another idle issue...

whincup · 11-08-2009, 06:53 AM

i have a '94 sierra/samurai with the stock 1.3L engine... anyway tonight i was out driving: it started fine, and was running fine. stopped at traffic lights and idled fine. five minutes later i was home, and once i stopped the idle speed was fluctuating between 200-500 rpm! the engine wasnt hot or cold, it was well within proper range. i took it back for another drive immediately, theres no power loss and it runs fine, but as soon as its stopped, its back to odd idling!...
anyone have any ideas as to what might be causing this?

Baratacus · 11-08-2009, 09:05 AM

does it only happen at night when the lights are on? It could be the alternator going bad or it could be your idle compensator. When you run devices that put a load on the engine, like the Headlights, or the ac, or power steering, the idle compensator bumps up the idle so that it doesnt stall out under load. If the idle compensator is getting a faulty signal or is dammaged it could cause erratic behavior of the enging at idle.

whincup · 11-08-2009, 04:00 PM

heater and lights were both on, but it made no difference when i turned them off... but i'l try it longer than a few seconds today...

whincup · 11-09-2009, 04:22 AM

strangely enuf, its running perfectly fine now...

Baratacus · 11-09-2009, 09:04 AM

could be a dirty ground or connection that is only going to act up on you when when it's damp with condensation. If it's your idle speed control then it only comes on when the engine is at normal operating temperature.

whincup · 11-09-2009, 04:09 PM

ahh... it was raining at the time. goin away for 3 days so cant look into it til after that...

whincup · 12-11-2009, 05:53 AM

rather than starting a new post, i figured i'd just go off this one again. its now doing the opposite by idling high... runs fine, but when stopped at traffic lights, it idles anywhere between 1200-1700rpm... however if u ram the throttle to make it jump to about 4k, it drops straight back to normal. next set of lights its idling high again, but same solution works again... anyone got any ideas as to what the problem could be?...

dont know if this has anything to do with it, but last sunday i went through mud that covered the sidesteps (it has 2" lift), although the problem didnt start til tuesday...

Baratacus · 12-11-2009, 10:58 AM

Take the hat off the carb and clean the linkages and springs. It sounds like the idle cam might be catching. It should kick down automatically but if it's gummed up or the plunger isn't functioning right it will prevent it from releasing whithout kicking the throttle open. Also check to make sure you didn't blow a vacuum line off. I do that every once in a while when I'm runing it hard. If the throttle body hiccups, it can blow a vaccum line off of its port, especially if the hoses are getting old.

whincup · 12-12-2009, 01:21 AM

just had a quick look... i think it could be the spring that pulls the throttle cable back when your foots taken off the pedal, the one thats just behind the carb... it doesnt seem to want to pull back properly, had a play with it by revving it, waiting for it to idle high, then help the spring by pulling it manually.

will any spring work for this, or do i have to get one exactly like this particular spring?

Baratacus · 12-13-2009, 04:03 PM

check to make sure that there isn't an arm or a lever loose that releases a catch on that return spring. I've not yet heard of a carb spring going bad but I guesse it could happen. I don't know what you would use other than a stock spring from a busted carb... is the spring just not strong enough? Maybe the return mechanism is too stiff rather than the spring being too weak?