89 740 rough Idle(non turbo)

nisan17 · Post by **nisan17** » 07 Feb 2012, 16:53

Hi Esteemed group,
The last couple of months my check engine light has been on. The engine still runs smooth. Until recently, when the engine is warm, and upon pulling up to a stop sign or stop light there is drop in rpm to the point of almost stalling, then it idles rough at about 500-700rpm. I've also noticed that there are exhaust soot spots in my drive where the car warms up in our cold Wisconsin Winters. Can one give me an idea what is causing this? If I can have the system scanned where Is the connector? I can't seem to find it under the dash on the driver's side.

Thanks much in advance,

Post by **billofdurham** » 08 Feb 2012, 11:43

Kevin,

The On-Board Diagnostic unit is in the engine compartment. You do not need a scanner. The instructions for its use are pinned at the top of the forum.

Usually on these engines when the idle is jumping around the throttle body needs cleaning. However, as you have a check engine light, read the codes first.

Bill.

nisan17 · Post by **nisan17** » 09 Feb 2012, 12:52

Thanks Bill.

nisan17 · Post by **nisan17** » 09 Feb 2012, 21:51

Bill, If I checked the OBD correct, the code gave "Throttle Switch" Now what? I'm going to clean the throttel body and reset the OBD.

Post by **billofdurham** » 10 Feb 2012, 12:47

Kevin,

If the code was 1-3-3 or 2-1-3 you can only check the throttle switch itself. The attached tells you how:

740 throttle switch check.pdf: (112.71 KiB) Downloaded 258 times

Cleaning the throttle body will do no harm.

Bill.

nisan17 · Post by **nisan17** » 27 Feb 2012, 18:20

Bill, how is the throttle switch replaced? It's running pretty rough, actually more so after cleaning the throttle body.

Thanks,

Post by **billofdurham** » 28 Feb 2012, 12:05

Before spending money on a new switch you can run two checks on the switch itself to see if it is working.

1.

740 throttle switch check.pdf: (112.71 KiB) Downloaded 185 times

If it is working try adjusting the switch.

2.

740 throttle switch adjustment..pdf: (65.83 KiB) Downloaded 169 times

To replace the switch remove the two retaining screws and the electrical connector. Replacing is, as they say, reverse of the above but the switch will need to be adjusted.

Bill.

nisan17 · Post by **nisan17** » 28 Feb 2012, 21:48

Thanks Bill. As soon as we dig out I'll test same.

Thanks again,

nisan17 · Post by **nisan17** » 17 Mar 2012, 15:29

Bill, is the throttle switch the same as a "TPS"? One supplier calls it a "Throttle Position Sensor" TPS. I just want to make sure.
Thanks again,

Kevin

Post by **billofdurham** » 18 Mar 2012, 12:20

Some call it a throttle position switch, others a throttle position sensor. Either way it is abbreviated to TPS. They are one and the same.

Bill.