Idle Issue

BlitzxCraig

Member
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Mazda Proteg5
Hello everyone! This is my first post. I am posting here as I have done extensive research about an idling problem I've been having but I can't seem to find anything to match my problem exactly.

So here's the problem- when I start my MP5 cold, the rpms go up to 1500-2000, which is normal for a cold start. They gradually go down to normal operation rpm-about 700-800. However, every now and then, it will drop to almost 100, then jump right up to about 1000 then back to 800. Usually it stops there and runs normally and continues to run normally throughout the day. One time, it did that after I filled it up, and it continued to drop and go back to baseline rpm over and over. Then today, I started it and let it idle to operating temp with no symptoms, but then it suddenly dropped worse than ever before and nearly stalled and the battery dash light came on. It has 148k on it, and I know the plugs and wires were done by PO.

I know that Proteges have common problems with MAF sensors and EGRs, IACV, etc., but I have no check engine light on. I was under the impression that those almost always throw a CEL. Because it happened after a fill-up, I was wondering if it could be a fuel pump problem. Also-the car has no problems with acceleration or mileage, and it has never done the idling thing at stoplights-only when first started, and even then it is intermittent. I am planning on cleaning the MAF sensor and possibly the EGR, and checking vacuum lines. Any other suggestions?

Thanks in advance!
Matthew
 
I recently had the same exact symptoms on my MP3 and it was the MAF and no CEL was on I replaced it with a spare I happened to have and it's been perfect since.
 
I think you should try a can of seafoam.

Half a can in the gas... Half a can up the brake booster...

I sea foam my car as soon as my idle starts to stumble.
 
Thanks for the suggestions! Research is great and helpful, but it's always nice to have some direct suggestions from those who have experienced it before.
 
I say try cleaning the MAFS first, use CRC MAFS cleaner found in most auto parts stores. After cleaning the MAFS it is a good idea to reset the ECU by disconnecting the car battery for a few minutes.
 
If you reset the ECU the car will have to relearn how to idle... it will run like crap and nearly stall while it learns.

If your car already idles like crap it may get worse.
 
See, it actually idles beautifully most of the time. That's what makes my problem so frustrating. It does it at seemingly random times. But I'll keep that in mind, thanks!
 
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