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Discussion Starter · #1 · (Edited)
Hi. My name is Patrick, and I am from Pittsburgh, Pennsylvania. I own a 1998 Toyota Tacoma that I bought new. It currently has 115000 miles on it. It is well maintained, and has never given me any real problems.

A couple months ago, my check engine light came on. I let it stay on for a few weeks, and then I hooked my father's OBDII code reader to the truck. It returned an EGR circulation problem. I looked at my EGR valve, and found a loose hose. (duh!) A few weeks later I was out, and when I went out and started my truck it wouldn't stay running, it kept on stalling everytime I pressed the clutch.

The code reader is returning a PO505, which is an IAC valve malfunction. I am assuming that it is just clogged up with carbon deposits. I have a dash-mounted vacuum gauge connected directly to the intake manifold. Where my truck used to idle at about 22-25, it now idles at around 15-18. Also, vacuum pressure at all speeds and loads is about 5-10 lower than it used to be. There is no real change in gas mileage, but there has been a noticeable power loss.

In order to keep my truck running when at idle, I moved up the set screw in the arm of the throttle assembly. This makes the engine idle at about 1000 rpm, which is about 250-350 higher than it should be. But, every once in a while, the IAC valve works and the RPM jumps up tp 2000 and the vacuum goes to where it should be.

My questions are this: 1) Could the loose hose in the EGR valve have anything to do with this? I'm afraid I don't know as much as I should about emmision systems.

2) Is there any way I can clean the IAC valve, like with carb cleaner or something? If so, how do I do it? I really don't want to spend $250 right now on a new one.

My truck is a 1998 Toyota Tacoma. It has a 2.7 liter inline 4 and a five speed manual transmission. It is a four wheel drive.

Any help or advice is appreciated. Thanks.
 

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Discussion Starter · #2 · (Edited)
Well, I don't know if anyone has any answers for me, but here is an update. I removed the throttle body and the IAC valve. I cleaned the air plate in the throttle body, and I also cleaned the shutter inside the IAC valve. I checked the resistance between terminals, and also tested the valve by connecting it to my battery. All seemed to work fine.

I also cleaned the fuel injectors, and I put new AutoLite spark plug wires on. The fuel filter is also new. Same thing... low vacuum, low power, check engine light is still on. I am beginning to think that this is a computer problem.... like maybe the computer is reading the throttle wrong. Anyone have any ideas? PLEASE.
 
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