'98 V6 Rough Idle

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Today 10:34 AM
RHF52 (http://www.automotiveforums.com/vbulletin/member.php?u=576145)

My '98 V6 4-Runner idles roughly when AC compressor loads up. Stops when compressor unloads. Vacuum leak? Where? Thanks.

If everything is operating normally, except for this problem, to me it sounds like your engine is not getting the signal to idle higher to compensate for the drain caused by compressor operation.

Most likely it is one of two possible problems. One is a malfunction in your compressor circuit and the other is in the A/C control assembly.

See inspection procedures on pages DI-632 and IN-28 in the Toyota Service Manual.

If you don't have one, let me know and I'll send you a link. The troubleshooting procedure is too complicated to easily relate to you here.

The rough idle is at 750-800 RPM and occurs whether the compressor is loaded or not. Though I don't get any trouble codes, I suspect the oxygen sensor(s). They have never been replaced and I have 230K on the vehicle.

If you want to replace a Air/Fuel Ratio sensor, replace the one nearest the exhaust manifold (Sensor 1). The HO2 sensor behind the cat converter does not control the engine operation.

I have a 2000 4Runner V6 Automatic 4WD and have an extra A/F ratio sensor (Denso 234-9002) which has never been installed, (new in box). If you want it, I can sell it to you cheap. See the following link for the sensor I have. See if it fits your vehicle:

http://www.amazon.com/gp/product/B000C5YCYS/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1

Here's a link for cross referencing DENSO part numbers with Toyota:

http://www.densoproducts.com/Den-Aut-l1351.aspx