Yes I understand that topics like this are posted constantly, but my problem is a little different (what problem isn't?). I own a 1995 Mazda 323 Protege with a 1.8L DOHC engine. Recently I found a crack in the manifold and sent it in to replace the old one. Well, after it came out of the shop I drove it for a while. Soon I noticed that when i was in neutral (or clutch in) the idle RPM was closer to 1000 than the usual 750. Then it started to randomly rev itself up to 2000rpm then drop back to 1000ish. It does this every few seconds. What I don't get is it was running fine before I sent it in so it cant be a dirty MAF. So is something not connected right or what?? thanks

 

Sounds like you have vacume leak. Check for a lose/damaged vacume hose and air intake hose for cracks. Especially check the plastic tubing after MAF.

If the repair was done in the inlet manifold, then there is a possibility of leaking manifold gaskit packing. You cannot reuse gaskits.

 

Repair was done on exhaust not intake manifold.

After looking very carefully at the engine (although I know very little about where things are) I noticed that the clamp on the end of the air intake hose that goes into the throttle body was loose as. Tightened it and then noticed a small crack at the end of the air hose that goes into the top of the engine (top right of block in pic). sealed em. Ran the car around for a while and when i got back I parked and left the engine running. It seemed that the rpm fluctuated less often than last time but it still every few seconds would shoot from 750 to 1000. This happened when the cooling fan turned on I think. Then after a lil longer it went to 2000 and back again. Happened around once every 10 sec. Sometimes it didnt do anything at all. Checked all electrics to see if it was that, but there was no difference with all on and all off.

So I'm thinking, is the computer that controls mixture at idle going nuts, or are there more leaks I may have missed. If there are more places I should check, could you please tell me exactly where to find them

Thanks for all your help. Here is a pic of the engine bay.

 

Okay, Since you have changed the exhaust manifold, there are two things you have to look in to. First is O2 Sensor. Check to see is there any damage and for the proper electrical connections. Second is the metal pipe starting from the exhaust and runing back side of the engine near the throttle body. This is for the EGR (exhaust gas recirculation) valve. Check every thing is reinstalled properly. You may need experienced techs (friend) support at this moment. If you don't know what is EGR, look in to this thread.

http://www.msprotege.com/forum/showthread.php?t=94788

Before you go any further, you can reset the ECM by disconnecting the (-) battery teminal for 10 min. You may have to rest the channels on your radio after this. Once you reset the ECM, it will start running on factory settings. If you have OBD II ECM, it may take 50km of driving to learn and record new fuel trim.

 

how do i tell which ecm I have? either way, i dusted out the O2 sensor plugs, and tommorow I will give it a good long drive. If that does nothing, ill come back and do the battery thing. I really don't have the knowledge or mech minded friends to fiddle with the EGR, plus the thread was for the 2.0L engine. Is it the same for my 1.8L?

Thanks for all the help so far. Hopefully this won't result in me spening money at a mechanic

 

after driving about 30km's today (so totalled around 50 since service), and changing the airfilter, the car stopped its crazy idle revving. I think that it must have now learned its proper fuel managment. THANKS FOR ALL THE HELP!!!!!! and now back to driving