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Discussion Starter · #1 ·
So I have a 2001 (it might be a 2000, i cant remember) 3.8 5spd mustang that 75% of the time the idle will hang at 1500+ rpm for 10-15 seconds when clutch depressed and coasting or stopped a light. Eventually the idle will fall to normal 600-700 if I do nothing. If I turn the car off for 5 seconds then restart it when coasting or stopped at light the idle issue is fixed for the remainder of the drive. The car generates no displayed or stored codes from OBD port.

I have replaced the DPFE, I originally suspected my EGR system was not closing completely at idle but I have went so far as to create a block-out plate to eliminate the EGR port from the intake for testing purposes and it had no effect on the high idle issue. The egr system has since been returned to its factory condition appears to be working normally.

I have back probed the TPS .95 at idle ~ 4.5 at WOT. I have back probed the MAF (normal). The car stalls when TPS connection is removed, car continues to run with MAF connection removed.

Again shuting the car off and restarting it fixes the idle problem until i let it set for an extended time!?

PLEASE help, i dont know what to do with this thing anymore, it has been doing this for 7 months.


EDIT: I have cleaned the MAF & replaced the IAC, no help
 

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Have you checked your IAC? Clean it if you haven't already.
 

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Then I don't know where to begin, you checked most of the things that could cause it. Maybe clean your CAI and air filter and your MAF.
 

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Discussion Starter · #5 ·
I have cleaned the MAF with appropriate cleaner. CAI? is that cold air intake? if so the ducting appears to be sufficiently clean. THANKS for suggestions.
 

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doesnt the v6 naturally have a very irratic idle? mine idles about 1200 when i start it up for a bit but then goes down to normal within about 10-15 sec and stays normal the rest of the drive.
 

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Discussion Starter · #7 ·
It may idle high when cold, but mine does this high idle business all of the time. Well unless i shut it off for a second or two then it works fine again?
 

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Yeah, the cold air intake is what I meant. Well I assume you cleaned out the throttle body too? All the hoses are in good condition? I had idling issues and it was a simple air filter clean for me, so you can't be far away in finding the problem.
 

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Discussion Starter · #9 ·
I have went so far as running no air cleaner for a bit (has one of those stupid KN deals in it) I have replaced every vacuum line on the engine I can find. I have propane vacuum leak checked the upper manifold several times. I may soon simply invest in a for sale sign and stick the the classic mustangs.
 

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doesnt the v6 naturally have a very irratic idle? mine idles about 1200 when i start it up for a bit but then goes down to normal within about 10-15 sec and stays normal the rest of the drive.
Yeah, just letting her warm up:hihi:
 

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I have went so far as running no air cleaner for a bit (has one of those stupid KN deals in it) I have replaced every vacuum line on the engine I can find. I have propane vacuum leak checked the upper manifold several times. I may soon simply invest in a for sale sign and stick the the classic mustangs.
Well, if it comes down to that, then good luck with the sale man. I've ran into some issues with my 01 V6 before and was fortunate to find the issue and fix it. Hope you find out what it is. It makes for a good daily driver car.
 

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hey well my 2000 v6 has a rough idle sometimes, well what i did was replaced the idle air controller sensor.an let the car warm up everytime u start let it warm up for 3-5 minutes.try it maybe it would work with yours to.:bigthumbsup
 

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So I have a 2001 (it might be a 2000, i cant remember) 3.8 5spd mustang that 75% of the time the idle will hang at 1500+ rpm for 10-15 seconds when clutch depressed and coasting or stopped a light. Eventually the idle will fall to normal 600-700 if I do nothing. If I turn the car off for 5 seconds then restart it when coasting or stopped at light the idle issue is fixed for the remainder of the drive. The car generates no displayed or stored codes from OBD port.

I have replaced the DPFE, I originally suspected my EGR system was not closing completely at idle but I have went so far as to create a block-out plate to eliminate the EGR port from the intake for testing purposes and it had no effect on the high idle issue. The egr system has since been returned to its factory condition appears to be working normally.

I have back probed the TPS .95 at idle ~ 4.5 at WOT. I have back probed the MAF (normal). The car stalls when TPS connection is removed, car continues to run with MAF connection removed.

Again shuting the car off and restarting it fixes the idle problem until i let it set for an extended time!?

PLEASE help, i dont know what to do with this thing anymore, it has been doing this for 7 months.


