6th Dec 2009, 16:58

1998 Mazda 626 LX - Had same intermittent idling problems when stopped (at light, sign, etc.) but it went away on its own (it seemed). I thought maybe the wife had been putting crappy fuel in it, or that it had something to do with disconnecting the battery (i.e. resetting idle parameters in ECU?).

Had to replace transmission recently. Left the repair shop with car running fine, then Over-Drive light began flashing after driving 100+ miles. Coming to a stop led to same idling problem (except more severe). Apparently some wire broke and ECU couldn't regulate engine performance properly.

Will update later if the car doesn't continue to run properly.

7th Dec 2009, 09:38

My protege has this kind of idling issue as well. I suspect a bad fuel pressure regulator. It is also accelerating unevenly during warm up.

Check the vacuum line that goes from the manifold to the fuel pressure regulator. See if there is gasoline in it, or if it smells like gasoline. If it does the regulator's membrane is leaking. That enriches the fuel mixture through that vacuum line and can lead to all kinds of symptoms.

17th Jan 2010, 22:23

1998 626LX 2.0

Same idle problem as all the rest. After reading all the reviews, doesn't anyone have a solution to the problem? It's not very useful to post here unless someone has an answer.

Like everyone else, I guess I'll just wait.

20th Jan 2010, 13:01

Can someone PLEASE help me! I'm at a loss as far as finding the problem.

First off, I fix cars but only know the basics. Tune ups, brakes and that's about it.

I had a bad TPS - Throttle positioning sensor. The car always died when I let off of the gas. A friend checked the sensor with an ohm meter and it was bad, so I bought a new one and he installed it. He also checked the new one with an ohm meter, to make sure it was within specs and it was fine.

Now, the car doesn't die, but the idle won't stay consistent. Once it drops to 1000 rpms, it jumps up to 2000 rpms. It continues to do that. It just jumps up and down.

I took off the battery cable after installing the sensor, to reset the computer. I let it run for over 5 minutes and it continues to do the same thing. The car has new plugs, wires, PCV valve, mass air flow sensor, air filter, oxygen sensor and all hoses are fine. A guy told me that I have to have the computer error codes cleared out, to allow the car to run properly. Is that true?

My main question is what the heck could be wrong? When he put the TPS in, he put it in with it "turned" all the way, in one direction. The holes for the screws are oval and it seems to me it can be "adjusted". Does it matter how that sensor is installed? If I move it to the center of the holes and tighten it back down, would that possibly help?

Also, we can't seem to find any vacuum leak. When the mass air flow sensor is disconnected, the car runs at an even idle but it still runs high at 1500 rpms. I can't even drive it with the mass AIR flow disconnected, because the tranny "slams" into gear. The minute I hook it back up, it jumps from 1000-2000 rpms and keeps jumping up and down and won't idle at a specified rpm. Do you have any idea what could be wrong?


18th Feb 2010, 10:58

Same car, same idle problem.

My next door neighbor hooked up a smoke machine to the pcv vacuum line, and noticed there was a leak in the intake manifold gasket. He replaced the gasket and no more idle problem.

I haven't reset the ECU yet, mainly because it's running good now, and the old adage, "if it ain't broke, don't fix it".

I'm concerned now that the ECU still has a "memory" of when it was idling poorly, and if resetting the ECU will "relearn" starting from scratch? I guess I'll just give it a try and see what happens.

Oh, I did the above after replacing both the IAC valve and MAF sensor, to no avail.

23rd Feb 2010, 07:22

FYI, if you unplug your mass air flow sensor, the car will go out of closed loop operation, this will allow your car to idle at stops, and actually allow it to run. But the check engine light will come on. But that should let you drive it while you are trying to get it repaired.

BTW my car needed the intake gasket. Tested it by letting it idle, then sprayed the intake gasket with carb cleaner. If the vehicle dies or idles higher, then the gasket is leaking.

28th Mar 2010, 01:16

I need help with this problem I am having with my 1998 Mazda 626 V6 stick... OK.. I just put another motor in the car because the old motor went... so I start the car up and it started.. I left the car on for about 45 seconds.. then I turn it off.. Now the car has been sitting for about 10 months.. the reason why I turned the car off is because I had to do a oil change, because the motor I just put in had old oil in there, and I didn't want that oil in the car.. So I changed the old oil and put new oil in it.. Then I tried starting the car; it wouldn't start.. it cranks, the belts turn, but nothing happens.. I checked the spark plug wires and I wasn't getting ANY spark or no fuel.. Can anyone help me that might know the cause of this problem.. THANK U... email me.. sportcarlover43@yahoo.com

5th Jul 2010, 20:07

Okay I have a 1998 Mazda 626 that was running perfectly fine until I took it for an oil change. After the oil change was completed the car would not start up. I waited two days and still the car will not start. Do anyone have any suggestions as to what the problem is?

If so you can contact me at mrz_ashley@yahoo.com.

15th Nov 2010, 19:10

I have a 1998 Mazda 626, 2.0, 78500 miles with the same idle issues in drive, shakes all over. I have replaced the intake gaskets, throttle body, fuel filter, plugs and wires, reset the ECU, cleaned the IACV and replaced the TPS. Now I am in the corner, I don't know what's my next step. I went on line for auto recalls; they have 5 so far, relating to fuel issues, but nothing for rough idle (I need help).

13th Dec 2010, 08:08

To the guy who posted in March. No spark no fuel can usually only mean one thing. Crank sensor. At least in my experience that has been the problem and they sometimes go bad when doing an engine swap.

6th Jun 2011, 21:31

Crank sensor..

11th Mar 2013, 15:45

First of all, to set the TPS, adjust it so you hear a click just as the accelerator cable i.e. the gas pedal is pressed. The cam or lever the gas pedal cable connects to; as soon as the pedal causes the accelerator to move, you should hear the click. If this doesn't fix the issue, check the O2 sensor.

11th Mar 2015, 01:44

I just fixed my 1998 Mazda 626. It won't idle. The idle was going up and down. I put a mass flow air sensor and an idle air control valve on, and that didn't do it, and I put an intake manifold gasket on, and it worked - try that.

17th Sep 2015, 02:42

Run automatic transmission fluid in the gas for three full tanks and that should clear up most of your problem, and it's cheap and it will not hurt your car. I run automatic transmission fluid in my oil, I run it in my gas, and my car runs smoothly. My 1998 626, the idle would start searching, going down the road or at stop signs, and mine cleared up.

11th Dec 2016, 02:43

A fluctuating RPM is the number one symptom of a bad intake manifold gasket. As the ECM tries to cycle off and on adding fuel to compensate for all the unmetered air, a loop effect happens... lean mixture... More fuel... Upstream O2 sensor sees it as rich... (Downstream O2 sensor sees it as rich, or not, and if not your precat is getting killed anyways)... And the fuel is then lessened to once again create the lean mixture, setting the next cycle of fluctuating RPM.

14th Jul 2017, 13:56

I got an idle air control valve at a junkyard for 5 bucks; works fine.