vaccuum at idle

[rb250sx]

now that i have the clutch problem figured out, its time to tackle the idling problem. I put a gauge on it today and the vaccuum was bouncing between 12-15mmHg, after starting it up for the third time, the idle was more rough and vaccuum dropped to 9-14mmHg. As for sensors, when i unplug the O2 sensor, absoutly nothing changes, and when i unplug the MAF the idle will raise and stay steady(i didnt get a chance to check the voltage on this today though). Should i be getting a response out of the motor when i unplug the o2? let me know your ideas. thanks.

[goofynick6]

Probably boost leaks, like it or not; they're always there!

[eh?]

not a boost leak since it's after the TB and at idle. here's a good website to compare your findings http://www.classictruckshop.co...m.htm

[goofynick6]

It would be a boost leak when boosting...vac leak otherwise..

[rb250sx]

well, according to that page is says "Burnt valve; combustion chamber leak." but it doesnt seem to take into account anything other than mechanical problems on that page. Im sure a sensor issue would def cause fluctuations like that. Ill have to mess around with it more next weekend, and possibly spray some throtle bodly clearner around haha. whats the answer about the o2 sensor though, shouldnt that fluctuate the rpms when i unplug it?

[eh?]

I doubt it. The only other thing that would make the vacuum drop to where you're at is opening the throttle. Your idle vac when warm should be around 18-20mmhg. You should compression test the motor.Not sure what happens when you pull the o2 sensor.

[goofynick6]

Just make a boost leak tester for $5 and test the car...it'll take no time and it shows all leaks in the engine

[rb250sx]

Well, another weekend, another failure. I buit a boost leak tester but could not build up any pressure in the system. since i moved back to NY ive been working on the car in storage and dont have power so used a bike pump. I pumped for quite a while, but nothing. When i pulled the hose off the recirc valve i could def hear air going through the little bypass hole in there though when i pumped. So i just took every single piece of IC piping and reclamped them perfect and went through all my hoses. When i started it up it idled and i got all excited, so i let it run a while. Then i decided to rev it a little bit, and when it wouldnt rev very high i realized it was idling because i forgot to plug the MAF back in so i plug it back in and it still doesnt idle. So i then checked the compression, it was 160 across all 6 cyl, anyone know if thats what its supposed to be? And then i just sat there staring at the car for a while being mad haha. Also, i noticed if i unplugged a vacuum line, nothing would change, but when i plugged it back up it would idle well for about 2 seconds. The other thing is, before i put the engine in, i did have the plenum off, and i was kind of curious about the gap on the inside of the plenum where the gasket ended. I didnt know if that was supposed to be there or not because i didnt remember it, but i didnt look very hard b4 i took it off either. But i put the gasket back in and torqued it down pretty good, and that seemed like it would keep it sealed up pretty well. I asked on the forum a while back but got no reply, so i continued with the swap haha.

[goofynick6]

You can't boostleak test w/o a compressor. And, you need the the tester pre-turbo for it all to work great. I'd guess that is probably wrong, and does it rev past 2800 rpms? If not, your maf wiring is bad.

Nick

[rb250sx]

yah i had it pre turbo, i just didnt have power for my compressor, i tried hooking it up to my inverter but it wouldnt power it. so a bike pump it was haha. Revs past 2800 fine, it was just because i forgot to plug the maf back in.

[eh?]

I reused a plenum gasket too and i think i may be having problems due to it. I have a different problem from you though, during cold starts the #6 cylinder will miss until warm. When full warm vacuum will show ~20mmhg.

Did you torque in the right sequence?