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Date: 20 Oct 2002 15:06:53 +0300
From: Simo Melenius <siolnanopsamfi>
Subject: 900i16v and rough idle -- AIC-valve suspected


Hi! If you're a technical guy/gal and enjoy problem-solving and detailed analysis, please read forward if you have the time. This is a long message since I started writing I thought it's better not to stop until I've said anything I have to say. :) I've been observing my 900i16v (-90, 235tkm) for a few months now; it occasionally suffers from rough idle (from minor RPM shaking to jumping RPM between 500-1300, yikes!) that also affects when releasing the gas pedal while driving, e.g. when slowing down for redlights in time. In other words, it happens when the throttle plate is closed; the engine works perfectly when accelerating/loading the engine. The idle becomes rough especially during cold/rainy days, it ran 90% OK during the dry summer time. Now we've had nightly frosts here in Finland and some dampness probably gets into the engine since I keep the car outdoors. Sometimes it happens that the engine actually works almost perfectly for a short while eventhough it had just failed to maintain a constant idle a few minutes earlier. How rare is it for an AIC-valve to break and is there anything I could do to check it's fully functional? *** The resistance of the AIC-valve terminals is within the specified range and the voltage to the harness connector is exact battery voltage when unplugged, as it should be. The LH2.4 self-test audibly clicks the AIC-valve open/closed as programmed, and I can feel the clicks with fingers. However, the engine still runs rough when idle and the only thing I've noticed that helps is lubricating the AIC-valve: this effect lasts for few days only. Due to the good test values for AIC-valve, I've also inspected other parts of the fuel injection system and ignition system: everything I've tested is OK: ignition wirings/voltage/spark is good, fuel supply and pressure is good. Oxygen sensor works and I get perfect exhaust gas values. Throttle plate sensor OK, temperature sensors OK. No intake air leaks as far as I've investigated. The LH error codes I get say overly lean/rich mixture, oxygen sensor self-compensation failure, AIC-valve self-compensation failure. I don't have the list of codes here with me now but they all indicate too much air or fuel and hence, a LH component failing to work correctly. For a while, I suspected a corroded wiring/connectors but my local mechanic didn't find anything obvious either when I asked him to look around for a couple of hours during the last maintenance service. What's the supposed voltage to the AIC-valve while connected and running, I get 2.5-3.5V most of the time? Should it be 12V -> fully open and 0V -> fully closed (mechanic limp-home idle setting) and anything between those (or 2-3V - 12V) for normal operation? So I'm back to the AIC-valve. I'm going to see my local Saab scrapper and ask if he'd lend me another AIC-valve for testing. The lubrication would suggest that it's the valve: I've noticed CRC helps for a few hours and some thicker oil helps for a few days. I certainly hope it's the valve, otherwise I'm completely clueless. I'd appreciate that you'd post a follow-up to this message if you have any comments. thanks in advance, Simo Melenius -- 0110011001101111011011110110001001100001011100100010110101110000

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