Regular "miss" in idle after UIM/LIM job - Page 2 - 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 08-20-2007, 04:14 PM   #11
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Did you replace the spark plugs after the UIM was fixed? Coolant on plugs oould have affected one permanently.
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Old 08-20-2007, 06:10 PM   #12
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Default PCv

Sound like a vacuum leak. Check if your PCV is seated has the O-ring and spring installed.
Also I didn't notice if you changed your oil (its a long read).
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Old 08-20-2007, 11:23 PM   #13
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Quote:
Originally Posted by BillBoost37
I'm not sure it'* the MAF. It appears from your description that unplugging is defaulting you to higher rpms and smoothing the problem.

How old would you say the plug wires are? All are on and hooked up tightly? The #6 isn't touching the O2 wiring correct? Also.. have you pulled and checked all the plugs. It'* possible one is causing an issue.

My other thought was ...vacuum. Did you get all the vacuum connections back on and none are leaking? The U bend at the TB is a very common place for the line to split and cause issues.
On you first point, looking back at what I wrote, I see that I did not say that the idle returned to 1000 rpm after disconnecting the MAF. So, while I agree that the computer defaulted the missing MAF'* info, I am certain that the smoothness of the idle was real. I can hear the lack of a "miss"; I can feel the vibration while sitting in the car, especially when in gear; I can see the lack of the tach pointer dipping; and I can see that the serpentine belt tensioner is not bouncing.

The plug wires look almost new. They are all on and tight. The O2 wiring is clear. I have no pulled and checked the plugs because I believe that the "miss" truly disappeared when I pulled the MAF sensor connector.

To your third point, I'd say I believe I did get all the vacuum connections replaced. I'm not sure I know how to check for leaking, but the connections to the fuel pressure regulator, the throttle body (2) and the UIM (2 on a fitting that snapped into the UIM) are the only ones I am aware of. Did I miss any?

There is a hissing sound coming from underneath the TB where it mates to the UIM (I put a piece of vac hose to my ear and probed the area). But I don't know if it'* normal. All three of the TB nuts are equally tight, judging by the number of threads showing. However, one of the two long bolts holding the UIM down (the one closest to the EGR) is more like a stud with a nut frozen about 1.5 in down from the top of the stud. Again, I don't know if that'* normal, but I didn't have a deep socket that would fit it (9 mm, I think), so I cranked it down with an open-end wrench as best I could to match the torque spec.

I have more to say, but I'm thinking I should spread it around a little so there'* not too much in one post.
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Old 08-21-2007, 12:00 AM   #14
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Did you check the PCV valve?
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Old 08-21-2007, 12:04 AM   #15
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Quote:
Originally Posted by Bob Dillon
Sorry to sound like a broken record in this forum, but check all around for vacuum leaks.
What'* the best way to do that checking, Bob? I ended up hooking up an old vacuum/compression tester in the line where it goes...I don't know, to some kind of transmission switch? There was a badly degraded piece of hose there connecting two ends of hard line, so I replaced it and tee'd in the vac tester. The car was cold, but before I started it I removed the MAF and used CRC MAF cleaner and sprayed it down pjretty good and replaced it. I didn't let it die when I first started it; and it finally leveled out around 1000 rpm and pretty steady, though the engine speed would kind of float, its response lagging my input at the gas pedal. The vac tester read just in the grean, about 18-19 Hg/mm (I think those were the units). As the engine warmed up a little I could see the vac drop to about 16. I'm checking stuff all over the place and noticing how the whole "missing" business doesn't seem as bad since I cleaned the MAF, but still noticeable. The engine'* getting warmer and I look at the vac and it'* oscillating very rapidly from about 10 to 16 contantly, not rhythmically. What is that?

I pulled the connector to the IAC and there was no effect. So I shut down, removed the IAC. It was very hard to move the plunger, so I sprayed it down with TB cleaner and worked the plunger in and out a little. But I ended up pulling it out so I sprayed it some more and put it back together. It was a lot easier to move in and out but still pretty stiff. Is it supposed to be that way? I reinstalled it in the TB and started the engine. Idle was steadier and smoother than before; but the most remarkable thing was that engine speed followed my foot on the gas pedal much more closely, even normally, I'd say.

One thing I wanted to say to BillBoost'* question was that the two vac connections to the TB are not in great shape, but I'm having a real hard time finding replacements. A Pontiac dealership nearby had the same difficulty locating the part in their system as I did trying to find it in my FSM--except they finally found something. But it doesn't look like my setup at the TB. When you say "U bend" what do you mean? Both of my TB connections are "L" shaped boots. They seem to fit faily snuggly, but I will order the part, or assembly that they found, to see if it can fit.

There'* a new wrinkle I've noticed: I've had the engine heated up real good three times now since finishing the UIM/LIM job and only the second time did the larger, driver side, radator fan come on. The other two times neither fan came on, and both those times I could see a light vapor rising from the area of the top of the radiator. It kind of looks like coolant vapor, but smells like hot plastic. And I can not identify any leaking whatsoever.


I've noticed improvements related to both the MAF and the IAC. I'm wondering about the O2 now. I think I'll have to try to find a scanner.
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Old 08-21-2007, 12:09 AM   #16
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Quote:
Originally Posted by imidazol
Did you replace the spark plugs after the UIM was fixed? Coolant on plugs oould have affected one permanently.
I replaced all the plugs with new ones when I fired it up for 15 seconds with coolant drained and the coolant cranked out of the plugless cylinders (and then let dry that way for a day) just before fixing the UIM. Do you still think there could be a damaged plug issue?
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Old 08-21-2007, 12:15 AM   #17
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Default Re: PCv

Quote:
Originally Posted by SSEBONNE4EVA
Sound like a vacuum leak. Check if your PCV is seated has the O-ring and spring installed.
Also I didn't notice if you changed your oil (its a long read).
Sorry about the length. I'm trying to convey as much info as I can without fluff--but I'm very observant!

My PCV situation has 2 O-rings and no spring. In fact, I had to reuse the cap from the old UIM because the new one that came from APN was the wrong type, in that it was open, like it was expected that I'd have something fit in the top to close it off....I don't understand how it'* supposed to work, since there is no connection to anything. The PCV just sits there under the cap!

Yes, I changed the oil early on, soon after I discovered the hydrolock condition.
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Old 08-21-2007, 12:17 AM   #18
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Here is the setup you should have -

Name:  95L36PCV.jpg
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Old 08-21-2007, 12:19 AM   #19
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Quote:
Originally Posted by Technical Ted
Did you check the PCV valve?
I used the old one, since it seemed to rattle nicely. The fit was snug beneath the cap. I haven't re-checked it since installing the new UIM. How would you suggest to test it, Ted? I'll do it, if you say how. Thanks.

Thank-you, everyone.
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Old 08-21-2007, 12:26 AM   #20
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Quote:
Originally Posted by Bonneville92V688
Here is the setup you should have -

Yes, sir, that is exactly what I have! But what APN sent me had an open top,with some kind of plastic bracketing, like I should have something to attach to it to seal it off. Your pic is exactly what I have installed right now.

I may be over thinking this a bit, but, if APN sent me the wrong type of cap for my PCV, could they have also sent me...something else that was wrong for my application? Naaaa...there was no mention of any alternatives on their website--at least nothing that caught my eye.

Thanks for the clarification.
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