Not wanting to idle smoothly

[zoomtictac]

Last night I decided to bump up the timing and see what would happen with a cone filter in place of the airbox. The timing bump went fine I guess, although I was really disappointed to find out that the car was already set to 16deg advanced! No wonder the car felt so strong. It's kind of strange to me that the dealership wouldn't have checked something like that - or if they did, that they would LEAVE or SET it that way. Also kinda surprised that I had no problems on 87 fuel. I set it back to 10 and took it for a drive, and then bumped it back up to 18 degrees. Ran fine.

ANYWAY, I wrestled around with the airbox for a while, finally got that off, and then wrestled even more with an adapter and cone filter I had sitting around. Apparently rubber doesn't like to move or stretch in 45degree weather... FINALLY got that on and took it for a drive, but every time I pushed in the clutch while coming to a stop, the idle would droop, almost stalling, and then correct itself - over and over and over. I got back to the house and parked it, just sitting in neutral watching the rpms, and it kept doing this the whole time, although by the time I turned it off, it wasn't near as bad as earlier. It still wasn't idling smoothly though.

Any ideas? Can I simply fix this by jumping Gnd and Ten and adjusting the screw on the TB?

[jamaican]

maybe when you wrestled the intake hose that caused a vaccuum leak

[Clean 4WD]

I would do like jamaican said and look at the intake hose for any leaks.. but yes you can jump the ten/grnd connectors and adjust the idle.. side not you should jump those as well to adj the timing..

[Jho]

Like previously mentioned, check for vacuum leaks, also check your VAF plug, or anything else you might have touched.

[zoomtictac]

I'm not exactly sure where to check for leaks.. I left the H-box (I think that's what its called?) in line behind the AFM, the tube that gets attached to it is still attached, the AFM plug got plugged back in, the crankcase breather line is still attached... I'm not sure there's much left. I guess I'll make sure the AFM plug is tight, but I've accidentally left it unplugged before, and the car ran like total crap - kinda like bad injectors do - stumbling and barely keeping idle, hesitating under light throttle, bogging and threatening to stall under medium or heavy throttle. It's really not that bad right now. Normally it idles around 750ish, and now it kinda dips to 500, and then jumps back up to 900-1000 like its compensating for the dip, settles back to 750, dips to 500... etc. This all happens within 1.5-2 seconds.

And yes, I jumped the connections while setting the timing - I've done it several times on the Miata, so its getting pretty routine..

Any spots on the intake tract that I missed? Other ideas (crappy filter, something wrong with ignition system at the current timing maybe, etc)?

[naprotejay]

cracked intake tube? if its the stock original intake tube, I almost guarantee you that's its cracked in the 'pleated' section if so, you can use some duct-tape to seal it back up.

[jamaican]

we had to jump ten and gnd to advance timing? i didn't do that, i just un bolted both screws and then checked it with a gun... heck, im so good i can jump out my car and change the timing at a red light

[zoomtictac]

Not sure about any cracks - I double checked all the connections again tonight, and everything looked to be securely in place. But, it was the middle of the night, and the only light I had was a floodlight on the garage and a mini maglight. I'll have to check the intake tract again tomorrow during the day. I just can't get over the fact that this started happening after replacing the airbox with the cone filter - its almost like the filter is keeping the engine from being able to do something, or giving it more of something than it can handle. It may sound ridiculous, I know, but if I could explain it better or be more specific, I'd know how to fix the problem, now wouldn't I??

Well, after checking all that, I was playing around with the timing some more tonight, trying different settings, and taking each one for a quick drive. Previously, I automatically took it to 18deg, because I knew that some had dyno'd and found that 18 yielded the best gains. But after feeling the other settings, I think I've found that I like 14 the best. It shifts the torque curve a little higher into the midrange (as compared to 18), which results in an extraordinarily strong surge when the powerband is reached. Which I likey. I would imagine that the shifted torque curve also attributes to the feeling that the power doesn't seem to drop off at all above 6000rpm, which wasn't the case when I had it set at 18. Makes it great fun to drive.

[jamaican]

try simply tightening all the screws between the trottle body and the AFM... like where the hose bolts to throttle body, h-box, check the little breather hose too... sometimes just by moving around the intake hose things become lose etc.

[Jho]

we had to jump ten and gnd to advance timing? i didn't do that, i just un bolted both screws and then checked it with a gun... heck, im so good i can jump out my car and change the timing at a red light

Yeah, you're supposed to put the car in "base timing mode" before you adjust the timing.

[jamaican]

Yeah, you're supposed to put the car in "base timing mode" before you adjust the timing.

and what if i didn't?

[zoomtictac]

Then your computer is probably trying to compensate for the change you made. If you don't "tell" the ECU that you're going to be changing something, its going to assume that something is wrong if things are not exactly like it expects. I wouldn't be surprised if your car was running worse after doing that.

[zoomtictac]

By the way, the idle problem seems to have disappeared. Car is running great.