c4 cross fire
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Welcome!
We need to know what "Getting to idle down means" How high are you idling?
You have a couple of things to consider
1) vacuum leaks. This the most likely culprit of a high idle. Start here- I bet you find lots.
2) Dirty/non functioning IAC valves
3) Adjustment of the TPS
Also, if you don't have a Field Service Manual (FSM) buy the book (not the CD) as soon as practival. It will really help you out a lot.
We need to know what "Getting to idle down means" How high are you idling?
You have a couple of things to consider
1) vacuum leaks. This the most likely culprit of a high idle. Start here- I bet you find lots.
2) Dirty/non functioning IAC valves
3) Adjustment of the TPS
Also, if you don't have a Field Service Manual (FSM) buy the book (not the CD) as soon as practival. It will really help you out a lot.
Burning Brakes
Joined: Apr 2016
Posts: 781
Likes: 73
In the case of my '84 the high idle was caused by a failed front coolant sensor. The ECM uses the front coolant sensor to determine how fast to idle the car while it warms up. If it never "sees" the car warming up it will idle high forever.
Dirty/failed IAC valves tend to cause more of a rough idle than a high idle. Not difficult to take apart and clean....just need a big enough socket.
Biggest cause of vacuum leaks on the cross-fire is the top plate of the intake.
Also don't rule out a failing MAP sensor.
Dirty/failed IAC valves tend to cause more of a rough idle than a high idle. Not difficult to take apart and clean....just need a big enough socket.
Biggest cause of vacuum leaks on the cross-fire is the top plate of the intake.
Also don't rule out a failing MAP sensor.
Racer
Joined: Feb 2014
Posts: 275
Likes: 14
From: Gahanna, Ohio
I cut my teeth with the C4 on a 84 also. I also had the same problem. The good news is the problem is easily solved, you just have to understand the operation of the crossfire. 1st thing is to replace the temp sensor that was previously mentioned. It's cheap and easy to do, it tells the computer when to close the IAC's due to engine temp.
Second is to locate both IAC's and remove them, clean them good, replace and visually look for any vacuum leaks, lines off etc. After you do that if you still have high idle (this engine can take a minute or two to lower the idle) there is a screw on the linkage to control the idle and you can turn this to lower the idle.
My vette was abused by someone who didn't understand this system and raised the idle to mask other issues. You will eventually want to make a tool to balance the TBI's. There is a lot on the web on how to do this.
Second is to locate both IAC's and remove them, clean them good, replace and visually look for any vacuum leaks, lines off etc. After you do that if you still have high idle (this engine can take a minute or two to lower the idle) there is a screw on the linkage to control the idle and you can turn this to lower the idle.
My vette was abused by someone who didn't understand this system and raised the idle to mask other issues. You will eventually want to make a tool to balance the TBI's. There is a lot on the web on how to do this.
