Mechanics

HIGH IDLE ISSUE AND INTERMITTANT SHIFTING CAUSE IAC, TPS?

1999 Buick Century • 170,000 miles

Hello, I have a 99 Buick Century and recently I have experienced very high idle speeds and erratic shifting issues. I have cleaned the IAC valve, and did notice my throttle body was rather dirty on the inside. I had cleaned the throttle body with a cleaner, cleaned the IAC, and started the car. The idle was still high. I disconnected the IAC, the TPS, the air box sensor, the sensor on the air intake tube and the EGR sensor, I thought the car should have shuddered or something, so it ran high still. I connected all the sensors back, started the car and still high. My next thought is to disconnect the IAC alone, then the TPS alone. Is there anything I am missing? I have seen others with the same problem, but have not seen any sort of resolution. I thank you for your assistance.
Dennis
AD
Avatar
Dlvaughn1963
September 24, 2012.



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

Saturntech9
Dec 31, 2012.
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
Dlvaughn1963
Dec 31, 2012.
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?
AD

Tiny
Dlvaughn1963
Jan 14, 2013.
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.

Saturntech9
Jan 15, 2013.
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
Dlvaughn1963
Jan 15, 2013.
You can buy a engine tilter made for that goes where the strut mounts go or a ratcheting tie strap or come along.

Saturntech9
Jan 16, 2013.
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.

Tiny
Dlvaughn1963
Jan 17, 2013.
I always put in the stock plug type no problems that way.I don't think the platnuim to double platnuim is causing the issue but I would put the stock plugs in anyways. Let me know what happens.

Saturntech9
Jan 17, 2013.
I changed two plugs #2, #4. I think when I put the seafoam in the breather tube n the vac line I may have fouled the plugs the two plugs I've changed have improved the performance. So ill replace the others.

Tiny
Dlvaughn1963
Jan 17, 2013.
Sounds good I hope you put the stock plugs back in.

Saturntech9
Jan 19, 2013.
Page 11 of 12

AD