RPM's fluctuating at start up

Hi,

I just recently bought a used 2002 Mazda Protege. I've noticed that during start up the RPM's seem to fluctuate between 1000 - 2000 RPM's. It seems to make this big jump once or twice, then does small fluctuations between 1000 and maybe 1200 RPMs before settling down around a normal (I think) 800 or so. Do you know what might have caused that? The car was just inspected last month. She said she had a technician look over the car before selling it, though I have a feeling the private seller may of blatantly lied to me about a couple things when asking about the car, but alas. Here we are

Any ideas what might cause that to happen on one of these cars and how much it might cost to fix? I did some searching around but didn't really know what to expect for a Protege specifically.

Thanks!

A jumping idle often indicates a dirty/bad EGR valve, at least it did with my 89 MX6 GT.

By the way, didn't you drive the car before you bought it? Also, as a general rule of thumb, don't buy from a female unless she or her husband is a mechanic. Single moms with low income tend to be the worst maintainers.

We did take it for a drive, but she already had it warmed up since she was driving it beforehand so I hadn't noticed. Also realized it eats through coolant like there's no tomorrow. She had it all topped up when I was looking at it and when I specifically asked if she ever need to re-fill coolant or had any issue with fluids she flat out said no and of course went on about never having any troubles with it. Taking it to a mechanic next week and will see what happens. Certainly learned my lesson though.....even though it was the hard way since I'm out valuable money...

check egr valve. might be dirty or going back. check for vaccum leaks.

any check engine light?

When warming up, the ECU trys to maintain a slightly higher RPM to heat the engine up faster. It does that for 2 reasons: to get the O2 sensors up to heat so they can read correctly, and to heat up the catalytic converters for improved emissions.
Since the throttle plate is controlled with a cable, the ECU can usually only modulate the idle with an idle bypass valve located in the throttle body so it can pull extra air in. I'm not positive how it is on the protege, but it should be something like that. If you already knew all that, then forget I said anything about it. Why do i mention it? because I'm getting to all the sources of your problem.
There is also an evaporative gases purge control valve connected to the intake manifold that the ECU can open to get more fuel and air from the gas tank. The EGR valve is used to pull possible unburned gases in from the exhaust manifold (to further improve emissions) but it can get stuck open by carbon build-up. Both are solenoids.

there are other possibilities like vacuum leaks in other random hoses or the brake booster, but those would cause constant problems and not just at warm-up. If it's fluctuating, then the ECU is trying to modulate air to maintain the high idle, so my guess is that it would have to be from one of those things that it can control: the idle bypass valve, the EGR valve, the purge control valve.

the Mass Air Flow sensor has to be hot in order to work, and it doesn't serve a purpose to the ECU until the O2 sensor is hot too, so you can rule that out. Oh, and the Intake Air Temp sensor as well. The ECU doesn't use it until the MAF sensor is good to go.

So there you go. Those are your best candidates. Choose for yourself which ones you wanna check out. If you don't want to just buy replacement stuff till you find the problem, you might want to read the Factory Service Manual for tips on how you can check the solenoids and stuff for faultiness. Generally it'll direct you to look for the internal resistance of components.

oh yeah. where's your coolant going? if it's not just leaking on the ground, then don't ignore that. In fact, check your oil filler cap and/or dipstick periodically to make sure it's not in your oil. coolant makes oil a little milky. Elsewise it's probably getting burned=>cracked head gasket. burning coolant produces white (i think?) smoke, so that could be a clue. If you do have a cracked head gasket, then your compression could be low in a cylinder or two, and the ECU is just struggling against it to try to make the warm-up idle. Compression might get better when the cylinder heats up and the rings seat, so it might not be so noticeable when warm.

just some thoughts.

jdoggsc said:

oh yeah. where's your coolant going? if it's not just leaking on the ground, then don't ignore that. In fact, check your oil filler cap and/or dipstick periodically to make sure it's not in your oil. coolant makes oil a little milky. Elsewise it's probably getting burned=>cracked head gasket. burning coolant produces white (i think?) smoke, so that could be a clue. If you do have a cracked head gasket, then your compression could be low in a cylinder or two, and the ECU is just struggling against it to try to make the warm-up idle. Compression might get better when the cylinder heats up and the rings seat, so it might not be so noticeable when warm.

just some thoughts.

