Bad idle on '91 626

A 'searching idle' is commonly cured by a slight fuel/air idle mixture adjustment. Not familiar with this model as to adjustment screw or components that affect this. rick

There should NOT be zillions of vacuum lines unless somehow mazda slipped you an engine from the late 70's.

There should be less than a half dozen actuall vacuum lines. Stuff like the brake power unit, the idle air manifold, and the cruise control actuator. Start at the intake manifold and look for stuff coming off it.

Does the ECU report any errors? Is your ignition system perfect -- nice fat spark if you pull a wire and hold it 1/4-1/3" from a ground? Timing correct?

Don't replace anything unless you've actually tested it bad. One mistake will easily cost you more than having a mechanic diagnose the problem.

I very common failure with these (I own a 91 626 and I'm also a mechanic), is small cracks in the intake air hose. These are very hard to see without removing the hose. I fixed mine by wrapping the entire hose with 2 layers of electrical tape.

Larry

===============Well, I'm kind of an old-timer. More than one going to the distributor (and in the really old days, one going to the wipers) kind of throws me. ===============

===============No errors show on the dash, but I don't think it is equipped to do that. Doesn't seem to have a "Check Engine" light or whatever.

Is there a port to plug into with a relatively affordable unit to read out such codes? I could use a hint like that. ==============

Is your ignition system perfect -- nice fat

=============Timing is dead-on. Plugs are new within three months. Cap and rotor new. Wires could be questionable. Filters are good. Haven't checked spark, but will on Saturday, if the weather is bearable. ============

===========I only meant that, if this is a textbook case of the symptoms of some particular failed control, part that I would be willing to roll the dice. No, I don't want to go replacing bushels of parts on a whim.

PLEASE NOTE that the idle only goes silly when the car is in DRIVE. Not Park, not neutral, and not even when it is in REVERSE. This seems kind of odd to me.

Thanks for any help you can offer,

Hamish

Original Post Below:

ECU nowadays. Did a '91 vehicle really have a vacuum advance? I'd be amazed if that was really true.

An ECU will often have errors to report without lighting the check-engine light. There's usually a procedure like flipping a switch and then turning the ignition on, or doing something wierd like turning the ignition on then off 3 times within 10 seconds.

their business to do so. Autozone for example.

...

I did mine with duct tape. Take the intake "boot" off and inspect by flexing it. Cracks do not appear in the "valleys" but do on the "peaks" on mine.

Al