Regular "miss" in idle after UIM/LIM job - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-21-2007, 10:07 AM   #21
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Quote:
Originally Posted by Must_Wrench
There is a hissing sound coming from underneath the TB where it mates to the UIM
It'* a process of elimination. You recently changed your gaskets When removing the LIM, remember that EGR pipe that was under the TB and bolts to the LIM. Those are prone to cracking at the edge where it is held to the LIM by the piece of metal. Currently I'd say if you hear a leak in that area..this is a major suspect.

The easiest way to test for vacuum leaks is with a can of TB or carb cleaner. Use the straw that comes with it to aim the spray at each vacuum connection. Any change in idle while you spray is where a problem exists.

Be careful around the exhaust.
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Old 08-21-2007, 11:00 AM   #22
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The open pcv housing cap you received in the APN kit is for newer cars equipped with MAP sensors. I think GM started adding the MAP sensor in '97. If your car doesn't have a MAP sensor, you just re-use your old cap as you did. APN should mention this in their instructions.
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Old 08-21-2007, 11:39 AM   #23
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Must_Wrench:

I have a similar problem, but worse, problem (after UIM LIM replacement) and have not found the solution yet. I seem to have a higher idle, and am also having trouble starting without pressing on the gas pedal. The missing is frequent, but not perfectly regular. It seems to be more of a miss due to electronics rather than plugs/wires. At higher RPMs the engine runs very well. I am also wondering about the MAF, since there was coolant in the TB, though MAF wires looked okay. But I was also thinking it might be more related to the CPS. Though the check engine light bulb works, it has never come on while the car was running for me.

My PCV setup looked the same, but I don't remember having the o-rings around it. It fit very snugly into the manifold. I'll check that again.

here is my post:
http://www.bonnevilleclub.com/forum/...ic.php?t=83897

I think I will try the MAF disconnect as well.

Ken
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Old 08-21-2007, 11:53 AM   #24
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Ken...there'* been a post in your thread. Both of these sound to be vacuum related.
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Old 08-21-2007, 09:59 PM   #25
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Quote:
Originally Posted by BillBoost37
Quote:
Originally Posted by Must_Wrench
There is a hissing sound coming from underneath the TB where it mates to the UIM
It'* a process of elimination. You recently changed your gaskets When removing the LIM, remember that EGR pipe that was under the TB and bolts to the LIM. Those are prone to cracking at the edge where it is held to the LIM by the piece of metal. Currently I'd say if you hear a leak in that area..this is a major suspect.

The easiest way to test for vacuum leaks is with a can of TB or carb cleaner. Use the straw that comes with it to aim the spray at each vacuum connection. Any change in idle while you spray is where a problem exists.

Be careful around the exhaust.
I think that got it, BillBoost! There was a big effect spraying around at the base of the TB and especially a little lower where the EGR pipe enters the LIM, and no effect anywhere else, even on top of the TB where it mates to the UIM. I've already begun to tear it down, but things are a bit hot and I'll have to wait until after work tomorrow to finish taking the UIM off and, hopefully getting it back on.

Now what am I looking for? Did you mean to say that the EGR pipe itself is prone to cracking where it enters the LIM? I remember thinking at the time that the EGR pipe retention mechanism, at the LIM, seemed kind of iffy. The hole in the LIM where the EGR pipe entered was quite a bit larger than the EGR pipe, and I didn't notice any flaring on the pipe end. It looked like the only thing keeping it in was the thick black plastic egg-shaped gasket/cover that bolted onto the LIM with a single bolt. It seemed all of the sealing was supposed to happen at the mating surface of the LIM and the gasket/cover, and by friction between the pipe and the hole in the gasket/cover.

