Ogriv

Greetings,

I have a problem with the idle of my impala. At this point it appears to be random but annoying issue. Sometimes it occurs when the car is started, other times it occurs after the car is warmed up. My car does not have a tach so I can't say for sure how fast it is running, but by the sound of it, I think it's running an Indy race!
The Service Engine Light does NOT come on, although it did when I unplugged the Throttle Position Sensor, but the light went back out when I disconnected the battery). I have had this occur with or without the AC being on. This fast idle aslo causes the temperature to rise above half. The temperature is normally a few clicks below half.

Things I have tried:

1) Cleaned the IAC valve and also checked the Ohms between pins A & B also C & D and both measured 51.6 ohms.

2) Replaced EGR valve and Gasket with new GM parts. (The car ran good for a week after changing this)

3) Cleaned the MAF sensor (The little filaments in the Cold Air Intake Tube)

4) Cleaned the Intake and butterfly with carb cleaner

5) Replaced a small U shaped vacuum hose connecting the PCV valve to a sensor of some type. (It is located just in front of the EGR valve and was actually collapsing when the car was started. This did not actually seem to affect the idle with or without the tube installed.)

6) Verified that the Cruise Control cable was not engaged.

7) Verified that the Throttle cable was not sticking.

Can I read the codes myself or do I have to take it to the shop?

This is my wife's everyday car so I need to get it fixed!
I would appreciate any assistance with troubleshooting this issue.

wanderson75

Two things off the top of my head come to mind.

1) Disconnect the throttle cable to the Cruise Control. I actually had mine stick on me not too long ago. And it doesn't need to be stuck far to get a 3400 to rev up.

2) Check your vaccuum line from the brake booster to the intake manifold and also check your breather from the intake pipe (next to the IAT Sensor) and make sure the other side is hooked up in the back valve cover.

You can also try running it with the MAF sensor disconnected and see if it changes anything. What did you use to clean it with?

__________________

Ogriv

I disconnected both cables going to the throttle just to check them out. The cruise control actually has a little slack in it, so I don't believe that is the problem. I cleaned the MAF sensor by spraying it with carb cleaner.
Tonight, I disassembled the intake and cleaned out the tunnel from the EGR valve to the the intake I cleaned both sides of the intake assembly. It is now spotless. I also scrubbed out the tunnel for the IAC valve. It is also now spotless. The only real carbon build up that I saw was right where the exhaust gas enters the intake. I also replaced the thermostat, just because I had everything already out of the way and I just considered it preventative maintenance. I started the car and refilled the antifreeze, worked out the air bubbles and let the car come up to temperature. I started and stopped the car 7 times and could not get the high idle to return. I will start the car first thing in the morning to see if it returns.
When I examined the IAC valve, the ohms were correct but the actuator seemed very stiff, should I be able to easily move it in and out with my hand? Perhaps it has a mechanical issue that is randomly causing me this problem.

I also rechecked the breather tube and the vacuum line to the booster. They appear to be OK. I also used carb cleaner and sprayed all around the engine and the vacuum lines to find a leak, but the engine never sped up at all.

Ogriv

I just noticed a weird symptom. When I am manually moving the throttle plate and I make the engine accelerate while in Park, the engine will "miss" when I really give it the gas. It seems to rev up just fine, but then when I really get the RPM's up there it "misses" repetitively, almost like the steady rhythm of a rap song. Does the computer realize that the car is in park and so it is acting like a governor, or do I have another problem?

Ogriv

The car is still running well! Perhaps all it needed was a good cleaning!