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Stanthe626man

Rough Idle Issue

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Hello all,

I recently came across this thread due to my 1998 626 having a rough idle after getting it back from the shop. Around November 2018 (Thanksgiving) my fuel pump went. I went to a junk yard with a buddy of mine and got a fuel pump from a junked car and put in into my car. We didn't drop the tank instead we cut a hole in the floor board under the backseat and replaced the part. When trying to start the car after replacing the fuel pump the car still would not start. The engine would spin as if it were going to start, but nothing... My friend who is a mechanic checked to see if the car was getting spark and fuel which it was, but the car still would not start. Just in case I bought a set of new spark plugs and installed them, but the car still would not start. We tried using starter fluid, but the car still would not turn over. Finally I had enough for that day and as it was the holidays I decided to just leave it and come back to the car later.

While the car was sitting my friend contacted me and said to check the crank shaft positioning sensor and see if it were dirty. I checked it and although it had some dirt/ old oil on it it was fairly clean, but I decided to go ahead and replace it anyway. Still no start.

Fast forward to last week. I had the car towed to a repair shop where they found that the timing was off and they corrected this issue and now the car starts and runs, but with a very rough idle especially on cold starts. There is not a check engine light on the dashboard. The guys at the repair shop suggested I take the car to a transmission repair shop due to the car jerking really hard when I put the car into drive. The guy at the repair shop adjusted the idle lower to prevent some of the jerking. When I am driving the car acceleration is hit or miss. Sometimes it accelerates normally and other times when I push the gas I get nothing, but a high rpm and a slowly accelerating car. At red lights the car shakes, jerks, and sometimes stalls due to the idle issue. Luckily I live in New Orleans which is flat so I don't have to worry about going up hills and can avoid most bridges.

If anyone has suggestions on what I can do to resolve this issue that would be great. Of course ideally I would like to find a Mazda expert here in the city, but thought I would check here first.

Thanks in advance for your help.

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46 minutes ago, BIGgame said:

Hello all,

I recently came across this thread due to my 1998 626 having a rough idle after getting it back from the shop. Around November 2018 (Thanksgiving) my fuel pump went. I went to a junk yard with a buddy of mine and got a fuel pump from a junked car and put in into my car. We didn't drop the tank instead we cut a hole in the floor board under the backseat and replaced the part. When trying to start the car after replacing the fuel pump the car still would not start. The engine would spin as if it were going to start, but nothing... My friend who is a mechanic checked to see if the car was getting spark and fuel which it was, but the car still would not start. Just in case I bought a set of new spark plugs and installed them, but the car still would not start. We tried using starter fluid, but the car still would not turn over. Finally I had enough for that day and as it was the holidays I decided to just leave it and come back to the car later.

While the car was sitting my friend contacted me and said to check the crank shaft positioning sensor and see if it were dirty. I checked it and although it had some dirt/ old oil on it it was fairly clean, but I decided to go ahead and replace it anyway. Still no start.

Fast forward to last week. I had the car towed to a repair shop where they found that the timing was off and they corrected this issue and now the car starts and runs, but with a very rough idle especially on cold starts. There is not a check engine light on the dashboard. The guys at the repair shop suggested I take the car to a transmission repair shop due to the car jerking really hard when I put the car into drive. The guy at the repair shop adjusted the idle lower to prevent some of the jerking. When I am driving the car acceleration is hit or miss. Sometimes it accelerates normally and other times when I push the gas I get nothing, but a high rpm and a slowly accelerating car. At red lights the car shakes, jerks, and sometimes stalls due to the idle issue. Luckily I live in New Orleans which is flat so I don't have to worry about going up hills and can avoid most bridges.

If anyone has suggestions on what I can do to resolve this issue that would be great. Of course ideally I would like to find a Mazda expert here in the city, but thought I would check here first.

Thanks in advance for your help.

I'm guessing it's a vacuum leak of some sort. Mine ended up being an exhaust leak, and I had to have my muffler fixed. It literally sounded like my car was cammed, but I literally had to throw a thermostat, coolant temperature sensor, new plugs and wires, an oil change, AND a thermostat with a replacement housing and new hoses, because the old thermostat housing snapped both bolts off at the heads. It ran like new with the exhaust leak fixed, but I only got one drive back from the muffler shop because the OEM thermostat got stuck closed and almost overheated the day after. That was about seven weeks ago...

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Thanks for that info @OldSix_95 reading your explanation makes me think my issue could be very similar. I may take it into a muffler shop and see if they will have a look. I have thought about the thermostat when seeing others post about the temperature sensor. Like I said on cold starts it's really bad, but once it warms up it gets a bit better. Not back to normal, but a lot smoother and it will start right up without me having to push down on the gas to get it to start. One thing I am wondering though... With my old fuel pump when I turned the key just before starting I would hear the fuel pump turn on, but now it only comes on when I'm turning the key to start the car. This makes me feel the pump is not priming thus I need to push the gas pedal when starting on cold starts. I'm tired already of spending money trying to figure out what's going on. I really wish there was a go to Mazda repair shop locally where I could take the car and they knew what to do instead of guessing.  

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17 minutes ago, BIGgame said:

Thanks for that info @OldSix_95 reading your explanation makes me think my issue could be very similar. I may take it into a muffler shop and see if they will have a look. I have thought about the thermostat when seeing others post about the temperature sensor. Like I said on cold starts it's really bad, but once it warms up it gets a bit better. Not back to normal, but a lot smoother and it will start right up without me having to push down on the gas to get it to start. One thing I am wondering though... With my old fuel pump when I turned the key just before starting I would hear the fuel pump turn on, but now it only comes on when I'm turning the key to start the car. This makes me feel the pump is not priming thus I need to push the gas pedal when starting on cold starts. I'm tired already of spending money trying to figure out what's going on. I really wish there was a go to Mazda repair shop locally where I could take the car and they knew what to do instead of guessing.  

