1996 Mazda 626 car idles extremely strange

DELBERT

MEMBER
1996 MAZDA 626
4 CYL
2WD
MANUAL
150,000 MILES

My 1996 Mazda 626 is doing a few strange things.

When the weather turns cold the car revs up and down between 1500 and 2500 rpms very rapidly while I sit idle. This will go away after it warms up and I drive it past 3rd gear, but will often return when I am in stop and go traffic. After I get off the highway and sit at a stop sign or stoplight it will worsen when I start moving again. It also is very jerky when I'm in 1st, 2nd or 3rd. I've read that this may be an oxygen sensor problem?

Also, the car seems to start overheating when I have the heat on. I don't think it's actually overheating because the minute I turn the heater off the temperature drops back to normal within 10 seconds.

I currently have a small crack in the radiator and have to add fluid more often then normal (maybe once to twice between oil changes). I added some radiator leak sealent today and some fresh antifreeze. The car idles much better and is not jerking in low gears, but I still am having a problem with the thermostat rising while the heat is on. I have no idea what's wrong, but it seems like it may be a combination of a few things. Help! I live in Minnesota and it's cold! I need the heater! I don't seem to have this problem in the summer.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi:
Interesting problem. The heater core should be acting like a small radiator helping to cool the engine. What is strange is the running problem and the heating problem. If I had to guess, it has something to do with the temp sensor. That could have an effect on both items, running and heating. Have you had the computer scanned for codes? Most nationally recognized parts stores will do it for free. Maybe you should try that to see if any codes are stored. Also, what type of rad sealer did you use? Some of them can cause a clog. Finally, and then I'll let you go, does the overheat problem seem to happen with the defroster only or either the def or heat?

Joe

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Tuesday, November 18th, 2008 AT 10:23 PM

DELBERT

MEMBER
2 POSTS

Thank you for you fast reply!

No, I haven't had the computer scanned yet. I could just take it over to Checker/O'Reilly to have this done, right?

I just used the standard Bar's Leak Sealer. Do you see this as a problem?

I can only confirm that it happens with the defroster. I haven't been using the normal heat.

So you don't see this as having anything to do with the oxygen sensor?

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Wednesday, November 19th, 2008 AT 10:33 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi:
Bar's leak is fine. I was hopping you would say that. As far as the codes, I don't recognize the name you mentioned. As long as they will do it, it's fine. At this point, I feel the O2 sensor is safe.

Let me know what code they find.

Joe

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Wednesday, November 19th, 2008 AT 3:36 PM

LIVEBIGFOREVER

MEMBER
1 POST

Hi, I would have private messaged this, but it denied me in fear that this would be spam. (You need 10 posts to PM, and this is my first)

I have the exact same car, make model year, with the exact same problem.

Only difference is I live in Syracuse not Minnesota!

I am wondering if you had been able to find out the answer to your problem since posting?

As we speak I'm letting her cool down so I can check the anit-freeze, which I have a feeling is part of the problem. I used to have a leak.

Also if you're not already, I reccomend using dry-gas when filling up. It seems our cars live in a paralell universe so I assume you may have had some trouble starting up in the past on really cold days.

Thanks

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Wednesday, February 4th, 2009 AT 8:31 AM

ACZELKRI

MEMBER
1 POST

Hi!

Have you managed to solve your problem with idling?

I had the very same problem, my idle rpm changed very rapidly between 1000-200rpm when the engine was halfway between cool and warmed up. I had a radiator leak, and my engine coolant was almost totally gone. After I refilled my radiator the problem more or less went away. However, one thing still remains:

After the engine has warmed up, idle rotation is 1200-1400 rpm. The idle will go down to normal (800) if I slow down the engine by putting it into 5th, while coasting to a stop. When the clutch engages, it forces the engine to turn slower, and usually it stays there.
The other trick I found was turning on some electric devices of high power consumption (like forcing the power window motor to pull up the window when the window is already up). This also has the effect of slowing down the engine, and once its rpm is decreased, it stays there.

Please, if you found a solution, post it here!

Best regards
Kristof