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Thank you for all the details! There is an engine light on, however she told me that her technician got a read code that it was an Air Sensor of some type (though maybe she was lying, again).

There's no noticeable leak with the coolant. I checked under the hood and nothing is wet either. The coolant seems to get "eaten" pretty fast, actually it seems a bit alarmingly fast. It was driven a bit during the test drive, then back to my place (maybe under 5 minute drive) and then started a couple times through the week and I drove it back/forth through my (very) small driveway a couple times (I wanted to see if the coolant would drop any, car isn't legal yet). It dropped a noticeable amount in the coolant tank during just this amount of driving(checked it 24 hours later). I don't see any white smoke coming from the car. I thought maybe it might just be a slow leak somewhere, but I've had that before in a car and the coolant certainly didn't drop as fast as it does here. Would it be extremely noticeable if the head was warped on the gasket? I'm trying to rule out worst case scenario. I could barely afford the car, let alone replacing a head on the gasket.....

Thanks again, I'm going a bit crazy not knowing what it might be. Just have to hope for the best, otherwise I'm out a car and $850 dollars.

Gaia said:

let alone replacing a head on the gasket.....

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well we might be worse off than i initially thought. The top end of the engine is called the head. it's the part with the valves and the cams and the spark plugs. It's a separate chunk of metal from the rest of the engine (sometimes called the "short block"). There's a specially shaped part (kinda like a piece of paper, but it's not paper at all) that goes between the two when the engine is assembled to make a good seal between the two.

No, you cannot tell by looking at the engine that the head gasket is broken somewhere. you have to pull the engine head off of the engine block to check it. (unless someone here knows of a better way). It's not a trivial process, and is considerable engine surgery. If you're not feeling mechanically inclined enough, don't have any friends who are, and don't have the money for a mechanic, then i don't know what to tell you.

again, that's if it's the head gasket. Wait a little bit for someone else's input. I've only had my mazda for 2 months, so I don't know the car as well as someone else might.

Does the car run hot? There is a way to tell if combustion gasses are being injected into the coolant. Radiator shops and some auto repair shops should be able to test the antifreeze.
If the oil is not milky, there has to be white smoke. Have you had someone follow you to verify?

I know this is water under the bridge but never drive a for sale car when it is already warmed up. One of the oldest tricks in the book for an unscrupulous seller to disguise problems is to have the car all warmed up, just before the potential buyer arrives. Another "slider" here in CA is for the seller to tell the buyer that either he or she must smog the car or that the seller will have the car smogged only after the buyer pays for it. I ALWAYS ask to look at the smog test results before go any further with my inspection. If the seller refuses to show me one, I walk away.

Anyway, I hope it's not something expensive. Some city/community colleges will work on your car for free. You might check into that (if any are in session).

hi you could also check your heater core to see if it is leaking at all and also have someone stand behind the car while you hold gas petal till your rpm hits 3 and hols it for a few minutes to see if the smoke or any water comes out the tailpipe.i just replaced the headgasket on my 2002 mazda protege lx cause it was running like crud and leaking through the exhaust but i didnt have any smoke..the high rmp would have to be one of the items listed above best case would be maybe check all of the Vacuum hoses or the main air flow tube may have a crack in it they are famous for that and advance auto can order you one cheaper than a dealership it will run $36.99 plus tax and take like 3 days to get check it first .....................hope this helps ps here is the part number(( Part No. 696-601)) for that hose as they may try n tell you they cant get it but they can i just did last week