2001 NB stalling out and surging RPMs, no power after long drives

I am having an issue where after a long drive, my 2001 LS stutters and then becomes un-driveable for a few hours, due to the engine dipping down to 300 RPM and then "surging" up into the thousands of RPM rhythmically..

I paid for an oil change (yeah, yeah), changed the air filter, and drove to Tulsa, but only made it 2.5 hours north. When I came to a stop light, the engine stalled. After restarting, the RPMs started surging and stalling rhythmically, no power, engine running rough. No CEL and no codes pending. After 2 hours of rest and a disconnected battery, started up and drove it to Tulsa. Rested a week. Drove back to Dallas and it broke down on me again in the same way as I hit town.

I have changed the air filter, checked the throttle body for obstructions, cleaned off electrical contacts to the MAS/CAS, and changed the fuel filter. No check engine light and never had any engine problems at all. Car has 75000 on it.

Thinking I might be the CAS. Does anyone have experience with this issue or some way to diagnose it ?

Camshaft position sensor would be my guess had to replace on on my '02 with similar symptoms :

http://forum.miata.net/vb/attachment...chmentid=60737

POS Racing were you having the issue only when the engine was hot? Summer is coming...

Yep she would run like a champ up until it hit the magic temperature. It is a known failure item on the '01+ Miatas but thankfully its not a high dollar part.

YMMV

I've also had to replace the coil packs on our '02 when they went bad it would run like crap like it was running on 2 cylinders (because it was running on 2 cylinders).

Do you have an OBDII code reader? They're pretty cheap and can help point you in the right direction. Pep Boys or similar can pull your codes too, but, of course, they'll be anxious to "help" you fix it.

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Originally Posted by cwisenheimer

Do you have an OBDII code reader? They're pretty cheap and can help point you in the right direction. Pep Boys or similar can pull your codes too, but, of course, they'll be anxious to "help" you fix it.

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Good advise! I got an OBDII scanner just for problems like these!

I have an El Cheapo model code reader. I got no CEL, no faults, and no faults pending, even when the engine is running like crap and stalling out. Is this something to expect if it was the CAS?

I also wonder if there's a way to test the CAS out of the car. I have an oscilloscope and other such fun toys.

Go buy a new one and if it runs better you are fixed. ;-)

Without a code everyone will just be guessing anyhow so fire up the parts cannon! ::Banana::

http://i.imgur.com/SzALe.png

POS Racing, Yup, ordered. Problem is I don't really feel like breaking down in the middle of Oklahoma again...

Do you remember if yours was throwing a code?

Its posted here somewhere I'll do some diggin.

When I ordered CPS I got 2 one is hanging on the workbench. ;-)

CPS or CAS? Hmm.. I see two things.. a CPS and a CAS. The CPS (crankshaft position sensor) is the long one in the front of the valve cover, mounted horizontally. The CAS (camshaft angle sensor) is the short one in the rear of the valve cover, near the firewall, mounted vertically. I loosened the CAS a little and sure enough, car wouldn't start :P.

Easy way to test it. Pull the sensor out and dip it into a cup of cool water for a few minutes. Pop it back in while the motor is still hot. If it is the sensor, it will run fine again. Many folks keep a spare in the glove box, as it is a known issue with old sensors.

The sensor in the valve cover called the Camshaft Position Sensor (CPS).

The code was 1345 I believe.

Thanks everyone! I feel like I at least know what to look for next time it happens. Can't wait for 100 degree days.

Same thing happened to me (on 114 on the way back from an autocross. CPS. Easy fix. Pain in the ass to deal with though.

Had the same problem. It eventually started throwing the cam position sensor CEL. That was not the problem. The wiring from the crank position sensor was rubbing against one of the accessory belts and had worn through the insulation. It was shorting out the crank position sensor. That harness routing is tight around the belts.