RylerTust

1990 4runner
22re
5speed
4wd
Ac
Ps
244k miles

I've been having weird idle issues since I got this rig, really, but since the beginning of summer it's been getting worse and worse. I fixed it for a while, now it's bak in a weird way. Idle drops from 750 to ~400 when I come to a stop. If I pop it in neutral, rol down the street, idle is normal. Come to a stop, idle drops. Almost seems like it does it the harder I hit the brakes. What could this be??

I'm checking my egr and vsv right now since I got a smog pretest and apparently my NOx is slightly over. So either vsv egr or cat right?

coryc85

Vac leak in your brake booster sounds like.

RylerTust

Thank you for the reply, Cory. My brakes feel as good as ever, with the truck off and me depressing the brake pedal, in two pumps the pedal becomes very stiff. This means the booster is good, right? How do I check for vac leaks? Would I need someone to press it while running when I spray for vac leaks?

RylerTust

Also, all vsv things check out, I have three?? And it's not even a California model? I don't know but all pass. Egr valve moves but it takes a bit of suction. I'm using my mouth as a vacuum pump and It needs a bit to move. Is this normal? It's only supposed to move under hard acceleration so there would be a lot of vacuum on it right?

lobukbuild

I had a similar issue years ago. evry time I stopped the idle would drop, eventually I discovered that it was occurring every time I pushed in the clutch. which every one does when they come to a stop. turned out to be the thrush spacer on the crank. pushing in the clutch pushes on the crank and forces it forward and causes binding on the rod bearings. not saying this is your problem but it would be worth checking.

RylerTust

Oh dang, I'll get it warmed up and go exparimet with clutch and brake combos. Worst part is its not all the time. Also it changes with a/c. When the compressor is on, idle is normal, comp shuts off, idle drops low.

4Xtruck

Have you removed the air intake hose and looked inside your throttle body? It could very well need cleaning.

RylerTust

Throttle body and all that is clean. Clean filter. Cleaned MAF/AFM. It's not the clutch as far as I can tell. Also on warm start, idle is low when first started.

RylerTust

SO! I've been workin on this thing all day. As far as I can tell all is in working order so my high Nox is from a bad cat I think. And the idle, when I am parked and pump the brakes, idle drops. What's this mean?vv

4Xtruck

Open up an unlit propane torch over your vacuum lines, including the brake booster, while your truck is idling. If there is a vacuum leak, the propane will be drawn in and the idle will increase. You may want someone pumping the brakes while you do this.

Kiroshu

Internal brake booster diaphragm vacuum leak sounds like.

RylerTust

Had my lady pump as I sprayed carb cleaner all over and no noticeable change. I'm lost.

RylerTust

Pulled the line off with check valve in place, them slowly removed the check valve, ad had lots of vacuum left in booster?

RylerTust

ALSO, for the past month or so I've been getting a click/pop noise in my front end when I come to a complete stop. Brakes feel great. No viberation or anything. Could this be related? Like a leak in the rear of the master cylinder causing a vacuum leak and somehow adjusting the brake pressure or something causing that sound?

Ryry96

I have the same problem with my 88 pickup... did you ever figure out what the heck was going on?? Any help is appreciated!

burninggraphite

i had a similar problem for a long time and had people tell me it was a vac leak or brake booster, replaced all the vac lines and tested the brake booster which checked out fine, noticed that if i pulled the brake light fuse the problem went away.... still don't understand that one but anyway i found that my idle was set too high and if i lowered it then it was running rough, fixed it with some teflon tape ,like you use on shower heads, wrapped around the idle screw and tightened the giant nut on the egr valve and the problem went away completely.

Ron Bryant

This solved my issue - if you can wiggle that screw, you have found the issue. Goog Luck.

Ryry96

I did this a while back but it didn't help at all. Not sure what else...