hey guys. . . 89 f-150 302 manual.
The air pump has been removed. EGR doesn'twork because holes in rear of heads for the exhaust to run back through is closed off. Idles around 2000 and after a while might drop down to about 1450. With the IAC valve off it idles around 1200 I think. What is the PVC valve? where is it located. I can't seem to find vacuum leaks. . . whats a real good way to check for them? I remember my idle used to fluctuate between 500 and 1500. Every time I would pull out of gear coming up to a stop. . . truck would die. I would kick the clutch in third and it would run like normal with the fluctuation. I replaced the upper and lower intake manifolds from another truck and now it just idles high. What do you guys think? Help. . . I want normal idle.
Timothy

 

I usually spray carb cleaner at everything while the truck is running. If I hit a leak the idle will change for a short time. The PCV should be sticking through your valve cover with a rubber hose going to it. Take it out and shake it. If it makes noise it is probably working. It is a cheap part if you are in doubt.

 

Might possibly try a full tune-up. PCV = Positive Crankcase Ventilation. I drive a 93 f-150 and after visiting my local salvage yard a few times, I have found that as far as engine component placement- our trucks vary only slightly. My PCV valve is located right behind my passenger side valve cover. It is almost hard to spot unless you know what you are looking for. Trike is right in saying there will be a rubber hose attached to it. In my case the hose is L-shaped. Costs around $2.19. Good luck!

 

Sounds like one of the intake gaskets is leaking. The lower intakes have a tendency to leak, especially at the back. When the rpms get to about 2k, it's usually a big vacuum leak.

The intake gaskets seem to pretty sensitive. Did you use a torque wrench and the patterns from the manual to tighten down the intake manifolds? They really don't need a ton of tightening. about 22-25 ftlbs. I did mine in three steps, like heads, just to make sure it was good. They uppers are only 12- 18 ft lbs which is very light, to me.

 

the engine is a fresh rebuild. . . so no tuneup shouldn't be necessary. I know where the pcv hose is. . . its not on there anymore, I think I lost it. But where is the valve? is there a valve inside? what happens if its not connected? the two front bolts on my upper intake manifold broke off. . . I thought maybe that was the vacuum leak. . . kinda hope maybe it is. . .because then I have located the problem. I tried the propane trick. . . let a propane torche unlit leak gas while it was running. . . didn't do anything. I'll try carb cleaner. as for egr. . . do I need the airpump to make that work? need a new fan belt soon anyway. Thanks guys. . . check back in a few hours
Timothy

 

ok so now Iam back to where I was before I replaced my intake manifolds. Turns out the vacuum leak was the connection between the passenger valve cover and the upper intake manifold wasleft open. Thats about a 3/8's inch hole. . . but now it goes between 500 and 1500 rpm. Disconnect the iac and it dies. I am 99% sure its not the tps or it iac because i have had multiples in there. . . and they all did the same thing. So. . . what causes this? Thanks.
Timothy

 

The intakes gaskets on the 302 are a little prone to leaking anyway. I would be concerned about 1 broken bolt, 2 is bound to cause a problem. It might not be your vacuum leak, but it will probably end up a water leak. If anti-freeze gets in the oil it will eat through the bearings pretty fast (and the intake manifold is where it usually happens on these engines.)

It's very possible that it is your vacuum leak. It could be sucking air from the bottom, instead of the top.(?) The easiest way to tell for sure is probably just to fix the two bolts, and re-torque the intake manifold.

-

Idle surging, most likely causes: vacuum leak, bad map sensor, bad iac, bad tps. It sounds like you replaced the iac and tps already. you could try unplugging the map sensor, and see if it steadies up (the mixture will be off). There is a procedure to test it, but it takes a pretty fancy meter.

 

its the upper manifold that is missing two bolts. . . so no antifreeze flows there. . . however explain this sucking from the PCV more. . . because I feel a little suction from it. . . very little, but I don't think there is a vacuum leak at the manifold,
Timothy

 

ah, that sucks... (hahaha sorry)

ok seriously

Well, the pcv is supposed to let the intake manifold suck air out of the valve cover. If the intake manifold (lower) gasket was letting air in from the vally, then it might suck air backwards through the the PCV hole in the valve cover. Normally it shouldn't have a vacuum there, the vacuum comes from the hose.

Just an idea to try to explain where the extra air for the vacuum leak is coming from.

That's good that it's the upper. It could still be leaking. The uppers only get 12 -18 ftlbs of torque. Did you go around the upper gasket with the torch? what about the TB, did you change the egr gasket? just trying to cover all the bases.

 

I see. . . however between the two manifolds(upper and lower) there is no connection to the crank case. . . so that wouldn't creat a vacuum. . . unless there is a leak between the intake and the crankcase correct? Make sense?
Timothy

 

exactly.

They seem to leak pretty oftern. Nothing personal. I made sure to follow the torque readings and pattern for the lower intake manifold. I babied mine and did it in 3 steps to make sure I didn't have to do it twice.

 

good plan, I'll check that out to make sure. . . you know the torque setting? Will this affect my idle at all you think?
Timothy

 

The uppers and everything that bolts into aluminum is 12-18.
The lowers are 22-25 ftlbs, with a torque pattern of
pass front . . . . . . rear
5 1 9 11 3 7
6 4 12 10 2 8
driver side

The book says to tighten in steps. So I went to 12, 18, 22, 22.
You always end up a hair tighter than the wrench says when you double check, so I figured I'd wind up at 25.

If it was leaking it will.

Be carefull with those rigid (crispy?) vacuum tubes if you have them. The break like they are made of glass. I had to replace a couple.