Fixes for 626 rough idle, stalling

I posted the rough idle and stalling problem on mazda626.net. From the responses I got and posts from people with similar problems, I'll clean the MAF and IAC. I'll reprint my post here:

I have two problems with my 1997 626 (2.0L, ATX).

1. When I come to a stop and the transmission is still in "Drive", the engine rpms drop below 650 rpm and stumbles a little bit before recovering.

2. When I change from "Drive" to "Park" or "Neutral", the engine rpms drop below 650 rpm and usually does not recover. The engine stalls.

My current problem may be related to a transmission rebuild done earlier this year and possibly the things that I did in an auto shop class. I'll use a timeline to summarize the background.

March 2006 - Rebuilt transmission. After rebuilt, problems #1 and #2 occur intermittently.

April 2006 - Replaced battery. After replacing the battery, both problems occured regularly. I took the car back to the shop for repair under their warranty. The shop had it for several days and found nothing wrong with the transmission. They did fix the problems and told me the cause was due to a corroded ground connection. I didn't asked them where it was. I only spoke to them over the phone because this was my wife's car who was a student in another city.

Summer 2006 - Replace spark plugs, air filter, flushed coolant, checked PCV valve.

October 4, 11, 18, 25 - I'm taking an introductory auto shop class and take the car into the shop to do basic maintenance and test procedures: engine compression test, cylinder leakage test, battery load test, alternator test, measuring manifold vacuum using the PCV vacuum line, cleared CEL for "warm up cat efficiency". If anyone is interested, I blogged about the tests and results.

I've noticed problem# 1 occuring again about 1-1.5 weeks ago.

In yesterday's class, I removed the battery and the battery tray to get a better look at the "driver side upper" transmission mount. When I removed the battery tray, I saw a ground connection that didn't look original. A bundle of 4 wires came off from a thick cable assembly and all four wires were crimped together onto a single large ground lug. The connection looked a bit corroded, so I used some sandpaper to buff it a little bit.

After the class, problem #2 occured repeatedly and #1 got worse.

Is it coincidence that problems #1 and #2 are happening again or caused by something I did during the shop class? The weather has been getting colder lately.

Problem #2 seems to occur regularly whenever the battery is removed and reinstalled. Is this stalling problem due to some parameter being lost in the engine/transmission controller's memory when the battery is removed?

I did test the resistance measured between the lug and other points on the chassis, result was 0-1 ohm. I'll go back and clean up that ground connection that I disturbed in the class.


I have browsed some related threads about the engine stalling and poor idle. Most of the posts suggest to clean the MAF, IAC. I don't know if doing these things will help because it just seems that problem #2 is related to r/r the battery. Perhaps some wires inside the cable assembly got affected when I disconnected the battery cables.

Thanks for reading. I appreciate any advice to diagnose this problem. I shudder to think that it's a transmission problem again because then I have to take the car back to the transmission shop that is located 360 miles away.