When my miata is cold...: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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April 27, 2010 5:13 p.m. bigbrainonbrad New Reader

When I first start the car (91 Miata) in the morning, between 1500 and 3000 rpms, the car feels like it is pulling a LOT of timing, to the point where there is a buck and feels like it is backfiring. Load does not seem to have an effect on this condition. Once the revs get high enough the problem goes away and the car drives normal. Car is completely stock, timing is set at approximately 14 degrees and runs fine on 89. I replaced the plugs thinking that maybe they were extremely worn, but looked good. Plug wires are in good shape too.

In short, car idles fine, feels weird between 1500 and 3000, fine otherwise. Seems to be in overall good mechanical condition.

Thanks in advance
April 27, 2010 5:43 p.m. Don49 New Reader

Check for an intake leak. I had similar symptoms with my Toyota and there was a crack where the intake connected to the plenum.
April 27, 2010 5:55 p.m. Keith SuperDork

Possibly a dead spot in the AFM, but I'd expect that to persist after warmup.
April 28, 2010 5:23 a.m. foxtrapper SuperDork

Well, put a timing light on it and see. I rather doubt that is the problem. But a timing light will let you know.

I also suspect a vacuum leak.
April 28, 2010 9:08 a.m. Powar Dork

Sounds exactly like what my old '90 did when the crank snout was dying.

I guess it allowed it to jump timing.
April 28, 2010 2:10 p.m. bigbrainonbrad New Reader

Update

Today it was a bit warmer and when I started the car it ran fine. When this problem has presented itself the temperature had been in the 40s or low 50s. Possibly unrelated but, when the weather was much colder when just started the cel would come on for a minute or so. The car would run fine though.

I'm thinking that some type of intake temperature sensor is going bad. If the sensor is reading wrong the timing or fuel curves would be wrong.

Not knowing anything really about the vane air stuff, is there something that meters air temperature? I have a MSPNP ready to go in but have not had the time to do the work,I would really like to be able to drive this car in the meantime.
April 28, 2010 2:36 p.m. MCarp22 Reader

My miata has similar cold symptoms, but i figured it was the untuned rx-7 airflow meter.
April 28, 2010 2:36 p.m. Powar Dork

What was the CEL code?
April 28, 2010 2:52 p.m. foxtrapper SuperDork

Happened to run across this thread, which might have some bearing with regards to your symptoms.

http://forum.miata.net/vb/showthread.php?t=361607#post4284826
April 28, 2010 3:33 p.m. Keith SuperDork

bigbrainonbrad wrote:

Not knowing anything really about the vane air stuff, is there something that meters air temperature? I have a MSPNP ready to go in but have not had the time to do the work,I would really like to be able to drive this car in the meantime.

Yes, there is an air temperature sensor in the air flow meter.