Hanging Idle with Vortec ... I think I'm close

KHibbs · Mar 16, 2011

Hanging Idle with Vortech ... I think I'm close

Let me just say I have been a Mustang owner for just a short time but I have found TONS of good information on this site and it seems to have a great community. My past projects have been Jeeps with similar guys willing to help each other out.

So the issue................ hanging idle. Warm or cold, clutch in while in gear or just rev the engine and it hangs at 1500 - 1700 for about 3-5 seconds and then drops down to about 950.

I've done as much research as I think I can do on the topic and see all kinds of fixes. TPS, IAC, Vaccume leaks, kinked throttle linkage. It idles well at 950 with no surges and the TPS is at .916 volts. I did the idle reset process just in case there was something there....

Here is why I think I'm close and would like to know if anyone has any suggestions. When I disconnect the IAC it operates perfectly. It won't stay running if disconnected and I try to start the car from cold, but if it warms up and then I unplug the wires to the IAC, it drops right to 800-900 everytime. The engine has about 2000 miles since a complete rebuild and the IAC valve and motor look brand new. I have taken them off and sprayed the valve with injector cleaner and it looks really clean. The gasket is new as well. The wires also have plenty of slack.

Besides running out and dropping the cash on a new IAC and/or IAC motor right away (because I just hate throwing parts at something without ruling out the problem) are there any suggestions as to ways I can confirm what is wrong?

Current Induction:
UPR Boostmaster pipe
Vortech V2 - Set for 8lbs
70mm BBK Throttle Body
GT40 Upper/Lower Intakes

Thanks so much for any suggestions as the nice weather is FINALLY starting to show itself in New England and I really want to resolve this issue.

K

4rdnut · Mar 16, 2011

Ford engineers purposely programmed the eec iv computer to hang the idle, they claim it's for lowering emissions by burning off excess fuel. You will need a computer geek to reprogram the computer to fix that hanging idle. My idle hangs just like yours, but i have an automatic trans which isn't as bothersome as a manual with the clutch. There are people who sell iac gaskets with a smaller hole on the intake side and claim it lessens the hanging idle, don't fall for it , they don't work, the eec iv computer is to smart for that. I made a iac gasket with no holes and kept the iac plugged in and the eec iv computer threw in extra timing to hang the idle. The vss sensor also has a part in the hanging idle, sending a signal to the computer, if you remove the vss sensor speedo gear thinking that will cure the hanging idle, the computer will stall your engine when you come to a braking stop. The only real cure is going carbed.

2000xp8 · Mar 16, 2011

Hibs, are you suggesting it does it when you first start the car, or all the time, like if you stopped at a stoplight?

larrym1961 · Mar 16, 2011

4rdnut said:
Ford engineers purposely programmed the eec iv computer to hang the idle, they claim it's for lowering emissions by burning off excess fuel. You will need a computer geek to reprogram the computer to fix that hanging idle. My idle hangs just like yours, but i have an automatic trans which isn't as bothersome as a manual with the clutch. There are people who sell iac gaskets with a smaller hole on the intake side and claim it lessens the hanging idle, don't fall for it , they don't work, the eec iv computer is to smart for that. I made a iac gasket with no holes and kept the iac plugged in and the eec iv computer threw in extra timing to hang the idle. The vss sensor also has a part in the hanging idle, sending a signal to the computer, if you remove the vss sensor speedo gear thinking that will cure the hanging idle, the computer will stall your engine when you come to a braking stop. The only real cure is going carbed.

That is interesting to know about the the programed hanging idle, I thought I was the only one that had that annoying problem!

jrichker · Mar 17, 2011

See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! 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.

KHibbs · Mar 17, 2011

I'm confused about the answer of the ecm being programmed to do this from that factory as I remember stock 5.0s from the past that didn't do this. I've also read that there can be an issue with a pressure release valve from the Vortech... that is why I posted the Vortech in the post title.

2008p8 - Just to clarify (and I guess this is standard with any 5.0) if you try to start the car when cold and you don't have the IAC plugged in, it won't idle. I can keep my foot on the gas for a minute or two to get some temp in the engine and then it will idle ok and the rpms drop right down to 800 or so like they should.

It also "hangs" all the time when the IAC is connected. Stoplights, in between shifts, moving, not moving .. you name it.

jrichker - I will go through the list you posted and see what I can find. I thought I was close to a finding a solution when I narrowed it down to the problem going away when the IAC plug is disconnected.

I'll do some research this weekend and report back....thought I was right there..

