tmpusfugit

I have investigated "search" and have read a great deal about these sorts of issues but most of it seems to be on later cars...mine is an '84. WSM has not been helpful either......

Ok, original problem on '84 auto USA version, car had sat for a long time. Gas was drained, a lot of work has been done including new hoses for gas, vacuum, water etc. Upon completion of work the car started up readily but had cold idle of about 1100 rpm. Modest amount of investigation shows idle switch not actuated at closed throttle. Adjusted idle switch so that it actuates at closed throttle.

After the adjustment to the switch: Cold start car now oscillates between 400 rpm and 1100 rpm every 5 -10 seconds while cold/cool. After about 3-5 minutes of the oscillations they become less frequent and less variation, and finally go away. (car will behave normally off the closed throttle position starting at about 1100 rpm).

The engine, now a bit warm, seems to settle in at about 900 rpm in park or about 650 rpm in gear, which I understand to be in the "normal range". The car has a new 3 wire O2 sensor, no apparent vac leaks so far.....I am guessing I have a bad temp sensor but any suggestions as to which one, or am I barking up the wrong tree? Any recommendations as to the next logical steps to take?

tmpusfugit

bump, any suggestions?

Hkp7

My 84 did the same thing, check for power and ground at the plug for the auxillary air valve. If both are present, remove the valve and see if it closes with 12 volts applied. Heating the valve will also cause it to close. On mine, I had power to the plug, but the ground was no good. Hope this helps.

tmpusfugit

Thanks, I will give that a try tomorrow....

z driver 88t

My 84 used to have an idle oscillation problem, although not as significant as you are descibing. Turns out my O2 sensor was bad. Very easy to diagnose - you can unplug the O2 sensor at the fuse panel (heavy gauge wire near the bottom of the plywood piece). My car immediately smoothed out when I unplugged it. I adjusted the idle mixture using a long 3mm allen wrench and a wideband O2 meter (it turned out to be rich), then got a new O2 sensor.

tmpusfugit

Auxillary air valve tests OK. There was a nasty kink in the hose now corrected, no real improvement, I disconnected the O2 sensor, and of course the connector fell apart in my hands. With the O2 sensor disconnected I was able to lower the idle down to a smooth (no oscillations) 750rpm, but I have no real idea where the AF mixture might be right now, so I have work to do in finding the "correct" O2 sensor as well as a wideband A/F meter.

In a related question does anybody have any idea why the "funny" connector on the O2 sensor? I can't think of any logical reason for the unusual design...and do the usual purvayors of 928 stuff stock just the connector? I know, ask Roger, and I will....

Thanks to z driver 88t and Hkp7 for the suggestions, they both helped!

karl ruiter

I would guess an air leak. Possibly injector seals. Also there is a seal between the plenum and throttle body that can crack.