1998 Chevy Cavalier High Idle RPM
 

Hello everyone,

I am having an issue with my 98 that I was hoping to get some assistance with.

So basically, the idle RPM is abnormally high. I have an idle speed of 50 mph. At first, my motor would drag my car even when the brakes were fully applied (foot on the ground).

Now, my car actively tries to stall. Working on it, I found out that if I cover my hand on the air intake, the car idles normally.

My conclusion is that it is getting too much oxygen and thus burning too rich. I noticed that as my car idles, the manifold can get hot, red hot.

With this, my first logically conclusion is the MAPS sensor is bad. The PCM uses readings from the MAPS and the IAT to determine the fuel/air mixing ratio. Using the OBD, it was discovered that the computer is seeing an 60 kPa reading from the MAPS at idle. I then unplug the MAPS and using the OBD reader, it reads 10 kPa (simply because the sensing pin is floating at this point.). The car then proceeds to idle normally. I am thinking that the MAPS is the one causing the issue.

Now, to save some money, I got a "new" MAPS sensor from the junkyard (This was free). After swapping mine out and connecting the "new" sensor in, there was no change in the performance of the car.

So, I am hear to ask the community if anyone has had this issue before and they did to correct it. Please, any information will be much appreciated.

I have a few ideas what else could be wrong (only 2 actually). The "new" sensor is actually faulty like mine and I need to just get a new one from the store. Or the Idle air control valve needs to be replaced. I am not sure if there are any code of the Idle air control valve but from my first conclusion that too much oxygen is getting into the system, a fault on the valve would make sense.

Please, what do you guys think? Or should I be looking elsewhere?

On a side note, with the MAPS sensor plugged in (mine and the junkyard), the car's acceleration was still quite good. (Somehow, a friend of mine was able to push the car to 100 mph for a time but stopped because I was fearful for the car!)

Not sure MAPS sensors really ever go bad.


"I have an idle speed of 50 mph" <--- WHAT?? not sure what that means. Please talk IDLE RPM...

"a friend of mine was able to push the car to 100 mph for a time " <--- Are you still talking in Park or where you on the highway at 100 mph?!

Look for dry rot and cracks on all your vacuum hoses and connections. Especially something you might have touched recently - like lines around the battery that you may have just replaced. Southern cars in dry areas that sit in the sun all day are more susceptible to such things.


Anyways - did you check to see if your catalytic converter is glowing red too? If so - it's probably plugged and melted... which may be caused by an ignition problem (coil or otherwise).

Lol sorry,

let me clarify a little bit. When I mean idle, I do not put my foot on the gas pedal and the car accelerates until the speed is 50 mph.

Yes, we were on the highway going 100 mph.

No, I haven't had the thought to check that.

Awhile back, water came through the air intake. Luckily, the engine was not running for very long so it never got hot enough to hydolock the car. So I was thinking that something in the air intake was damaged. But, I guess I could see the converter being an issue. That would cause blockage and a build up of pressure thus leading to a higher pressure reading.

Oh, I had thought that I posted this.

So if the catalytic converter was clogged, would the car still have good acceleration and would there still be a decent amount of exhaust coming from the tailpipe?