Throttle Position Sensor/Throttle Switch Adjustment

[westsidex]

I have a 91 Metro with a manual trans. I'm at a loss here. The engine idles erratically. I checked all hoses for leaks/cracks and found none. I adjusted idle speed and TPS/TS (which was so far out of wack that it wasn't even generating a reading on my multimeter), and checked ISC valve and still cannot get a steady idle. At 800 RPM, the engine vibrates too much for me to call it steady, because I run my headlamps all the time for visibility purposes (a poor man's DRLs if you will) and with them on the idle RPM drops to around 500. If the engine cooling fan comes on, it almost kills the engine. I bumped the idle speed up to 1000 RPM to compensate for the headlamps being constantly on, which has helped, but the engine still likes to lope and surge about 100 RPM, which causes a momentary vibration of the engine which I find annoying. Believe it or not when I run the A/C, the idle speed will sit constant at about 1200 RPM, no surges or lopes and, though it doesn't shake, it is still loud. Is there anything I have missed? Also, Chilton's outline for adjustment is difficult for me because I don't have a feeler guage on hand, and it makes references to "throttle stop screw" and "throttle lever" which I cannot seem to locate/identify. How, in your opinion, should I go about adjusting the TPS/TS? Finally, I know the engine should be set to 850 RPM, give or take 50 with no accessories running, but where should it idle with the A/C on?

[geozukigti]

The A/C has it's own idle air valve. It's the little black can with a big white knob on the firewall next to the wiper motor. You can adjust the A/C idle with that white knob. I would re-set your ignition timing, and do a full tune up. Sounds like your engine isn't generating enough torque at idle to run the alternator. If the engine is shaking, it could possibly be pre-detonating.

[westsidex]

Full tune up done recently by me, but I never timed it. I know about the A/C idle speed valve. I personally set the A/C idle speed. However, I find it odd how it doesn't surge and lope with the A/C on. Anyway, what is your recommended idle speed with the A/C running?

[geozukigti]

I would keep it around 1000rpm's, to keep the coolant flowing decently.