i am having a very interesting idle issue. the engine seems to have a "miss" when at idle and under light load. its almost like an injector is misfiring, but the misfire disappears when i get over 3800rpms.

i checked the timing, afm, pressure sensor, vacuum leaks, tried switching the primary injector plugs around, made sure the plug wires were hooked up right, just about everything...

where do i go next? one of my biggest pet pieves is a rough idle and i cant get it to go away

 

I would say check you TID for cracks.....I had a really rough idle that could not be fixed......then I say that the TID had cracks all over.....I'm not sure if you have the stock or aluminum....I assume aluminum. Good luck.

 

custom TID. the engine is pulling great vacuum so i dont think its a vacuum leak.

 

Maybe fouled(sp?) plugs?

 

ground maybe

 

.....

 

o2 sensor, wires, plugs, fuel filter.

if its not a ground it might be a loose electrical connection to ignition coils, have a problem like that on my talon, low rpms and light load the car runs like absolute crap, because it has a sketchy connector to the 3-4 coil pack, as the rpms increase and heavier load and the signal becomes more frequent (more powerful too maybe?) it runs great.

 

I would guess a primary injector is either dirty or has a poor electrical connection. Since the engine runs on only the primary injectors below 3800rpm, any problem with one of them would be far more obvious below that.

 

have you REALLY checked for vacuum leaks. try the starting fluid method. if you don't know it, buy starting fluid (peak $0.99) spray it near vacuum lines and places that a vacuum leak could occur. if the idle raises just for a moment where you sprayed it, start looking for the vacuum leak.

 

yes.

i have two vacuum lines:
#1 BOV/FPR/boost gauge/boost sensor line
#2 the oil injectors line.

 

yeah i thought this myself so i took out the injectors and switched the primaries with the secondaries. started it back up and nothing changed, so that can be ruled out now.

 

There are plenty of other places to have a vac leak. Every single inlet tract connection between the AFM and the engine can leak and cause your symptoms. Good manifold vacuum doesn't discount pre-TB vac leaks. Make sure the clamps on your TID are tight.

Are you sure the problem stops at exactly 3800rpm? If it does, then it's likely it's related to the primary injectors, even if it's not the injectors themselves. Perhaps a grounding issue?

BTW, I wouldn't recommend having so many things attached to one vac nipple. The FPR in particular should be hooked up to the nipple the Mazda used, the angled one on the inside of the LIM.

 

hrm... when I bought my TII(rip) I noticed that the car would do that when cold... the previous owner had not changed the air filter in a while and the rubber seal had broken down and dripped into the AFM causing it to stick until the car had warmed up and liquified the goo. I cleaned it out and that fixed it.

 

no it doesnt excactly remedy at 3800rpms, its more gradual. but the problem goes away around 3000 rpms or so. i was very careful blocking off all the vacuum nipples and such, and even rechecked them all last night to make sure, and made sure my LIM>UIM gasket was good. i'm am fairly certain its not a vacuum leak, but its still a possibility.

this is driving me crazy.

 

IGNITER? CHECK BOTH TRAILING AND LEADING!!!!