to check that spring out as well. It sets a code (or at least turns on the SES light on) but after you shut it down it goes off and who knows when it'll come back on after that. I've only seen it come on twice so far, so here's hopes that it will come back on again so I can get the scan tool to tell me what it says and go from there.

mjlimo82 · March 8, 2010

Well... it stopped doing it. I don't know why, but it mysteriously decided to run right - I did absolutely nothing to it (due to lack of time)! No complaints there for sure, but thought I'd let everyone know. Thanks everybody for all of your help!

Mike G · March 8, 2010

When mine didn't idle any longer, turned out to be a toasted distributor.... Also, I was having similar issues with a bad ground up front by the battery. You may want to check all your ground connections.

--Mike