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Jim Barlogio
Jim Barlogio, ASE Certified Technician
Category: Car
Satisfied Customers: 1257
Experience:  38 years Import and Domestic
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97 Miata: It idles really rough, but never stalls out

Customer Question


I just got a '97 Miata passed down to me from a family friend. Unfortunately, it was given to me because there were issues that arose with it last month. It idles really rough, but never stalls out. It sounds really angry too, like a grumbling v8??? I only drove it from their house to mine. I had the CEL read:

P1170 -- HO2S.
P0430 -- Catalyst efficiency below threshold.
P0302 -- Cylinder 2 misfire detected.

I was told that the timing belt and water pump was replaced a week or two before all of this started to happen.

I first thing I did was swap out the spark plugs and wires. Nothing changed. I'm going replace the catalytic converter. Anyone know which heated o2 sensor this code is for?

I really like the car and would like to keep it. Any assistance would be greatly appreciated. Thanks.
Submitted: 7 years ago.
Category: Car
Expert:  Jim Barlogio replied 7 years ago.
First thing is to be sure the timing belt was installed correctly. If it is off one tooth you can get a misfire code. One quick way is to hook up a vacuum gauge: @ idle you need to see a minimum of 17 inches of vacuum. If not then I would check igniton timing, then the timing belt marks. It may be off one tooth and that is all it takes.

PO1170 : Front oxy sensor heater: they do fail.. LOCATION #7

1. Timing belt must be dead on
2. Check ignition timing and engine vacuum
3. Replace front Oxy Sensor
4. Cat failure: temp in should be 100 deg min less that temp out.. We use a thermal infrared gun to check this.
5. If misfire is still in # XXXXX then need to check engine compression : needs to be over 125 lbs.
This should get you on your way.... Jim B

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Jim Barlogio and 6 other Car Specialists are ready to help you
Customer: replied 7 years ago.
Thank you. Would the cylinder 2 misfire cause my car to idle so rough? Sometimes it feels like it wants to shake its way out. Would the timing belt issue be the cause of only one cylinder misfire or multiple if it was off by a tooth?
Expert:  Jim Barlogio replied 7 years ago.
Is the miss constant... Any other codes? There have been problem with the coil packs also. Need to see if spark is constant to that cylinder. Compression good. Timing belt on the marks.. Best way to find a problem is go down a check list,, if you start skipping around you can miss the problem.

Vacuum leaks
Timing belt marks

I will check back with you.. JB
Customer: replied 7 years ago.
The miss is constant. I had the car compression tested -- good, vacuum leak tested -- good. The coil was tested and is good. No other codes but the P1170 and P0430 -- which is I what I believe to be caused by the misfire.

UPDATE -- I pulled the plug wire from all 4 cylinders. There was hesitation when I pulled the plug wire for cylinders 1,3,4... but nothing changed when I pulled the plug for cylinder 2. I am getting spark. I can hear the injector engage with a click. Can the fuel injector just be clogged? Should this give me a CEL for the injector? Would bad timing somehow caused this? I will double check timing again but it looked spot on... Sorry for all the questions...
Expert:  Jim Barlogio replied 7 years ago.
Good morning,
Yes the injector can be plugged. If you have compression, spark , no vacuum leak on that cylinder then fuel is the last thing. Try swaping the injectors and see if the miss moves. One last thing is to check the egr valve and make sure it is not stuck open.

I will check back. JIM