Idle problems

white93LE · Oct 12, 2010

Ok I know this has been asked a million times....
I have been having a high idle problem, I can not get it below 1,100-1200rpm.
I have cleaned n replace the IAC, cleaned the TB n EGR spacer, tried clocking the mass air sensor, checked TPS voltage (0.89), also tried 2 reset base idle by disconnecting the battery for 30 mins, IAC un-plugged, ect, ect...Still cant get it below 1,100. The only thing I can think of, is the TB blade is worn n getting blow-by? Besides the idle it runs great. What little mods I have include: UPR in fender cold air intake, off road h-pipe, mac equal length shorties, elect. fan, new alt., new cap n rotor etc... The motor was replaced recently, but kinda had idle problems w the old motor also. The new motor was heads, block, lower intake. Everything else stayed the same. So I assume I transfered the problem from one motor 2 the next. HELP...

Thank you

I also changed the ACT, and ran codes...codes= 94 AIR system inop, 44 AIR system inop, 13 idle speed or air bypass not controlling idle. I took the iac apart n was very clean n free moving. Did not see the iac motor moving at all. Not sure when it should move though.

jrichker · Oct 12, 2010

See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

white93LE · Oct 12, 2010

I have done 90% of whats on there an still cant figure it out...I am just tired of trouble shooting at this point...Just hoping someone had the same problem and can help.

jrichker · Oct 13, 2010

Can you do the mechanical base idle set procedure as described in the Surging Idle Checklist? I'm not talking about someone else's idea of how to set the base idle, but the exact procedure as described in the Surging Idle Checklist.

That will tell you if the problem is mechanical or computer related.

Mustang5L5 · Oct 13, 2010

Have you run the codes?

HISSIN50 · Oct 13, 2010

Mustang5L5 said:
Have you run the codes?

Bottom of post one. 44, 94, 13

Mustang5L5 · Oct 13, 2010

Damn...I looked fpr that too and still missed it.

jrichker · Oct 13, 2010

The code 13 is the clue - someone has jacked the mechanical setting up past the point where the computer can no longer control the idle.

Code 13 Key on Engine running - Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too high)

If your idle is above 725 RPM, the computer will set this code. Normal idle speed is 650-725 RPM. Higher than that may mean that you have a vacuum leak or someone has mechanically set the idle speed by use of the idle speed screw. This effectively disables to computer’s ability to control idle speed.

Like I said before, can you do the mechanical base idle set procedure as described in the Surging Idle Checklist? I'm not talking about someone else's idea of how to set the base idle, but the exact procedure as described in the Surging Idle Checklist.

white93LE · Oct 14, 2010

jrichker said:
Like I said before, can you do the mechanical base idle set procedure as described in the Surging Idle Checklist? I'm not talking about someone else's idea of how to set the base idle, but the exact procedure as described in the Surging Idle Checklist.

Yes I did. I disconnected the battery for 30 mins to clear all codes, disconnected the IAC, radio, lights, etc=off. Car was warmed up, still can not get below 1,300rpms. The idle screw can not go out any further, thats as low as it goes. I dumped almost a entire can off carb cleaner looking for vacuum leaks. NOTHING. I turned the IAC upside-down, idle got worse. Clocked the MAF, nothing. I have been playing with 87-93 stangs for 15 years, never had a problem like this. I am down to 3 things, 1) faulty IAC (doubtful, only a year old, and even if it was bad I should be able to get it below 1,300rpm with it disconnected) 2) worn Throttle body plate (never heard of them wearing but read it somewhere) 3) tight valves (doubtful, valve covers never been off this motor) The motor did sit for 2 years in a garage, and has 37,000 miles on it. But far as I know it has not been touched. This is driving me crazy........ Oh it also could be a sensor or computer.

jrichker · Oct 14, 2010

white93LE said:
Yes I did. I disconnected the battery for 30 mins to clear all codes, disconnected the IAC, radio, lights, etc=off. Car was warmed up, still can not get below 1,300rpms. The idle screw can not go out any further, thats as low as it goes. I dumped almost a entire can off carb cleaner looking for vacuum leaks. NOTHING. I turned the IAC upside-down, idle got worse. Clocked the MAF, nothing. I have been playing with 87-93 stangs for 15 years, never had a problem like this. I am down to 3 things, 1) faulty IAC (doubtful, only a year old, and even if it was bad I should be able to get it below 1,300rpm with it disconnected) 2) worn Throttle body plate (never heard of them wearing but read it somewhere) 3) tight valves (doubtful, valve covers never been off this motor) The motor did sit for 2 years in a garage, and has 37,000 miles on it. But far as I know it has not been touched. This is driving me crazy........ Oh it also could be a sensor or computer.

Did you remove the SPOUT when trying to set the base idle? With the SPOUT removed and the IAC disconnected, the computer is no longer controlling the idle. That means you have mechanical problems.

Mechanical problems break out into 3 areas

Vacuum leaks-some of them are very hard to find. Spraying flammable liquids or gases to find vacuum leaks is asking for a flash fire. They do not find leaks on the underside of gasket surfaces. Inspect the PVC valve plumbing and grommet, it is very easy for the grommet to leak or the hose to crack. The small vacuum lines are also prone to cracking and leaking.
If the lower intake manifold has been removed, there is a good chance that the gasket slid out of place then it was reinstalled. That makes vacuum leaks that suck air form the lifter valley and cannot be found without removing the lower intake manifold.

Binding throttle linkage - pop the throttle linkage off the throttle body. It will pry off using a screwdriver between the linkage and throttle arm. Check the idle and see if it changes. Try to change the idle speed by twisting or wiggling the throttle arm. Be sure you have backed the mechanical screw all the way out, almost to the point of falling out.

Throttle butterfly - if it binds or the body or throttle shaft is excessively worn, it will cause idle problems. Some throttle butterflies have a hole drilled in them to change the idle. If so, clean the area around the hole and cover it with bubble gum as a test.

white93LE · Oct 14, 2010

I double checked base idle, and yes this time I did take the spout connector out. I missed that the first time. No change.
The lower intake has never been off that I know of, the PVC seemed to fit fine when I installed it with this motor.
I kinda had a feeling it is the butterfly, but wanted to exhaust all my options before I bought a new TB.

Haus · Oct 15, 2010

If your idle goes to normal if you cover the hole in the throttle body...what does that tell me?? I had idle issues too and noticed when the hole was blocked. no more high idle and I can finally adjust the idle

white93LE · Oct 16, 2010

Haus said:
If your idle goes to normal if you cover the hole in the throttle body...what does that tell me?? I had idle issues too and noticed when the hole was blocked. no more high idle and I can finally adjust the idle

I dont have a hole in my throttle plate. Thanks for the idea tho.... I think the throttle plate just is worn n gettting blow-by....

Haus · Oct 16, 2010

white93LE said:
I dont have a hole in my throttle plate. Thanks for the idea tho.... I think the throttle plate just is worn n gettting blow-by....

haha that was actually a question from me lol I was actually curious about that since he mentioned the hole in the throttle blade

white93LE · Oct 16, 2010

Haus said:
haha that was actually a question from me lol I was actually curious about that since he mentioned the hole in the throttle blade

OK I lied it does have a hole...I forgot...haha...bought a new TB n EGR spacer for $30....Idle problem solved...It does have the TPS n IAC on it so still dont know which of the 3 it was...But who cares, idle set at 750rpm n I am happy again.....lol

jrichker · Oct 16, 2010

Remember the bubble gum trick - you may need it someday....

white93LE · Dec 28, 2010

I will keep it in mind...thanks...

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