i have 2 problems with my car and i have posted the 1st problem to several boards but didn't get any help, so i'm hoping someone here can help coz i'm very confused.

First, the car is a '99 SiR and the mods are: HKS super powerflow filter, aftermarket performance muffler, neuspeed lowering spring and 15" volk racing TE 37.

the problem is whenever there's a change in weather(from warm to a little less warm) the car doesn't idle properly or if i change air filter. after driving on a warm day, i decided to parked my car and not use it for 24hrs then the weather change to a little bit less warm with a threat of rain during the late afternon.when i started the car the next morning the engine is shaking and grasping for air trying to reach 1k rpm for warm up, sometimes it just stalls and i have to start the car again. after it reach 1k rpm it idles smoothly. i'm only aware of carburated engine having this problem during cold start but not EFI.

when i finally took the car to the street, i noticed that each time i decelerated while approaching an intersection, the idle drops to 500rpm and it's noticeable since the cabin becomes quiet(i'm using straight through muffler). there's one time, that every intersection i stopped at, the engine just stall and after a few km of driving it didn't happen anymore but the dropping to 500rpm still happens up to now and it's getting on my nerves.

sometimes by taking out the air filter and replacing it again also results in those problems. i didn't touch anything, like timing and etc., after those mods i just resetted the ecu. that's all and i know it shouldn't have this kind of problem.

i didn't take it to a dealership or mechanic coz most mechanics inluding those of the dealership are not competent enough(in this country) to troubleshoot such problem unless there's a part(s) that's broken. they'll just guess and recommend this and that part for replacement but still doesn't fix the problem. by the way, we have a tropical climate here with high humidity.

my questions are:
-is there any serious problem about my car?
-have anyone experienced this, maybe on other cars aside from SiRs?
-is there any fix to this?
-will it harm performance?

SECOND, i have a custom made cold air intake and this morning i passed by a very flooded street and completely forgetting that i have a cold air. then the engine just stalled and i have to pay some people to push it out. i tried to start it but it won't crank just clicking sound from the starter and i waited for a while and tried it again, this time it started after a long cranking. but when i hold the rev at 3k i can hear succesive popping sound and when i let go of the gas the engine stalls. when it finally started easily the idle is about 600rpm and you can't drive it far since it stalls after decelarating and that's when i decide to check my filter which was soaking wet. the car also hesitates at 2k rpm and sounded like a harley bike but when it reaches 3k it sounded normal again and drives ok. now my questions are:
-is there a chance that water got into the combustion chamber or is it air not passing through the filter coz it's wet and resulting in hardstarting?
-what are the problems of water getting in the chamber? will it burn away or will it cause any serious problems?
-is there anything i should check or just wait for a problem to arise?
-what causes the succesive popping sound and why did it sounded like a harley under 3k rpm?

now i'm at work and i don't know if it will still continue to act silly later when i get home. hope not.

i hope somebody can help me with these problem especially the 1st problem.

Thanks very much in advance.

 

Are you getting any codes? That could be a lot of things. The problem with these cars is that sometimes you just have to throw parts at them until you figure out the problem. You can do a couple of simple tests like check for vacuum leaks, and check for a sticking injector. You can use a stethoscope when the car is idling and listen for a clicking noise. What you have doesn't sound like an ignition problem, so concentrate on air/fuel. Have you tried swapping air filters? Maybe try a new fuel filter.
Right now, I would be worried how much damage you did when you hit the water. Do a compression test right away and see what you come up with. In case you don't know how www.c-speedracing.com has a how-to on it.