Intermittent SES & engine idle speed fluctuations (99GT)

Bruce123 · #1 11-10-2003, 09:47 AM

The SES light comes on intermittently - sometimes at startup (hot or cold), and sometimes while driving. The light may turn itself off after driving for a while, or may stay on. There is no noticable change in performance when the light is on. My mechanic read the code as something with the MAS, but since the SES light would not come on while he had the car (naturally!), he didn't replace anything (told me to keep an eye on it.). That was about 2 weeks ago...

More recently, sometimes at startup (hot or cold), the engine will idle up and down between 500 and 1700 RPM, sometimes slowing down enough to stall. If it doesn't stall, the idle will eventually settle at its normal RPM. This fluctuation does not coincide with the apperarance of the SES message. So far, this fluctuation of RPM is only at startup.

Any ideas on what could be causing these issues, or how to diagnose?

The Burning Rom · #2 11-10-2003, 03:47 PM

MAS?...did he maybe say MAF? MAF being the Mass Air Flow Sensor.

Bruce123 · #3 11-10-2003, 04:13 PM

Yes, Mass Air Flow Sensor- (what he wrote on the invoice is "MAS (mass air flow sensor)")"

The Burning Rom · #4 11-11-2003, 11:28 AM

Did he take the TB off and look at the MAF sensor? The screen could be dirty...or it could just be defective. What year is your car?

Bruce123 · #5 11-11-2003, 11:44 AM

It's a 99 GT, has 95k miles

He charged me $35 to clean, R&R the MAF, said it wasn't particularly dirty.

With the intermittent SES indicator and the idle fluctuation that doesn't necessarily coincide w/ the presence of the SES, I'm concerned that the problem may not be w/ the MAF at all, thus my interest in how to diagnose.

Thanks for your continued thoughts on this.

Phill Acio · #6 11-19-2003, 09:55 AM

Question.... have you noticed an increase in your fuel consumption and does your exhaust smell real gassy when it decides to idle high. I think im having the same problems as you, but i have a different engine than you. I'm curious.

dplata · #7 12-02-2003, 03:39 PM

Did replacing the MAF work? I'm curious because my wife's car is having that problem. The SES light comes on and the engine will also idle up and down. I was told it was the MAF but I'm curious to see if it worked for you.

GTPgirl · #8 12-02-2003, 09:41 PM

Shortly after I got my GTP, I had that same problem. Intermittent SES light, high idle. The code it was throwing was MAF. There was a crack in the top of my MAF (how it got there I have yet to figure out). My dad thought he could do some engineering on it and make it work (He's ASE master tech) and he couldn't. We replaced the MAF, and everything has been fine since.

ydtrack · #9 12-02-2003, 10:47 PM

Sounds like a bad MAF sensor. I picked one up off a junk car until I could get a new one. The whole throttle body from the junkyard only cost $40.

GTPgirl · #10 12-03-2003, 01:16 AM

Well, when I got my GTP, I had just wrecked a '97 Bonne SSE, and they have the same MAF sensor. So we just swapped the one off my GTP for the one on the Bonne. So mine was pretty much free, lol

GTPCatz · #11 12-06-2003, 10:07 PM

could also be a cloged cat.....
I know when my Cat was cloged on my 99 it had a very rough idle....no SES light though

kilroypr · #12 12-09-2003, 05:41 AM

Well the MAF sensor is not really expensive and modern cars either come with a Air Flow Meter or a MAP Sensor to determing the airflow into the throthle body and regulate fuel mixture. IF it does not work correctly you car could have a rought idle, hesitation or herratic idling.

kilroypr · #13 12-09-2003, 06:04 AM

you should replace it

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