Rough Idle after Vacuum line replacement (1 Viewer)

[Aggiesdm]

Hi all, As part of the PM for my rig, I decided to replace all the vacuum lines and see if it helped with my slow acceleration under 2000 rpms. I replaced all the lines and it seems to be responding better to the accelerator, but now it has developed a rough idle. Seems to jump around in the low 600's. This wasn't there before I changed vacuum lines and I didn't do anything else mechanically. I've read a few post that said the vacuum modulator could be the culprit, but not sure. Since mine is a '91 3FE, I don't know if it would throw a code or a CEL . Either way, it isn't showing any CEL and seems to be running fine once I'm driving...only the idle is rough. I've checked my EGR and seems to be functioning fine.

Also, seems to take a bit longer to start.


Any thoughts? I've had a hard time following some of the other post because they all seem to be for 1FZ's, not 3FE.

 

[Aggiesdm]

BTW, I've already checked the main intake hose off of the air filter and it is fine.

 

[jonheld]

You have a vac line swapped.

 

[Aggiesdm]

I'll check, but I did each one individually, so little room for error. The only question I have, is what direction should the little check valve near the vsv's be flowing? I might have got it backwards?

 

[jonheld]

Flip it round and see what happens. You can't hurt anything by playing around with vac lines while the motor is running.

I still would be willing to bet you reversed a line somewhere. Try swapping the 2 small lines that run to the feed through on the intake tube. Swap just the passenger side.

 

[Aggiesdm]

So I swapped the lines as suggested...no change. I also flip/flopped the check valve ... No change. Still idling rough. Not horrible, just enough to irritate.

 

[jonheld]

Then you're going to have to go through each line 1 by 1 and pull it and look for a change. Something happened when you replace the lines.

 

[sailfish014]

Is there a manual which says which line goes where? I got my LC80 with 3FE engine which was converted from right hand drive to left hand... and I'm not pretty sure if the lines are fit properly/correctly...

 

[Aggiesdm]

Is there a manual which says which line goes where? I got my LC80 with 3FE engine which was converted from right hand drive to left hand... and I'm not pretty sure if the lines are fit properly/correctly...

There should be a diagram sticker under the hood on the US driver side.

 

[Nonprophet]

It's possible that while you were changing the vacuum lines some crud came loose from one of the rubber lines that dropped down into the metal lines. I'd get a piece of wire and clean/ream out the metal lines--can't hurt and they often need cleaning anyway.

 

[M32H32is]

I believe the 3fe has an idle adjustment screw. You may want to adjust the idle?

 

[Aggiesdm]

Tanks for the suggestions. I'll try cleaning the lines a bit.

 

[Aggiesdm]

So, I've checked the vacuum lines against the diagram and all are correct. I'm curious about where and how much vacuum I should feel at any given hose. There are only a couple where I can feel/hear any vacuum. Are some open and some closed at different points/rpms? Also, the hoses fit very loosely on a few of the hard lines. Seems like they should fit more snug. Thoughts? On the PS of the truck, I feel/hear no vacuum out of the lines at idle.

Ps. I did "test" the EGR valve by sucking on the actuator line until the motor almost died, so seems to be working.

I'm so unfamiliar with vacuum stuff, I'm a little frustrated.

 

[Aggiesdm]

Well, I have a idea what the problem is. I went to the dealer to get the vacuum line and he told memo get it from Autozone because it was the same and much cheaper. Looks like he was wrong. I've compared the aftermarket hose with an OEM one and there is a very slight difference in the interior diameter. Aftermarket is slightly larger and I think I'm getting seepage around the connections. Will get OEM and check it again. Fudge

 

[sailfish014]

Thanks Aggiesdm... But mine doesn't come with it...

 

[Timpanogos Slim]

Well, I have a idea what the problem is. I went to the dealer to get the vacuum line and he told memo get it from Autozone because it was the same and much cheaper. Looks like he was wrong. I've compared the aftermarket hose with an OEM one and there is a very slight difference in the interior diameter. Aftermarket is slightly larger and I think I'm getting seepage around the connections. Will get OEM and check it again. Fudge

It's more a question of getting the right size.

I used 3.5mm ID silicone line i bought from "nxs motorsports" on ebay and it has been working great.

Now i just have to test my idle air control solenoid. I went from intermittent rough low idle to intermittent smooth low idle. 300rpm and rock steady.

Edit: I have a 1FZ-FE engine, so, dunno if the vac lines are the same size on your 3FE.

 

[jonheld]

I believe the 3fe has an idle adjustment screw. You may want to adjust the idle?

I've said this before in other threads and it doesn't seem to sink in.

THERE IS NO IDLE ADJUSTMENT SCREW ON A 3FE.

The idle speed is regulated by the ECU in conjunction with the ISC valve and TPS along with other sensors. The "golden screw" you're adjusting is setting the static air flow with the ISC valve closed. The more you adjust the screw, the more the ECU will attempt to compensate.
While adjusting this screw will have an effect on the idle speed, it is only temporary until the ECU makes adjustments.

Idle is supposed to be 650 rpm.

 

[Aggiesdm]

Thanks Aggiesdm... But mine doesn't come with it...

I can take a pic of it if you'd like me to and post it. Let me know.

 

[scrowley]

Maybe you had a vac leak before that the ECU compinsated for and now you fixed a leak and the ECU needs time to catch up. Just a guess. Also any time work is done/completed your immagination will make things up and you will hear, see and feel things that where always there. I do that all the time. Drive myself crazy over nothing. I would put some high test gas, fuel system cleaner and drive it and see if it returns to normal before chasing your tail for nothing.

 

[sailfish014]

I can take a pic of it if you'd like me to and post it. Let me know.

That will be really helpful, Aggiesdm... Kindly do. Thank you very much!