I understand your frustration... my frustration with the issue was kinda doubled because of the fact that my ES-V6 is a '95, so OBD-I is a real pain to diagnose correctly. I knew for sure the tune-up was needed, but knew something wasn't right with the exhaust just by the sound alone. The next time you start it up, check to see if you smell anything abnormal, such as exhaust fumes around the car instead of in back. If you smell exhaust fumes while at idle, then you most likely have an exhaust leak

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13 hours ago, OldSix_95 said:

I understand your frustration... my frustration with the issue was kinda doubled because of the fact that my ES-V6 is a '95, so OBD-I is a real pain to diagnose correctly. I knew for sure the tune-up was needed, but knew something wasn't right with the exhaust just by the sound alone. The next time you start it up, check to see if you smell anything abnormal, such as exhaust fumes around the car instead of in back. If you smell exhaust fumes while at idle, then you most likely have an exhaust leak

Ok now I'm starting to worry... Tonight when I started my car to come to work (I work graveyard shift) the car started fine as it was a bit warmer today, but after arriving to work I left the car running for about 30 - 40 minutes while I was chatting with co-workers and after getting back in the car I smelled burning. Like something electrical... I parked the car and as I had to start working I just left it. Hopefully I won't be sending in a photo of a char-boiled 626 with my next post. Why does it always have to be fix one thing then another breaks type scenario with older cars??? smh...

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8 hours ago, BIGgame said:

Ok now I'm starting to worry... Tonight when I started my car to come to work (I work graveyard shift) the car started fine as it was a bit warmer today, but after arriving to work I left the car running for about 30 - 40 minutes while I was chatting with co-workers and after getting back in the car I smelled burning. Like something electrical... I parked the car and as I had to start working I just left it. Hopefully I won't be sending in a photo of a char-boiled 626 with my next post. Why does it always have to be fix one thing then another breaks type scenario with older cars??? smh...

I see... that one may have me stumped as well. But definitely have your car checked for exhaust damage...  had it not been for me following my gut instinct, I probably still would be trying to figure out why my car sounded and drove rough. My only issue now: finding a ride to go exchange the brand new battery that died.

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3 hours ago, OldSix_95 said:

I see... that one may have me stumped as well. But definitely have your car checked for exhaust damage...  had it not been for me following my gut instinct, I probably still would be trying to figure out why my car sounded and drove rough. My only issue now: finding a ride to go exchange the brand new battery that died.

Well, no photos of a burnt 626 to post. Grateful for that. When I got in the car this morning it still had a bit of the electrical smell, but started with me pushing the gas pedal in and I was able to make it home. Luckily I only live 5 minutes from my job. I'm off today and tomorrow so I will take your advice and take it to a muffler shop and see what they can come up with. Will let you know once I find out something.

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On 2/3/2015 at 7:47 AM, 626stich said:

i guess i just need to take it to a shop for a computer to verify what is wrong. The same issue is with my 2001 ford escort. i hear they are the same in a lot of ways. im not going spend the time to take my coil to some place to test my coil. It would be cheaper and more time appropriate to just change it out by guessing. if i had all the tools to verify all my problems then i wouldn't need a website to ask and have a response of "im not going to respond or help you" ... wow you must be single and a lot of time on your hands. Thanks anyway.

You can test the ignition module by using a test light, an old fashioned one with a real bulb, not the LEDs they have on many today. Remove the  cable from spark plug, Gnd the test light ground clip and BEFORE you start car put the test light probe tip on the cable spark plug terminal to give the spark a place to go. (see warning below). Start Engine and your test light now acts s the spark plug. Move the tip away slowly to see how far the spark jumps, until you reach a position where its barely able to jump.Put the probe back to tip then turn engine off. Do that on another module/wire combination and see if theres a big difference.

That difference points to a bad or semi bad cable or bad/weak ignition module output. No fancy tools needed. I did this and found a bad output on my ignition module and closer inspection I saw a crack on it, where energy probably jumped from it to GND at the module. The Mode 6 data said I had misfires on that cylinder, after I changed the module it ran great.

Make sure your hand is not close than the test light probe or you will get bit big time by the spark.

You will also develop an "ear" and "eye" for the quality of spark by the sound of the snap and brightness of the spark.

Also if you find a bad/weak module/cable combo, then change the cable with another and retest the same output of ignition module to eliminate the cable or module output.

Do not allow the cable to sit disconnect from spark plug when engine is started, that energy needs to go somewhere and will eventually punch itself thru the insulation in the module to another coil if you dont give it a path.

You'll want to disable the injector for that cylinder so you dont hydro lock it.

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On 1/17/2019 at 6:15 AM, OldSix_95 said:

I see... that one may have me stumped as well. But definitely have your car checked for exhaust damage...  had it not been for me following my gut instinct, I probably still would be trying to figure out why my car sounded and drove rough. My only issue now: finding a ride to go exchange the brand new battery that died.

Providing an update...

I took the car to a different mechanic today and after doing a bit of tinkering with the idle, checking the plugs, listening and such he drove the car with me in it. What he noticed was that the car is missing really bad. He thinks the timing is off which is causing the missing issue. He floored the gas while entering the interstate and the car put out little power. It gradually built up speed, but not straight away. I have scheduled an appointment to take the car back to his shop next week due to him being busy this week. Hopefully he will be able to resolve the issue and get my 626 back to proper running condition. I'll let you guys know the results once I get the car back.

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