Some minor issues - fluctuating RPM, A/C turning off car, etc.
VitriolicChemistry
12-20-2009, 02:23 AM
Hey everyone,
I'm new to the forums and don't really know much about the technical side of cars, but I understand basic terminology and enough to not get ripped off.
Anyway, I have an '03 3.8L Monte Carlo. It's been immaculately maintained by my dad for the past 6 years and he's taught me some stuff, but I took it with me to college back in August and I've noticed some minor issues that have come up that I haven't had time/money to address yet, but will soon. I haven't had the "Check Engine" light come on or anything like that. Here's a quick rundown:
1. Floor mats wet after rain - I assume this means that there's a leak somewhere. It's probably worn weatherstripping, but could it be something else? If it is the weatherstripping, is it easy to replace yourself if you've never really done that kind of thing before?
2. RPM idle fluctuates between about 700 and 1500 RPM when car is in park, especially just after the engine turns on - So yeah, I'm not really sure what the deal is here. Back in August I had my brake booster replaced and the mechanic said this problem had stemmed from a vacuum leak/dirty air filter and that it should go away now that the booster and air filter had been replaced. However, it hasn't.
3. Turning off the A/C when car is in park sometimes causes the engine to shut off - I habitually turn off the A/C when I put the car in park. When I do this, it almost always causes the RPM to fluctuate (related to problem #2 perhaps?). Sometimes, it causes the car engine to shut off and the display lights come on as if I've just put the key in the ignition. This doesn't happen if I turn off the A/C while driving.
4. Very recently, I noticed the volt meter had begun fluctuating - I don't remember exactly when it happened - I may have been pressing on the brake while in park or something. Basically, when I hit the brake, the reading dropped to about 10-11 amps...when I released the brake it went back up to 14-15 amps (very rapidly). This doesn't happen while I'm driving.
5. Occasionally hear a "thud" noise when braking - Sometimes when I gradually brake and come to a stop (say, from about 30 MPH to rest), I will hear a dull "thud" noise, possibly toward the back of the car, right as it comes to a stop.
6. Occasional "squealing" during braking - The brakes still work very well, or so it seems. Maybe the brake pad is worn/damaged?
Any help is greatly appreciated. Thanks. :)
I'm new to the forums and don't really know much about the technical side of cars, but I understand basic terminology and enough to not get ripped off.
Anyway, I have an '03 3.8L Monte Carlo. It's been immaculately maintained by my dad for the past 6 years and he's taught me some stuff, but I took it with me to college back in August and I've noticed some minor issues that have come up that I haven't had time/money to address yet, but will soon. I haven't had the "Check Engine" light come on or anything like that. Here's a quick rundown:
1. Floor mats wet after rain - I assume this means that there's a leak somewhere. It's probably worn weatherstripping, but could it be something else? If it is the weatherstripping, is it easy to replace yourself if you've never really done that kind of thing before?
2. RPM idle fluctuates between about 700 and 1500 RPM when car is in park, especially just after the engine turns on - So yeah, I'm not really sure what the deal is here. Back in August I had my brake booster replaced and the mechanic said this problem had stemmed from a vacuum leak/dirty air filter and that it should go away now that the booster and air filter had been replaced. However, it hasn't.
3. Turning off the A/C when car is in park sometimes causes the engine to shut off - I habitually turn off the A/C when I put the car in park. When I do this, it almost always causes the RPM to fluctuate (related to problem #2 perhaps?). Sometimes, it causes the car engine to shut off and the display lights come on as if I've just put the key in the ignition. This doesn't happen if I turn off the A/C while driving.
4. Very recently, I noticed the volt meter had begun fluctuating - I don't remember exactly when it happened - I may have been pressing on the brake while in park or something. Basically, when I hit the brake, the reading dropped to about 10-11 amps...when I released the brake it went back up to 14-15 amps (very rapidly). This doesn't happen while I'm driving.
5. Occasionally hear a "thud" noise when braking - Sometimes when I gradually brake and come to a stop (say, from about 30 MPH to rest), I will hear a dull "thud" noise, possibly toward the back of the car, right as it comes to a stop.
6. Occasional "squealing" during braking - The brakes still work very well, or so it seems. Maybe the brake pad is worn/damaged?
Any help is greatly appreciated. Thanks. :)
CJ0717
01-26-2010, 02:00 PM
Here's my take on some of your issues. The fluctuating idle no doubt is due to excess air entering the upper intake plenum or lower intake manifold. This causes a lean condition and the computer compensates by adding fuel. As the fuel is added the RPM goes up and then fuel is cut back to lower the idle down to 700-800 RPM. Then the air leak again leans out the engine and this happens again and again. The revving will go up and down forever at an idle. Once you are driving it apparently disappears. This is only due to the fact that more air is needed due to more fuel being used and the computer is OK with that. Nonetheless you need to find the leak and fix it. Usually a gasket has failed and needs to be replaced. You can temporarily get by by finding the leak and spotting some RTV sealer at the point of the leak. Won't last forever but it should get you by for a while till you schedule a few hours to replace the gasket. My bet is the upper plenum gasket. A shot of some water from a spray bottle will find it.
Your issue #2 and 3 may go away when #2 is fixed
The small thud after a stop may be your rear brakes. The squeeling may also be the same. I assume you have disc brakes all the way around. Usually the rear calipers tend to freeze. Maily due to lack of use. Front Brakes do about 80% of the work while the rear do the rest. When a caliper freezes you may be hearing a brake pad slapping. Check for any corrosion on the rotors. If it's drum brakes in the rear the shoes may be shot and you will get a thud occasionally. Especially when turning a corner at 10mph and up.
Lastly is the water under the floor mat. Make sure its water and not coolant. (bad heater core). Sometimes the floor under the carpet rots out and any water sprayed up from the road leaches through and will soak your carpet. It will only get worse as time goes by.
Your issue #2 and 3 may go away when #2 is fixed
The small thud after a stop may be your rear brakes. The squeeling may also be the same. I assume you have disc brakes all the way around. Usually the rear calipers tend to freeze. Maily due to lack of use. Front Brakes do about 80% of the work while the rear do the rest. When a caliper freezes you may be hearing a brake pad slapping. Check for any corrosion on the rotors. If it's drum brakes in the rear the shoes may be shot and you will get a thud occasionally. Especially when turning a corner at 10mph and up.
Lastly is the water under the floor mat. Make sure its water and not coolant. (bad heater core). Sometimes the floor under the carpet rots out and any water sprayed up from the road leaches through and will soak your carpet. It will only get worse as time goes by.
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