1990 Burb idles rough, shudders under accel/highway-speed, wants to die after start

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by dattomcat89, Oct 11, 2012.

  1. dattomcat89

    dattomcat89 New Member

    Hello all. My first post; hoping I can get some assistance.

    I have a 1990 R1500 (yes it's a GMC) 350ci TBI Suburban with 218,250 miles that has started to act pretty bad as of late (unless otherwise noted, the problems I describe all popped up about 4 weeks ago).

    First off, I'd like to say I changed the fuel filter 3 weeks ago, and the fuel injectors were changed around the middle of August. I've inspected the air filter and it doesn't look dirty, although I honestly can't remember the last time it was changed; if I had to guess, I'd say over 4 years ago. The oil and oil filter were changed around the same time as the fuel injectors, at 217,000 miles. All of the vacuum hoses were replaced around 205,000 miles.

    Here are the problems:

    1) When I cold-start it, for a short while it just doesn't want to keep running. I have to gas it quite a bit to keep the engine from dying; when I do this, I can't just give it half throttle, or else it'll red-line line. So I have to switch between giving it half throttle to keep it from dying, then easing off for a short bit to keep the rpm's from going too high. After maybe 15 seconds of this, I can let off the throttle all the way and it'll idle fine. I'd also like to add that my father tried starting the engine, giving it no throttle, and letting it die. Directly after that, he started it again (again, with no throttle at all) and it idled pretty rough, but eventually smoothed out.

    A few months ago, before the injectors were replaced, this specific problem wouldn't happen if, before trying to crank, I turned the ignition on and allowed the the fuel pump to prime the rails; doing so would also cause the engine to turn over on the first crank (although I suspect this is just because the old leaky injectors constantly kept the engine primed). Allowing the fuel pump to prime the rails no longer seems to help; the engine still has to crank several times to start up, and obviously the other problem I've just described still occurs.

    2) There is a very distinct smell of gas if you stand outside while the Burb is running, and is especially strong after it's been started. Before, the smell was so strong that my fiance reported being able to smell it, inside, while we were driving. She said the inside smell has become either barely noticeable or not noticeable at all, since we changed the injectors, although the outside smell is still very noticeable. Also, this problem has occurred since we bought truck in 2005; long before it started running bad; so perhaps it's not related to the other problems I'm listing.

    3) The truck used to only shudder once or twice under acceleration from 0 MPH up to highway speed, and only as the engine was warming up after a cold-start. Now it does it still does that, but also once maybe every 20 miles once I've been cruising at highway speeds for a while. And by shudder I mean it feels as though, for a brief instant, the engine is going to die; it causes the entire truck to lurch back and stop accelerating, immediately after which, everything is fine for another 20 miles.

    4) Either a surge or rough idling (occasionally accompanied by stalling) can occur one to three different times I'm stopped during my first 20 minutes of driving after the Burb has warmed up after a cold start. By rough idling, I mean the Burb will idle fine for 3-4 seconds, the engine will come extremely close to stalling, then the engine will again idle fine for another 3-4 seconds, repeat, repeat. The surges can be pretty dramatic; yesterday, when one happened, I'm pretty sure that if I hadn't had my foot all the way on the brake, the Burb would have lunged forward. I've noticed that the rough idling mostly smooths out (but doesn't entirely stop) if I turn off the A/C.

    5) If 1) doesn't occur, then relatively high directly-after-cold-start idle (which has happened for maybe 5 years) occurs instead.

    As I said in the beginning, I replaced the fuel filter a week after these problems popped up; that seemed to make them better for about a day, after which they got worse.

    After looking around various forums last night, I came up with some possible causes (some of which I'm more sure about than others):
    -MAP Sensor



    -IACV (I unplugged the electric connector that connects to the IACV last night, and was able to knock some small flaky debris out of it, if that means anything)

    -Plugs (changed around 180,000 miles, at which time I noticed one of the old ones had what appeared to be rust on the head) and/or wires (changed at the same time); I'm resisting checking the wires as they are surprisingly hard to get off of the plugs, some of which are also hard to get to

    -O2 Sensor (not highly likely as I checked for error codes yesterday and the Burb didn't display any)

    -Distributor rotor (I dearly hope not as the last one was a nightmare-ish pain to remove)

    -Distributor cap (I remember cleaning some black greasy buildup off the cap's plugs' wires' metal contacts last year, after which the Burb ran better [this was before these problems started, although at the time the Burb was also idling rough and occasionally shuddering; much less frequent and severe than now, though]; I haven't yet checked to see if there's more)

    -Fuel pump (would definitely explain 3))

    -Coolant temp sensor (would explain 1), 2), and 5), but not 3) or 4))

    I can imagine some people would want to give me trouble for listing possible causes that are easy or somewhat to check, but not checking them before I created this post. I would have done that if I had several free hours but due to the number of classes I'm taking, I do not. I wanted to first list all the problems I've been experiencing because I hope that somebody with more experience than me could point me to a very likely cause so I don't have to waste time checking all the things that, while easy to check, aren't likely to be the source of the problem (who knows, though; you guys could tell me that it's definitely the plugs or it's definitely the air filter).

    Thanks in advance for any help you guys can provide!
  2. oldmanstruck

    oldmanstruck Rockstar 100 Posts

    in my 88, at one point it had trouble idling. It started out ok every time, cold or hot, but a few seconds later, it was like "oh, keep the gas, I am going to die..." and later time, keeping the gas wasn't help since the engine just ran rough. I too replaced the fuel filter (not the casue), check all the fuel line, and I gave up.

    took it to the dealer and they said Distributor is the cause so have it replaced for about $650. After that, strong and smooth again. Older model don't have much fuel pump issue compares to the later model.
    I also thought about coolant temp sensor but very unlikely. O2 Sensor, i wonder that's the casue for older sub and plugs? I have the same plugs for the last 12 years.

    In my case, it's just the distributor. I can do basic DIY so I just have the dealer took care this for me.
    Good luck
  3. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    I would take a good look at the egr.
  4. dattomcat89

    dattomcat89 New Member

    Alright, thanks guys. When I have some free times one of these next weekends I come back from school, I'll check the distributor cap and
    rotor (and clean the metal contacts) and check the EGR, which I just found out isn't that hard to get to. :yipi:

    Also, if it means anything, yesterday I wiggled the wire contact of the coolant temp sensor (to loosen up anything that may have build up on it) and also took off the entire air filter housing so the throttle body had lots of air. Then I tried to start the Burb. It fussed and ran rough for a few seconds, but did not die, and eventually smoothed out. Guess I'll replace the air filter too.

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