97 97 Bonneville rough idle after start then runs fine. - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-30-2011, 11:03 AM   #1
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Default 97 97 Bonneville rough idle after start then runs fine.

Hi everybody,
First post on this board maybe you can help me out.

So a little history of the problem. Car was becoming hard to start, it would start up then idle rough,sometimes it would stall out and sometimes it would catch and run just fine. About 2 months ago during a bad snowstorm, was stuck in traffic for 2hr or so and car started to idle rough then stalled out. Would crank just fine then it would try to start but would just fall on its face. Let it sit for an hour and it started up and ran great. Couldn't repeat the problem until I discounted the battery and I ran into an air mix actuator problem.(thanks to this forum I have rigged it until summer) I was trying to re-learn the actuator and by doing this I was doing a lot of starting and short trips, during this process I let the car idle awhile and I started to get the rough running symptom, I shut the car off and couldn’t get it to re start until the next morning. (The same symptoms where present as described above) I did however get a Bank 1 lean code. Now the car will start fine sometimes and other times it will start and does not want to idle. It seems to be searching for the idle but when it finds it it surges to 2krpm then drops down and idles normal and runs great. I have noticed that if I do a short crank and it doesn’t start than the problem will occur, if I give it a long crank then it will start normal most of the time. The SES light went off after the required 3 cycles and has not returned.

I have changed the IAC, plug wires,and fuel filter. About 6 mouths ago the UIM failed, so I changed the UIM,lower gaskets,plugs and cleaned the TB.

Any help will be appreciated.

Thanks
Matt
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Old 01-30-2011, 03:34 PM   #2
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Sounds like a crank position senor to me or even a bad coil
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Old 01-30-2011, 03:51 PM   #3
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Try unplugging the MAF and see if things change.
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Old 02-03-2011, 06:51 PM   #4
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Checked the coils and I am getting
5.6K ohms
5.6K ohms
4.8K ohms
when the car is cold and about another 1K after they warm up.

Checked fuel pressure and the gauge is reading around 30 psi. I know that is low. I changed the filter about a 2 weeks ago. Can the fuel pressure regulator cause this? I took the line off and the pressure increased maybe 2psi.

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Old 02-03-2011, 06:52 PM   #5
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I also unplugged the MAF and not much changed.

Matt
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Old 02-03-2011, 06:59 PM   #6
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Personally, I would not be happy with those coil readings. I like them to be even.

If the fuel pressure really didn't change when you unhooked the FPR vacuum line, then your fuel pump is going out. And that will cause all kinds of problems.
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Old 02-03-2011, 07:05 PM   #7
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Car runs great when you get it started. Can the fuel pump still be to blame. I have done WOT and there is no hesitation or anything like that.

Thanks for your help
Matt
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Old 02-03-2011, 07:08 PM   #8
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Also vacuum line to the fuel pressure regulator has a very slight hint of gas.
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Old 02-03-2011, 07:12 PM   #9
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Sorry about multiple posts but I can't figure out how to edit. The Fuel Pressure is ~30psi at idle then after it shut off it went down to 20 psi the first time the next two times after shut off it went to 40psi. Is my fuel pressure tester bad or is it pointing to something.

Matt
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Old 02-03-2011, 07:23 PM   #10
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If you smell gas in the vacuum line, the FPR may have a leak. But that wont cause the fuel pressure to be low with it unhooked. The problem is when you WOT, you may be leaning out the engine and your risking chipping a piston that way. Your fuel pressure should be about 48 with KOEO
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