I'm thinking that the real issue is at the UIM-gasket-LIM junction near the TB, since spraying at that front right corner got a pretty big effect. This brings me to the one part of the job that dissatisfied me when I was doing it, and I should have known better than to let it slide. The gasket fit somewhat poorly to the square openings in the UIM--a slight misregistration, so to speak. I figured the tolerances didn't need to be too tight and that as long those plastic locators were in their holes everything would settle correctly when I torqued it down. There are some clips on the UIM that hold the gasket to it, so, even though the directions said to place the gasket down on the LIM and then drop the UIM on top, I figured I could avoid having to deal with the plastic tube that goes to the PCV valve by just assembling the gasket to the UIM and lowering the whole thing to the LIM. I'm wondering now if that isn't the source of my problem. What do you think?

Maybe cleaning the MAF and IAC did a lot of good because when I first started the engine with no gas applied it didn't want to die at all. And there was no hissing and the vacuum was good on the tester gage. After a few minutes, though, all at about the same time, the "missing" started and the hissing started and the tester gage started fluttering...but that'* also about the time when the computer starts to pay attention to its sensor inputs, so I'm not completely sold on the vacuum problem being the complete solution. But, first things first, eh?

Can you offer any clues as to what to look for, precisely, as I take the top of the engine apart? Thanks.
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Old 08-21-2007, 10:04 PM   #26
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Quote:
Originally Posted by bill buttermore
The open pcv housing cap you received in the APN kit is for newer cars equipped with MAP sensors. I think GM started adding the MAP sensor in '97. If your car doesn't have a MAP sensor, you just re-use your old cap as you did. APN should mention this in their instructions.
I was confused for a few minutes, wondering if I even got the right kit. But I decided that cap just was obviously NOT going to work.
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Old 08-21-2007, 10:07 PM   #27
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Quote:
Originally Posted by rockken_cosworth
Must_Wrench:

I have a similar problem, but worse, problem (after UIM LIM replacement) and have not found the solution yet. I seem to have a higher idle, and am also having trouble starting without pressing on the gas pedal. The missing is frequent, but not perfectly regular. It seems to be more of a miss due to electronics rather than plugs/wires. At higher RPMs the engine runs very well. I am also wondering about the MAF, since there was coolant in the TB, though MAF wires looked okay. But I was also thinking it might be more related to the CPS. Though the check engine light bulb works, it has never come on while the car was running for me.

My PCV setup looked the same, but I don't remember having the o-rings around it. It fit very snugly into the manifold. I'll check that again.

here is my post:
http://www.bonnevilleclub.com/forum/...ic.php?t=83897

I think I will try the MAF disconnect as well.

Ken
Thanks for the link, Ken. Our situations appear to be very similar, but with a couple of significant differences. I intend to keep posting to this thread until the matter is resolved. Hopefully my solution can serve you as well.
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Old 08-21-2007, 10:41 PM   #28
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As you will see from my thread, I seemed to have missed that lower PCV o-ring.
Things are much better, but I would not say perfect.

As for the EGR tube, I thought that the LIM side of the tube had a small raised portion, which fit into the hole of the LIM. The "clamp" block is supposed to be loose around the tube, so that it just holds the flat part of the tube sealed against the LIM. That said, I will be checking mine tomorrow as well.

Good Luck!

Ken
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Old 08-21-2007, 11:27 PM   #29
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Stop tearing it down!!!

All you need to do is use a 13mm wrench to get the tube from the egr to lim off. Nuts on both ...wiggle pipe out and you'll see a crack in it near the lim. New tube time or holler if the dealer thinks you should take out a mortgage for one. I've got a few used in good condition spares here.
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Old 08-22-2007, 10:32 AM   #30
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about your PCV system...


The bottom, underneath the PCV valve, is open to the crankcase, sealed to the UIM manifold by the bottom o-ring. Though the top of the PCV valve sits in the cap, it is not blocked off (blow thorugh the bottom to see). on the intake manifold side (drivers side) of the PCV area opening, you should be able to see the end of the vent pipe (white plastic), where it comes up from the center of the intake manifold.

Ken
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