HIGH IDLE ISSUE AND INTERMITTANT SHIFTING CAUSE IAC, TPS?

1999 Buick Century

Tiny

saturntech9

December, 18, 2012 AT 7:26 AM

Try lightly tapping on the mass air flow sensor with a screw driver handle see if it runs any different?You could also try cleaning the mass air flow sensor with some mass air flow sensor cleaner.

Tiny

dlvaughn1963

December, 18, 2012 AT 4:57 PM

I unplugged and plugged the sensor, ran engine no change. Cleaned the MAF sensor last month, got no appreciable difference in performance. I'm not ruling out some sort of either gasket leak or possibly maybe even really bad fuel injector clogging. However I have read it will cost me quite a bit for gasket work, and I'm not gonna spend this much money on it. Ive only known about this misfire condition until I fixed the high idle issue. I'm at a loss now. The only part I have not changed is the ICM and Ive read that this component is either good or bad.

Tiny

saturntech9

December, 18, 2012 AT 5:17 PM

So do you have any codes right now in the computer?Also did you check for vacuum leaks?If so how did you check for them?

Tiny

dlvaughn1963

December, 18, 2012 AT 5:47 PM

Still have the random misfire.I don't have a smoke generator, I don't smoke a cigar or cigarette ( the cheap smoke generator so I read : ) ) I have sprayed the top of every seam and gasket of the car with a mild soapy solution to chase a leak, and have not found one. I have read that 99 Buick centuries are famous for clogging fuel injectors, I've run two cans of seafoam in my tank and there has been a slight increase in performance. The ransom misfire and idle stumbling does not happen when the engine is first started. It runs fine for about 20 sec. Then as the engine runs, I guess the electrical signals from whatever goes through the engine computer. The engine then starts the cycle of high revs with the first one higher revving then tapers about every 10 seconds for roughly 5 cycles. Then the engine settles with the misfire. When the engine throttle is moved instead of a smooth acceleration, it stumbles and at a certain point will quickly accelerate. So I think one of two things is going on. Either I have a vac leak still, or I have a horribly clogged fuel injector. The misfire does seem to go away, but not entirely.

Tiny

saturntech9

December, 19, 2012 AT 1:07 AM

I really dont see how soapy water can find a vacuum leak since a vacuum is the absence of air pressure so no bubbles are going to form. You use carb cleaner and look for rpms going up or down stumbling etc.

Tiny

dlvaughn1963

December, 19, 2012 AT 2:24 AM

Will try again but got no rise in rpms

Tiny

saturntech9

December, 19, 2012 AT 2:31 AM

Iam thinking vacuum leaks with the unstable idle have you tried cleaning the idle air control valve?

Tiny

dlvaughn1963

December, 19, 2012 AT 5:14 AM

Replaced the idle air control valve

Tiny

dlvaughn1963

December, 26, 2012 AT 4:55 PM

Merry Christmas.
I'm really at a loss. It seems like what ever I think maybe the issue is not. I am thinking now it is some sort of seal leak. When the engine is cold initially it runs nicely for about a minute, then the random misfires occur, and stay until the engine reaches optimum temperature. Once the engine is allowed to cool, then the misfires come back, then goes away when the engine has reached the optimum temp. When the misfires occur, the engine is very sluggish to the point of stalling. Then once warm, the acceleration is normal, and so is the idle. I'm thinking intake manifold from the throttle body? My intake manifold is NOT plastic, but looks like cast alluminum. Is this gasket normally an issue or is it somewhere else?

Tiny

saturntech9

December, 27, 2012 AT 1:00 AM

I have seen clogged fuel injectors cause random miss fires a smoke test is the best way to find vacuum leaks.

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