Stumble at hot idle, stalling
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Northstar Engines and System Technical Discussion Discussion, Stumble at hot idle, stalling in Cadillac Engine Technical Discussion; My 97sts has an iussue with stalling once in a while, and when hot has a "stumble". It's like a ...
  1. #1
    davz's Avatar
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    Stumble at hot idle, stalling

    My 97sts has an iussue with stalling once in a while, and when hot has a "stumble". It's like a miss, but no codes. Once in a while, I get the p1599 code - stall or near stall. I used to get the p0171 and p0174 codes for lean banks, but they don't seem to be coming back.

    I did get a p0441 code the other day. Something with the EVAP system.

    Should I clean the TB and IAC?

    I did use a bosch oxygen sensor for the precat, but this started about 500 miles after that.

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    Re: Stumble at hot idle, stalling

    Can't hurt to clean the TB. It should be done on a regular basis anyway. Check for vacuum leaks. Check the manifold mounting bolts to be sure they are not loose. Bosch parts don't seem to play well with Northstars. Hard to say if that is the culprit or not, but I wouldn't use them.

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    davz's Avatar
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    Re: Stumble at hot idle, stalling

    I wiped out the TB when I had the intake off for the HG job, but I didn't use any carb cleaner.

    I will clean everything in the morning.

    I did check for vacuum leaks. Can't find anything.

    There is a EVAP? component on the rear cam cover that has a port on it with an open end. Is this supposed to be open?? Even with the engine out, I couldn't find a vacuum line that would go to it. It's actually got a rubber elbow on it with no line. What the hell is that thing?

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    Submariner409's Avatar
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    Re: Stumble at hot idle, stalling

    Depending on your setup, that's the vacuum side of the PCV system......the PCV valve (maybe an orifice) fits in a rubber grommet in that hole, and a plastic hose with rubber connectors goes from the valve nipple to another fitting in the end of the intake manifold, sort of behind the p/s pump. The clean air supply comes from the outside of the TB (before the butterfly) to the corresponding hole in the front cam cover, driver's end.

    Without the PCV hooked up to the intake manifold, you have a big vacuum leak, OR someone has blocked off the manifold nipple, changing the air/fuel ratios. There's your problem.

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    Re: Stumble at hot idle, stalling

    There is a EVAP? component on the rear cam cover that has a port on it with an open end. Is this supposed to be open?? Even with the engine out, I couldn't find a vacuum line that would go to it. It's actually got a rubber elbow on it with no line. What the hell is that thing?
    I think that is the vent. It's supposed to be open.

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    Re: Stumble at hot idle, stalling

    Ranger is right- that rubber elbow is a vent. It can fool you at first as something that's disconnected. Have you checked fuel pressure? Does it start good/run good when cold?

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    Re: Stumble at hot idle, stalling

    Ok, I had blocked off the "vent" that may have something to do with the problem. I am going out right now to clean the IAC, EGR, and TB.

    It does run good when cold and starts up real good. I may have to get a fuel pressure guage. I did replace the regulator about 2 months ago, but maybe I'm suffering from a weak fuel pump. A couple of weeks ago, I was getting onto the expressway, and there was a flutter at high RPMs (WOT) like it was too lean. Thats when I got the p0171 and p0174 codes. That condition seemed to go away by itself. My gas guage intermittently works, so maybe there's a bad ground back there.

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    Re: Stumble at hot idle, stalling

    A couple of weeks ago, I was getting onto the expressway, and there was a flutter at high RPMs (WOT) like it was too lean. Thats when I got the p0171 and p0174 codes.
    Have you checked the plenum for a vacuum leak?

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    Re: Stumble at hot idle, stalling

    My car is a 97. I don't think I have the plenum like the newer cars.

    I cleaned the TB, IAC, made sure the intake bolts were tight, and really checked for loose wires, etc.

    Drove it and it still does the stumble.

    It only does it at idle from what I can tell. It's like the engine temporarily stops for like a nanosecond. Sometimes when it does it, the tach moves a little. Its like a thud and you can feel it in the whole car. It's not rythmic. Its random. I drove 15-20 miles and have no codes. And it didn't stall this time at all.

    Man this sucks. The only thing I can think of is crank position sensors. Another thing that is stumping me. There is 3 ports on the EVAP switch. 1 has a vacuum line on it, 1 has the elbow with no line, and 1 (the rear facing one) has nothing. If that is supposed to be a vacuum line, where does it go to?

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    Re: Stumble at hot idle, stalling

    Davz, if you don't have a fuel pressure guage, what you can do is using a tire tool, screw the valve out of the end of the fuel rail (make very sure the key is off) and use a piece of 3/8" fuel hose and a couple of good clamps, attatch the other end to any type of air pressure guage. There's a cheap temporary fuel pressure guage. It works.

    The EGR valve can sometimes get deposits stuck in it and believe me, Northstars need their EGR valves to work right. I don't know if you mentioned that on this thread yet or not but if you haven't checked it, it can't hurt. It's cheap and easy (2 bolts). You can also start the engine up without it for a few seconds and it will blow any loose carbon out. Use some carb cleaner and compressed air and blow it out, work it back and forth to free it up.

    It's hard to figure out what that stumble could be- it's random, and only when warm.

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    Re: Stumble at hot idle, stalling

    Your 97 should still have a plenum, its the black thing just under the N* cover....

    Here's a link with removal and install instructions complete with pictures

    http://www.cadillacforums.com/forums...um-issues.html

    The guy that posted this write-up says that his car kicked P0171 P0174 as well, so cracked plenum is most likely the problem...

    Post back and let us know!

  13. #12
    penguin7 is offline Cadillac Owners Member
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    Re: Stumble at hot idle, stalling

    My 98 deville had a similar problem. Would stumble on idle and even stall sometimes. Took awhile but we found the problem to be a vaccum line was having a small leak. Don't know which one but the leak was on the under side of the engine. No stalls and runs like a top

  14. #13
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    Re: Stumble at hot idle, stalling

    Sounds like I will have to remove the intake and reseal or replace the gaskets. And no, I dont have the "plenum". The TB is bolted right to the intake.

    I still have to check the EGR. My wife drives the car to work and doesn't get home till late, so I will do it as soon as I can.

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