1999 GMC Suburban Logo
Posted on Jul 17, 2011
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1999 GMC Suburban K1500 5.7L. When it is first cranked, doesn't matter if it is first crank of the day or the tenth, it will idle ok but when it is put in gear it studders and acts like it isn't getting enough fuel. After about 30 seconds, it runs and idles perfectly. This will happen each time I shut it off and it sits for a few minutes. I have good fuel pressure, new fuel filter, clean air filter, new MAF sensor(waste of money), ran Lucas injector cleaner through it several times and, like I said, it runs fine after 30 seconds. Any other ideas? It threw 0171 and 0174 codes but seems to throw the 0171 more often when I clear them. It was also doing this thing about six weeks ago where it would spin over in the morning for a long time before it would crank. Not doing that now but I believe it was humidity or moisture related and now that it is 100 degrees every day in Dallas without rain, it has not been a problem. Thanks, Chris

  • chrisdegnan Jul 18, 2011

    It is not having the hard start issue any longer. Just the initial rough idle and it does not make any difference whether it is cold or hot. It does it every time it is cranked. First 30 seconds is a rough idle and when put in gear, it will not move and acts as though it is starving for fuel. It does not shut off. Just a rough idle for 30 seconds and then it runs normally until I shut it off again and then the same exact scenario. Doesn't matter whether it is the first crank up or the tenth. It will happen each time it is started.

  • chrisdegnan Aug 16, 2011

    OK, I have fixed both issues. The first issue with it studdering for 30 seconds and then running fine each time I cranked it was a huge vacuum leak that was causing the computer to over compensate for how much air was going into the throttle body.

    The second issue with the moisture problem was just that. I took the ignition module off and cleaned the old di-electric grease off of it and wiped on a new coat to both sides of the plate and no more issues.

    So neither one of the multitude of suggestions by the mechanics on here were in the realm of being close to what was wrong and would have cost me hundreds and hundreds of dollars if I had followed their advise. Not really sure how to get my money back.

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Hello and welcome to FixYa!
It was good that you replaced the given parts though the MAF sensor should have helped a lot but it seems that it acts the same still. Have you replaced the spark plugs? Can be faulty, full of carbon or has big gaps and may need replacement.
If the problem still persists then I'll be suspecting the ECM. The ECM itself may be faulty that's why it's acting up on first start. It should just give you a high rpm on cold and must go down once warm. If you happen to know someone who has a spare ECM then you might want to consider a swap and observe how it goes.
Hope this helps and thank you for using FixYa! Have a good one!

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Thanks for choosing FixYa Chris and welcome. Since you already have tested fuel pressure and changed the MAF, I would suggest changing your oxygen sensors. This is why. If the fuel pressure is correct, then there shouldn't be a bad fuel injector or clogged filter. The MAF can cause this issue, but since it is new, you know it isn't. Since you have the hard start and the problem goes away after the vehicle warms up a little, it would appear that one of the oxygen sensors or all are defective. Isn't code 0171 for the O2 sensor? I believe so but I am not 100% sure.

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