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Another surging idle, with some experimental results 200 1991

posted by  mdouma on  Wed Apr 12 04:01 CST 2006
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last visit: Fri Oct 18 15:10 CST 2013
[RELATED]

I have to take my 91 245 to the Drive Clean emission tester soon, but I'm still plagued with a surging idle, 1000 to 1500 and back, and the little gauge I built to display O2 sensor voltage reads very low, except for a few seconds after I let of the gas, or when I disconnect the FPR and plug that vacuum line. In the latter case the gauge shows normal, if a bit slow, up-down voltage like I was used to having. I searched for a vacuum leak, cleaned the throttle body (twice, the first time was 6 months ago or so, and may well have started this whole episode), and replaced the FPR and O2 sensor.

If I disconnect the IAC, the idle drops to a nice idle, if a bit low, and I can reconnect it, and the idle stays down until I re-start. Throttle switch seems to work (disconnected and both IAC hoses, and TPS, rotated IAC so I could see the valve, re-started, and watched the valve slowly open when I shorted pins 1 and 2 at the TPS switch).

Problem is, as I see it, the valve never closes under normal conditions, hence my continuously lean burn. Drivability and fuel economy are good, and no knocking. Error codes are 221,231, and of course, 223. Is this a IAC problem, or is the computer stuffed? Any opinions? TIA

Marten





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