HIGH IDLE ISSUE AND INTERMITTANT SHIFTING CAUSE IAC, TPS?

1999 Buick Century

Tiny

dlvaughn1963

December, 31, 2012 AT 5:16 AM

Can a bad O2 sensor cause this problem or is it truly a leak?

Tiny

dlvaughn1963

December, 31, 2012 AT 4:57 PM

You are gonna love this.
Had run out of options and tired of buying parts so. I looked at routing of spark wires and all of them were good plug to right coil. However. I did find the #3 plug wire NOT clipped I the top of the plug. So I checked them all and started the car and I had a single hiccup and surge and immediately the idle went away. So for anyone who reads this thread to the end random misfire check all cables for connection. Random multiple misfires DO typically point to something in the ignition/timing discrepancy. It took three months to get to this point and I believe that if I would have changed the ICM I may still have not fixed this. Truly the craziest and most challenging of problems always have the simplest corrective action. I did have some minor initial drive rumbles with acceleration but the ECM quickly returned the engine to normal operating parameters. Thanks for your assistance and suggestions for fixing this idle/rpm misfire dilemma.
Dennis

Tiny

saturntech9

December, 31, 2012 AT 8:32 PM

Your welcome glad to hear you got it fixed. Its crazy sometimes what we find the cause of the problem is.

Tiny

dlvaughn1963

December, 31, 2012 AT 11:00 PM

Well it's intermittent just not as much as before.
Still checking possibility that the ignition wires may be bad, or the wires might be sitting on the exhaust manifold. But again I'll recheck. More to come

Tiny

saturntech9

January, 2, 2013 AT 2:03 AM

Keep me posted.

Tiny

dlvaughn1963

January, 14, 2013 AT 10:29 PM

Do I need to start a new thread for my continuing problem?
I'm at my end with this problem. I thought it was a spark plug issue, but it seems not. My question now is this. If the ICM is bad, will it cause misfire, or is it possible I just may have a bad plug? I did a cold run on the car just to time and see when the problem actually happens. It seems that at first crank, all is good. Then every 30 sec or so, the misfire starts, then the engine revs up then comes back down. When I loaded the engine (a/c and lights, trans in rev) the engine settles and the misfire is not as pronounced. Then returning the engine to a no load, it is fine. The misfire is so intermittent, that on occasion the CEL flashes when depressing the accellerator, and a lack of power from the engine is observed. After about 2 min the problem is almost gone, but when in park, or sitting at a traffic light, the misfire continues. IF there are codes will the problem persist, or will clearing the codes cause the computer to relearn the engine parameters?

Tiny

saturntech9

January, 15, 2013 AT 5:16 PM

We can stay with this thread a ICM will not case just one cylinder to missfire. So we know which cylinder is misfiring? Also what codes keep coming back is it just that P0174 and the P0300?Its strange it will missfire when its not under a load?Does it mostly miss fire at idle?Also clearing the codes will reset your emissions monitors so they will have to be relearned.

Tiny

dlvaughn1963

January, 15, 2013 AT 6:17 PM

I have not checked codes yet, it misfires at idle, and when I drive the car for about two minutes or less then the misfire occurs but not as pronounced. When I do press on the gas the engine boggs down. I wonder if I may have a bad plug? All the ignition parts are new, and I understand the ICM either works or doesn't. I have to purchase a strap so I can rotate the engine to check out the rear plugs. Will do this on my next few days off. I will have plenty of time to do something.

Tiny

saturntech9

January, 16, 2013 AT 1:45 AM

You can buy a engine tilter made for that goes where the strut mounts go or a ratcheting tie strap or come along.

Tiny

dlvaughn1963

January, 17, 2013 AT 4:16 PM

I was able to buy a strap pretty cheap and got the engine rotated. I changed the plugs but I'm not entirely sure why it's still rough when I pulled the plugs #2 & 4 had some white deposits on them but could not tell if they were truly deposits or just not burning hot. It's also possible that the orig spec plugs r double plat. Should it make a diff that platinum plugs were used and not double? I pulled regular plugs out of the engine when I first started this work three/four months ago. I'm now waiting to see if the codes will clear with the batt disconnected. More to come.

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