90lxcoupe · Mar 17, 2011

I had this problem for a while with my car and one day it just went away, i know this dosent help, but i tried jsut about everything to fix it and had no luck, and then one day, it just starts idling right

2000xp8 · Mar 17, 2011

KHibbs said:
I'm confused about the answer of the ecm being programmed to do this from that factory as I remember stock 5.0s from the past that didn't do this. I've also read that there can be an issue with a pressure release valve from the Vortech... that is why I posted the Vortech in the post title.

2008p8 - Just to clarify (and I guess this is standard with any 5.0) if you try to start the car when cold and you don't have the IAC plugged in, it won't idle. I can keep my foot on the gas for a minute or two to get some temp in the engine and then it will idle ok and the rpms drop right down to 800 or so like they should.

It also "hangs" all the time when the IAC is connected. Stoplights, in between shifts, moving, not moving .. you name it.

jrichker - I will go through the list you posted and see what I can find. I thought I was close to a finding a solution when I narrowed it down to the problem going away when the IAC plug is disconnected.

I'll do some research this weekend and report back....thought I was right there..

I used to have the hanging idle issue way back years ago.
Turned out to be the tps.

f8tlfiveo · Mar 17, 2011

I bought a quarterhorse and had someone with experience from EEC tuning figure out the problem.. Car runs better than it ever did.. Worth every penny.. Most guys on that site are pretty helpful.

KHibbs · Mar 17, 2011

2000xp8 said:
I used to have the hanging idle issue way back years ago.
Turned out to be the tps.

I haven't gone through all of the notes in the link that jrichker posted so I may be jumping ahead and this info is in there but...

The TPS is set at .916 volts and the idle is steady at about 950 so I assume that it is working properly.

Is there a way that you can test the TPS or the IAC independently to check for proper operation before just replacing them?

Thanks,

KHibbs

jrichker · Mar 17, 2011

See http://www.stangnet.com/mustang-forums/825424-adjusting-your-tps-0-98v-not-necessary.html for help testing & setting the TPS.

KHibbs · Mar 17, 2011

jrichker said:
See http://www.stangnet.com/mustang-forums/825424-adjusting-your-tps-0-98v-not-necessary.html for help testing & setting the TPS.

EXCELLENT...thank you. I read that a week or so ago (so I know I didn't have to be at .98 or .99 for the TPS) but I must have forgotten the part about testing the TPS was in there. I will test the TPS this weekend and hopefully cross that off the list as a possible culprit.

I am misleading myself by thinking that it is IAC related just because it goes away when the unit is unplugged? Maybe I need to research the IAC a bit more to understand exactly how it operates.

Thanks guys.. keep the suggestions coming and I'll check off the TPS tomorrow or Sat and report back.

KHibbs

4rdnut · Mar 18, 2011

The hanging idle is programmed into the computer. The computer controls the iac valve and your idle with help from the vss (vehicle speed sensor) which is bolted to your transmission, there is a parameter in the computer called the dash pot delay, put in there by ford engineers because in fords mind, hanging the rpms up for 3-5 seconds burns off excess fuel and emissions, a computer tuner can lessen the delay so the rpm's drop quicker. Do an internet search and type in eec iv system mythology and another internet search type in eec iv codes troubleshooting database, you will find the information you need.

f8tlfiveo · Mar 18, 2011

+1 on dashpot.... That's exactly what I did... Idles great... No surging.... No hanging.. Messin around with iac, tps, only worked for a little for me. The stupid surging would always come back... Very frustrating.

2000xp8 · Mar 18, 2011

KHibbs said:
EXCELLENT...thank you. I read that a week or so ago (so I know I didn't have to be at .98 or .99 for the TPS) but I must have forgotten the part about testing the TPS was in there. I will test the TPS this weekend and hopefully cross that off the list as a possible culprit.

I am misleading myself by thinking that it is IAC related just because it goes away when the unit is unplugged? Maybe I need to research the IAC a bit more to understand exactly how it operates.

Thanks guys.. keep the suggestions coming and I'll check off the TPS tomorrow or Sat and report back.

KHibbs

The reason it's not the IAC is because there is something else telling it to adjust the idle, because it's not actually a sensor, it doesn't read anything.

Having it tuned out of the computer is just a band aid on a real problem, i would not consider that a solution.

Run the codes like jrichker suggested.
You'd be surprised what could come up as a problem, i wouldn't doubt that it's even the vss.

BlackGT89 · Mar 18, 2011

Don't forget to check your 10 Pin Connectors...

http://www.stangnet.com/mustang-forums/828919-intermittent-high-idle.html

Hanging Idle with Vortec ... I think I'm close

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