Anyone have any idea what I need to check now?

Specs:
1990 F150 5.0 w/ 5 speed with a Cobra air intake

I cleaned out the throttle body added a new gasket, replaced the IAC, put on a new accelerator cable.

After I cleaned the throttle body and added the new IAC, the truck was idling high; therefore, I replaced the broken accel cable.

Now, the truck seems to be idling higher yet.

Curb idle is about 1200 rpm when I push in the clutch to shift the engine stays at around 2000+ rpm for about 20 seconds then drops back down to 1200-1500rpm.

I've inpected the hoses and don't see/hear any leaks. The idle isn't jumping around, it' stays at 1200rpm when stopped.

I also had the battery neg cable disconnected while doing the services mentioned above. I also just tried cleaning out the KAM.

Any idea what I should check next?

Thanks
-Ed

 

You need a starting point.
Disconnect the IAC connector with the engine running.
Does the idle change? No, IAC is stuck open, air leak at some point. Yes, IAC can be considered ok and some other fault is causing it to be open more than is should be or the throttle is being held open. Could be the new cable binding.
Recheck your work for gasket problems.

 

Make certain the throttle plate is fully closed at idle. Sounds like your throttle plate may not be fully closed due a mis-adjusted trhrottle cable or one that is too short as blugrass suggested. Also do his IAC disconnect check.

Steve

 

I pulled off the IAC connector and the engine dropped to about 850-900rpm, which seems about right. I also rev'ed the engine up a bit and the throttle was much more responsive and dropped like it used to. Definitely pointing to a vac leak. I did spray some TB cleaner around the gaskets but didn't notice a change. Considering once I cleaned out the TB this started happening. There must be a gasket leak somewhere on there. I'll test and torque the thing a bit and see if anything changes.

The other thing I noticed after putting the TB back on was my air pump doesn't appear to be exhausting anymore. Could this be a problem?

Thanks
-ed

 

Don't you know how to check your thottle plate ? Did you set it right?

Don't ignore people , I think that may have something to do with the prob as well..

 

A point I think your missing is the idle speed.
850-900 rpm is to high in any event, on a fully warmed engine.
My engine idles at about 650 to 675 with perfect starts and smooth idle.
To high an idle causes excessive creep at stops, heats trans fluid more than it needs to be etc..
The IAC is supposed to regulate the idle to a point that matches the PCM program within +/- about 50 rpm depending on other sensor input conditions.
With the IAC plug removed, it needs to be well below the normal idle speed in order to have full control of the idle under varying loads and conditions.
Not dropping to that level is an indication of an air leak that does the same thing as opening the throttle by intension.
4 cycle engines are efficiency controlled machines by the amount of air allowed to be pumped thu. The fuel supplied, only causes the air to expand into usefull power by pushing against the pistons.

 

WTH!
I'm not ignoring people. I mentioned what I did the IAC test and it checked out ok. I was also going to check the gaskets. Though I neglected to mention adjusting the throttle plate. And no I don't know how to adjust the throttle plate. I didn't even notice an idle adjustment screw when I pulled the TB off.

My apologize to you Steve, which by the way, I did take your advice and replace the "Your quote - fricken IAC".

 

There is a stop there but is designed to be difficult to adjust.
Do not make any change in opening unless someone else has changed it to an improper setting making it nessasary but then you need to know what to do and the reasons behind the setting.
To far closed and the plate can stick in the throttle bore when the engine cools.
Not good.
To far open and the idle gets to high, the IAC cannot properly control cold starts, various idle loads etc.

 

Thats not what was ment - If you unscrewed the throttle plate inside the throttle body to clean, you have re-install the plate properly by leaving the screws loose and snaping the plate shut a times - then hold and tighten screws.

What can happen is the plate can be letting to much air by @ idle. This causes a high idle

So WTH - has this been done then?

 

Thanks for the RPM values. I'm definitely off here. I read on another post people talking about the 302 is known for an intake manifold gasket leak near the firewall.

As far as the throttle adjustment, I have no idea if someone has changed it in the past. I brought the truck into a local shop to have the injectors flushed out, I don't think they touched the TB. I'm not sure if it would be a good thing for me to go in there and monkey with it either. Like Steve pointed out it sounds like I could have a throttle plate adjustment issue in addition to a vacuum leak.

Before cleaning the TB and replacing the IAC the truck was idling rough and would cycle high-low during a cold start. Now it doesn't do that anymore, just high idling.

I just started the engine and noticed something that certainly sounds like a leak somewhere. I didn't notice it the other day. I also don't recall hearing a weird noise after I shut the truck off. Sounds like it's coming from my fuel component block (all those vacuum lines coming into various things).

 

I never took the throttle plate off. I removed the entire throttle body assembly from the intake. I then sprayed the heck out of it and wiped it clean. I worked the throttle plate back and forth multiple times to ensure it wasn't sticking. No screws were touched during this operation.

Here's preciously what I did when the neg cable was disconnected
1. Removed TB from intake
2. Cleaned TB and intake ports
3. Installed TB back on
4. Started engine - idle was too high when warm and cyclic during cold start
3. Replaced IAC
4. Started engine - cyclic behavior was gone but high idle remains
5. Noticed accelerator cable was broke at the plastic end, replaced it with one of the same size
6. Stated engine, problem remains

 

Sounds like you are onto something now - if you hear what may be a vacuum leak, that can certainly cause a high idle. Now you just have to try to nail down what's leaking and fix it.

 

Never take the plate off the shaft for cleaning because you can't get it back on in the same location without backing off the stop to regain centering; then you back into the throttle stop deal again.
You upset the stakeing of the screws. It's not worth the hassle.

 

Unless you port & polisher her . I put a light inside body and trigger the mechanism a few times and then check to see if there's any light coming thru the seams - works to find exact center of the two when they come together.

I agree w/Bluegrass on the stock unit.

Reading to many posts I guess , I thought you may have had her all apart - my bad.

Good Luck.

 

Seems like everytime I get in there, I find another STAR (sh*t that ain't right).

I'm suspecting my intake gasket has gone bad. I sprayed around all the hoses as well as the TB. No change in idle or suction evident. I can hear this thing or I think that's what I'm hearing.

The other thing I noticed is while the truck is running I hear a loud buzzing coming from my gas tank. I also hear something some kind of motor running after I shut the truck off. Sounds like a fuel pump. I would think that if my fuel pump is crapping out that it would add some more variety to my idle issue.

Ideas?

-Ed