'91 Si(2.1) starting/stall problem -- ECU codes

Hi everyone. I know I'm fairly new here, but I've got a question.

I bought this '91 lude, AT, with about 190k on it. It seemed to run fine at the time -- needing a tune-up and an oil change. Well, I got the oil changed, and I've been putting off the tune-up. Anyway, I don't think that's related. As it's gotten colder(nights ~40 degrees) the car has become hard to start in the mornings. When you turn it over, it doesn't idle high, it crashes and stalls in a couple seconds. If you gas it for awhile and let it warm up, it's fine, but the S3 light usually blinks indicating a speed sensor problem, but the '91s have electronic sensors, no? The ECU is also throwing a code 10(Intake Air Temperature Sensor) and once it threw a code 41(Oxygen sensor heater.) Once it's warm and you restart it it's fine, but that first start is always scary, especially for my mechanically-deficient fiancee. What's going on? Should I replace the IAT along with the plugs/wires/rotors and see if that works? Is that even the problem? How hard is that to replace on the 3rd gens. Anyone?

-James

Ok if im not mistaken, what your iat does is this. I reads what the temp of the air is, and tells the comp whether or not to take outside air into the intake, or simply recirculate the already heating air. If this sensor was bad and telling it to take outside (cool) air in, then that might very well cause your car to violently shake around then die. I am carbureted though and have a choke also, but that sounds like it's a good place to start looking. One easy way to check, would be to look at your manifold and see if it's sucking outide air in. ( on my car a vaccum line opens a slide and it's easy to see, i don't know about yours, but I do have an 84-95 prelude chilton and could look if u tell me the year etc. Let me know. Hope this helps.

-Bob-

PS the oxygen sensor code could very easily be related to the bigger problem which I think is the iat sensor. That has been my experience. Once one thing idn workin right nuthin does.

Heres what chilton says,

Turn the ignition off.
Remove the clock fuse in the relay box for 10 sec. to reset ecu codes.
Turn the ignition switch on.
Is the check engine light on.
IF NO=Intermitten failure may be occuring. Check for poor connections or loose wires at ta sensor and c235 located at right shock tower.
IF YES=Turn the ignition switch off.
Disconnect the 2p connector from the ta sensor.
Measure the resistance between the 2 terminals on the ta sensor.
Is there 1-4k ohms?
IF NO=replace the ta sensor.
IF YES=Turn ignition switch on.
Measure voltage between the white/red terminal and a body ground.
is there approximately 5volts?
IF NO=Repair the short of replace with a good ecu and retest.
IF YES=Substitute a good ecu and retest. If the symptom goes away, replace the original ecu.

Hope this helps, I gotta work on my car now, and That took me a while anyway so good night to me.

-Bob-

Sweet.. thanks for typing that out. Actually, I just read something similar in the online shop manual.. so.. sounds like a plan. This does sound like it could be the issue.. so I"ll bust out my meter tomorrow and test it out. What's the best place to get a new one and how much am I looking at? the symptom you described is exactly what i'm experiencing with the shaking... so I think I've got it pinned down now.

-J

To tell you the truth, I don't know what they cost. Call around to local parts stores and check online and compare costs and time to get the part etc. This MAY not be your problem, but reason would say that it IS the best place to start. Remember, think like a computer.(ecu) They Aint smort liake us is. Theys stuped.

Well, I've found a temporary fix(I think) The cold start thing is NOT working, and I've got about a week before my next paycheck comes in. So I'm going to try to wire a simple resistor up and see if I can trick it into thinking it's about 50 degrees. I'll lose some performance, but it SHOULD start, no?

-J

I don't know. I don't think I would try it, but it's your car. Did you run those tests? What was the outcome? Did you look to see if on you air intake you have a vacuum line connected to a open/shut door thing? Let me know as quickly as possible please.

I really wouldn't do that though. It's too risky. Unless you hate your car and are willing to part with it.

Well, the schematic showed the sensor as a variable resistor, so, I was willing to try. IN short: it worked, but I ended up not leaving it in permantently, because I didn't want the resistor burning up or something else happening. Anyway, when I did, the code 41(o2 sensor heater) came back on the right LED, and the left one went away. Sounds like they're both bad. *sigh* well... it needs a tune-up anyway, so payday will mean a trip to autozone for me. Any suggestions on plugs? i've heard NGKs are the best in these, but, that's just what i've heard... lol.

-J

*bump* Any other Ideas?

-J