I've read about 1 bazillion posts on rough idle but haven't been able to resolve mine. It started about a month ago and has gotten progressively worse.

Symptoms: Idles smooth at 700-1000rpm while in park, a/c off. Turn on the a/c, idle drops slightly (that's normal) then gets erratic. It never goes high, just random hard drops, a couple times a second, almost to stall. Turn a/c off, goes back smooth. Now put it in Reverse or Drive, same erratic idle. Park or neutral, smooth. Drive + a/c is worse that either by itself. No CELs. Alternator is charging properly. When driving, it sputters off idle but gets completely smooth by 2000rpm. The symptoms aren't there on cold start; they start showing up after running a few minutes.

What I've done: Removed and cleaned EGR valve, IAC, and throttle body with carb spray. Carbon was fairly light for 150k miles and the EGR moved pretty freely when I took it off, so didn't think cleaning would make much difference, and it didn't at all. Cleaned MAF with MAF cleaner. It was pretty clean too, and no change. With engine at smooth idle I sprayed carb spray at every hose and connection I could find, nothing blipped. I cleaned the engine ground strap and battery terminals; they were clean to start with. Replaced gas cap. Replaced coils, plugs, wires. Replaced air intake 2 years go. Threatened to drive it off bridge or into tree. Let it idle both with and without PCV valve plugged in, no change. Idled with EGR both connected and not, no change. Idled with IAC connected and not. It wouldn't idle on it's own, but could hold it at idle by the gas pedal and still got the same symptoms. Threatened to drive into a bridge. Nothing has helped.

Somebody, anybody, ideas?

Thanks!

 

Did you spray carb cleaner all around the intake manifold gasket?

 

Not yet. Ever heard of that being a problem with a Protege?

 

Seen intake gaskets fail on older Mazda's before. Very common on 626's.

 

Ever get this problem resolved? I have a similar problem on my 98 626 and this is the most relevant thing I've come across:

https://mazda626.net/topic/30382-iac...comment-257594

 

Yes. Had to replace both ignition coils, twice. I initially put one new one on and the problem remained. So I swapped the old ones and the problem remained. So then replaced the old coil with a new one (so now both new) and the problem remained. Pulled my hair out for weeks, ended up taking to a shop. He hooked it to the machine, said bad coils. I told him now way, they were both new. I told him I had replaced them one at a time, he said adding a new one to a bad one could jack the new one. Once the first new one was jacked, the second one then got jacked by the now-bad first one. He replaced both, has run perfect ever since. I'll never do a single coil again, always in sets.