About a year ago, I installed an in-cab vacuum gauge. I saw that the reading was low, but steady, at around 14 Hg at idle. I did a lean drop on the carb, and it was perfect - steady at 18 at idle. It was that was for the whole year.
Then recently, I brought it to get new tires and an alignment at a pretty reputable place. When I picked it up afterwards, however, I noticed the vacuum reading was low again when I started it (~14 Hg) and the idle was a little rough. It has been like this for a few weeks now, but with absolutely no rhyme or reason. When the engine is cold, half the time it might idle fine and at 18 or 19 Hg, and half the time it may idle rougher and at anywhere from 10-14 Hg. Same thing when it's warm - I'll come to a stop light after driving 20 miles, it half the time it might idle perfectly at 18Hg, and sometimes it may idle a little rougher at 14.
I thought it may be in need of another lean drop, which I tried to do to the best of my ability. However, I noticed that when adjusting the idle mixture screw, I found a perfect point where the idle was as fast as it would get, but if I turned it in either direction, the idle dropped. I though that if you continue to turn out the screw once the max is reached, it should stay maxed out, and not drop.
Anyway, that didn't fix the rough idle/low vacuum problem at all. Actually today, on the way to work, for the first time ever, the truck just died on me while driving to work. While the engine was still relatively cool, I let off the gas for a second, and was just idling down the road for a sec, and it just turned off - no rough idle or sputtering - just turned off. :-( It started right back up, but scared the crap out of me since it had never done anything like that before.
So, here are my questions: Could a mechanic/kid not familiar with old manual truck tranny's have leaned on the clutch too much or something, and thrown the idle out of whack? Also, when doing the lean drop, could I have made it too lean or too rich causing it to die this morning? And most importantly, anyone have any clue what could be causing the unpredictable rough idle/low vacuum problems?
Then recently, I brought it to get new tires and an alignment at a pretty reputable place. When I picked it up afterwards, however, I noticed the vacuum reading was low again when I started it (~14 Hg) and the idle was a little rough. It has been like this for a few weeks now, but with absolutely no rhyme or reason. When the engine is cold, half the time it might idle fine and at 18 or 19 Hg, and half the time it may idle rougher and at anywhere from 10-14 Hg. Same thing when it's warm - I'll come to a stop light after driving 20 miles, it half the time it might idle perfectly at 18Hg, and sometimes it may idle a little rougher at 14.
I thought it may be in need of another lean drop, which I tried to do to the best of my ability. However, I noticed that when adjusting the idle mixture screw, I found a perfect point where the idle was as fast as it would get, but if I turned it in either direction, the idle dropped. I though that if you continue to turn out the screw once the max is reached, it should stay maxed out, and not drop.
Anyway, that didn't fix the rough idle/low vacuum problem at all. Actually today, on the way to work, for the first time ever, the truck just died on me while driving to work. While the engine was still relatively cool, I let off the gas for a second, and was just idling down the road for a sec, and it just turned off - no rough idle or sputtering - just turned off. :-( It started right back up, but scared the crap out of me since it had never done anything like that before.
So, here are my questions: Could a mechanic/kid not familiar with old manual truck tranny's have leaned on the clutch too much or something, and thrown the idle out of whack? Also, when doing the lean drop, could I have made it too lean or too rich causing it to die this morning? And most importantly, anyone have any clue what could be causing the unpredictable rough idle/low vacuum problems?
