High idle problem, unable to solve. (Page 2/4)
ketstang JUL 26, 12:34 PM

quote
Originally posted by Patrick:

Covering the IAC port takes the IAC valve out of the equation... but to rule out if too much air might be getting past the TB butterfly valve (due to a messed-with idle stop screw), simply cover the entire TB opening while the engine is idling. If the engine still runs with all air being blocked from entering the TB, then there's definitely a vacuum leak somewhere. In this situation, there's no real point messing about with the IAC valve until you find where the air's getting in.




I completely covered the TB intake and the engine died immediately.
ketstang JUL 26, 12:37 PM

quote
Originally posted by buddycraigg:

If you remove the IAC and cover the hole, it should stall.
If you remove and cover the IAC hole, and the top of the TB it should definitely stall.

I bet Patrick is on the right path, and you have a vacuum leak.



I removed the IAC and covered the hole and it didn't stall.
I then covered the TB intake and it did stall.
ketstang JUL 26, 12:45 PM

quote
Originally posted by Spoon:

The most often placed missed for solving high idle on 2.8 is the cold air tube hidden behind and below the throttle body. It's a hard plastic elbow with o-ring seal that connects TB to the intake via a short section of rubber hose. My hose was mushy almost to a goooo feeling and the O-ring on the TB end was not a tight fit. At this stage it will always suck air and keep the idle high.
Another cause would be poor grounds between engine to body, engine to chassis, a weak or corroded negative battery cable, IAC connector dirty, etc.
see pic below,, Borrowed pic, Disregard the arrow. See item 5.



Spoon




I'm still messing with this issue. I decided to remove the upper intake again and I'm going to check all the vacuum hoses on the vacuum schematic on the decklid.
While I'm in there I'll check the cold air tube you mentioned and its hose/seal. I'll check your other suggestions as well.

I thank all of you in this forum for your patience with me and for your help!
ketstang JUL 26, 12:49 PM

quote
Originally posted by Jeffdylanproctor:

My car was having a very similar issue and it turned out to be the Coolant Temperature Sensor that was causing the high idle, as evidently the ECM wants the idle high till it reads a certain temp. These cars have two temp sensors, one that goes to the gauge, and one that goes to the ECM.

The one that goes to the ECM and causes the Idle issue is up right under the Thermostat housing. it is a little tricky to find and see, but it is very easy to remove. The factory plugs tend to have issues as well, and you can easily buy a plug with the sensor.

The high idle was driving me up a wall and this fixed it. Sounds crazy, but this sensor can cause a high idle.




Thanks for the tip! I will definitely be checking this next.
ketstang JUL 26, 01:00 PM

quote
Originally posted by Patrick:

You bring up a very good point, although a scanner or WinALDL would point out that issue pretty quick.

However, also keep in mind that a bad CTS would not enable an engine to idle at a high RPM with all air blocked from entering the TB (unless there was also a vacuum leak).




I did check the EGR flex tube yesterday when I took off the upper intake and it looked good.

Wish I had a scanner or WinALDL to use.

I'm going to try all the suggestions I replied to today. If it were my car I would go ahead and spring for the stainless-steel vacuum line kit, just to remove one more possibility, but it's my brothers and I'm sure he is tired of me asking for more money, LOL. He says I am "obsessed with fixing this high idle problem". I just want to get it below 2000 rpm before I return the car to him.

I'll post my finding once I FIND the problem. TY
Patrick JUL 26, 03:13 PM

quote
Originally posted by ketstang:

I did check the EGR flex tube yesterday when I took off the upper intake and it looked good.



Were you able to check the entire length of the tube? Seems to me the insulating jacket does a good job of hiding most of it.


quote
Originally posted by ketstang:

I removed the IAC and covered the hole and it didn't stall.
I then covered the TB intake and it did stall.



I don't quite understand the point of removing the IAC valve.

With the IAC valve installed, and the IAC port in the TB covered, the engine should stall.


quote
Originally posted by ketstang:

I can cover the IAC port inside the intake area of the throttle body and the car idle will drop down to 800 and sometimes it will die, sometimes not.



It's possible that the idle stop screw has been messed with and the butterfly valve is open slightly too far. Has the plug that normally covers the head of the screw been removed?

[This message has been edited by Patrick (edited 07-26-2023).]

PhatMax JUL 26, 04:01 PM
Just throwing this out there but are you sure the tach is correct ? I have an issue that the tach says it idling at 2-3k when it’s not. I did install Rodney’s tach filter but still have the same prob…..I’ll have to dive into the tach itself.
shemdogg JUL 26, 08:25 PM
Any chance the throttle cables stuck? One time messing w my intake, I had a high idle I couldnt figure out till I looked at the fuel rail. One injector didnt seat 100% and there was my yuge vac leak.

shem
A_Lonely_Potato JUL 28, 08:21 PM

quote
Originally posted by PhatMax:

Just throwing this out there but are you sure the tach is correct ? I have an issue that the tach says it idling at 2-3k when it’s not. I did install Rodney’s tach filter but still have the same prob…..I’ll have to dive into the tach itself.



mine is horribly erratic. at idle it shows about 1400, but idling in 1st itll show almost 3k. 6k is more like 4.5k, and redline is kinda where the "X1000" is

i checked mine's accuracy by driving in 5th at 55MPH, and doing the math for what engine RPM i should be, given the tire diameter, gear ratio, and speed. i used this calculator


quote

I followed your instructions and the pintle did move. So my IAC is good and working then?



the IAC itself is working then. covering the port in the TB intake will eliminate the IAC from the equation if it doesn't stall like patrick and others have said.
theogre JUL 28, 09:54 PM
Yes Tach goes wrong, speedo too. Short reason...
The Tach and Speedo have a "chip" to run the display.
Is "programed" by resistors and capacitors for numbers printed on the back to match 0-max of numbers and ark they are on.
Example: 85 miles covering nearly 300° arc on a speedo

Caps &/or resistors can "die" for several reasons and screw up the display... "chip" is still working "right" but has wrong programing now.
Many "fix" the Resistor(s) but often bad cap and gets worse because fixing/adjusting wrong part.

So don't trust either when have problems.
Use a "Shop Tach" of many types
Anything w/ GPS can check Speedo but GPS "chips" calc Speed locally and most chips lag actual speed. So only works well on roads that allow you to drive @ X speed for many minutes.
or use ECM scanner to check Tach and Speedo accuracy.