I hope this is the right category. I do have a 305 tpi but my problem seems to be the idle control valve? My car does great on the open road but there does seem to be a little loss in power mainly at low speeds such as 20 or 35 mph here on base. The RPMs will go crazy at a red light or stop sign. If I run the AC and stop at a red light, it will die usually within 5 or 10 seconds. It's not too bad right now because it's hot and I can just roll the windows down here in North Carolina, but when it gets cold it's going to suck if I can't run the heat. It's a very clean car and is in otherwise great condition. It sure doesn't look like a 20 year old car. I just got back from a deployment and now it's doing this. My wife did drive it and it did have a tune up, oil change, and fuel, oil, and air filter change. She took care of it and drove it. But I'm guessing it's the idle air control valve? A buddy of mine (who is into muscle cars and much more mechanically inclined than I am) told me to adjust the screw on the IAC to bring the RPMs up but should I torque the screw in pushing the lever out? Or torque it out, letting the lever in some more? Because I also heard that carbon may build up on the valve and it will not shut all the way so the RPMs will be funny at idle just like mine. Also, will the AC really effect it and cause the engine to die if it is the IAC? Any help is much appreciated because I am no mechanic. Thanks and God bless.

 

Sorry, I forgot to mention that the RPMs will set at around 700 at a red light or parked and will wiggle a little bit and drop down to 500 or even lower and then shoot back up to around 900 or 1000 RPMs and settle back on 700. Some times it will just settle at 500 and stay there.

 

First of ALL, you need a TPI manual of some sort and you need to study it! You need a lot of information as to how this system works BEFORE you start turning screws. One of my first TPI books was the SA Design book SA54 "CHEVY TPI Fuel Injection Swappers Guide". This book is old, but it covers the basic TPI pretty well and will help you understand what is going on in yout TPI equipped car. Do some reading FIRST, before you screw up some really expensive components due to being uneducated about TPI.

No offense, but your "buddy" may not be your best source of information. You cannot "Adjust" the IAC, the ECM controls the IAC, this IS NOT adjustable! The IAC is a small electric "stepper motor" that moves a plunger in and out to control the idle speed. DO NOT try to "adjust" the motor! Is the screw you are talking about "torquing in" on the driver side by the throttle cable? If it is, that is the base idle screw, do not mess with that until you do some reading and know what you are doing.

What you can do is set your base idle speed and check the TPS (throttle position sensor) voltage. You need to make sure that the IAC motor and the IAC ports on the throttle body are clean and free of carbon deposits. Make sure the throttle plates are clean. Sounds like a sticky IAC or a bad TPS. The IAC is opened and closed by the ECM to control the idle speed to match a number that is programmed into the EPROM. So if the car ECM is programmed to idle at 600 RPM, then the ECM commands the IAC to open or close, based on load, to maintain 600 rpm. So, yes, when the a/c kicks in the IAC opens a little and maintains 600rpm. when the a/c goes off the load decreases and the IAC closes and maintains that 600RPM. Same as when you put the car from park to drive, exact same scenario. ANY increase or decrease in load to the engine will initiate the same sequence of events. The ECM is going to keep the idle speed at the speed programmed into the EPROM. Every component in this system affects what another one does, there are no "unnecessary" components! So if the TPS is bad the idle may not be right. If the IAC is bad or sticky, the idle may be very erratic! Get a TPI book, read it and get back to us BEFORE you get your tools out.

 

Thanks! That is a lot of helpful info and I will definitely get a TPI manual as I plan to keep this car for a long time. And no offense taken (about my buddy). He seems like he knows his stuff but there is a mentality around here and people don't really think before they do something, or in this case tell someone to do something. Like I said, I'm no mechanic and yes I meant the base idle screw by the cable. I did read somewhere on here about synchronizing the IAC and TPS. I also read that is should be cleaned. But I've also read that you can just adjust that screw to fix it and I've also read that you should not clean the IAC valve. So it's just good to read some supporting info to SOMETHING. I will definitely get a manual like you said. And I will read it. Thanks a lot

 

The IAC can be cleaned CAREFULLY. Just be really careful. Do not submerge it in strong solvents, etc. Hand clean, do not use abrasives, do not get it wet, etc.