EDIT: I have cleaned the MAF & replaced the IAC, no help
I think you are reading more into this than what it is. Our flywheels are heavy, and the continuation of rotational mass will take that long for the idle to decrease when you depress the clutch. If you had an aluminum flywheel, it would go down quicker. The only other thing I would say to do is take off your throttle body and clean it and use some fine grit sandpaper to ensure the butterflies are closing. They can bind, and this happens alot on my nitrous car after track runs......

If you are not getting codes and the motor is operating within parameters, it is fine.......
 

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Discussion Starter · #14 ·
I think you are reading more into this than what it is. Our flywheels are heavy, and the continuation of rotational mass will take that long for the idle to decrease when you depress the clutch. If you had an aluminum flywheel, it would go down quicker. The only other thing I would say to do is take off your throttle body and clean it and use some fine grit sandpaper to ensure the butterflies are closing. They can bind, and this happens alot on my nitrous car after track runs......

If you are not getting codes and the motor is operating within parameters, it is fine.......
I see your point however, it behaves differently now than when I purchased the car. And if I shut the car off and restart it while it is at high idle at a stop sign it will resume normal idle speed and keep normal idle speeds at all further stop signs.

If fact, if i dont depress the clutch soon enough when slowing down and let the transmission drag the engine RPMs down to say 800 before depressing the clutch at a stop sign when I do press the clutch the RMPs will quickly jump to 1500-1600 and stay there for 15-20 seconds before returning to 700ish RPM idle.....

I am positive there is something causing the idle to hang high. I dont think it is a mechanical problem due the the electrical reset fixing the issue.

I just drove around today with a lead on the TPS in attempt to confirm that the TPS is not at fault. .95v at normal idle and .95v at high idle. TPS is out of the question.
 

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I think you are reading more into this than what it is. Our flywheels are heavy, and the continuation of rotational mass will take that long for the idle to decrease when you depress the clutch. If you had an aluminum flywheel, it would go down quicker. The only other thing I would say to do is take off your throttle body and clean it and use some fine grit sandpaper to ensure the butterflies are closing. They can bind, and this happens alot on my nitrous car after track runs......

If you are not getting codes and the motor is operating within parameters, it is fine.......
no way.

our flywheels are not heavy enough to keep the engine spinning at a steady high rpm for 10-15 seconds after letting the clutch out. even if the flywheel was heavy enough to cause it, (which believe me it's not, ive held my stock one) it wouldnt cause it to intermittently hang the rpms high, it would do it every single time, and we would see more threads about this issue than V8 swaps and exhaust suggestions. i do have an aluminum flywheel, and it does help a little, but when my MAF gets dirty, the rpms will still hang intermittently and the idle will be high.

OP:
if you're not getting codes, it's most likely your MAF, or maybe the IAC. those are the usual culprits.
this same issue starts happening to my car every 6-7 months or so, and it goes away after i clean the MAF.
when it gets real bad, my rpms would intermittently hang (or even increase) between shifts, and when slowing down to a stoplight, the rpms will hang for 20 seconds or more at as high as 3k. like you mentioned, restarting the engine temporarily remedies the problem. that is NOT normal.
also, even when i had all those symptoms i just listed, no CEL.

try unplugging the MAF and see if the car runs like sh**.
also, if you have a tuner or a decent OBDII scanner with live data capabilities, you can rpm test the MAF sensor. At different rpm's, the MAF sensor is supposed to be reading a specific amount of voltage. for example, at idle, between .7v and 1.0v, and at 2,500 rpms, between 1.2v. and 1.7v. that's not the correct specification, you'll have to look it up. but that is where i would start.
 
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Mine does this too. :headscratch:
I recently installed a CAI and I cleaned my MAF. Where is the IAC located so I can take a look at it? Thanks.
 

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Mine does this too. :headscratch:
I recently installed a CAI and I cleaned my MAF. Where is the IAC located so I can take a look at it? Thanks.
It is located on the left side of the TB when you face it.
 

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Discussion Starter · #19 ·
I have completely removed the throttle body and extensively cleaned it and installed with a new gasket. The MAF does put out correct voltage at idle and voltage increases with RPS as haynes manual suggest it should. I have not yet tried to capture MAF voltage with a load on the engine. I have cleaned the MAF with electrical cleaner. I appreciate all the help thus far, someday I will find the magic dodad that is causing all these problems.

Anybody know how to test the IAT probe? I know it is in the same assy as the MAF and has its own pins in the MAF harness but I dont know what the outputs should be, it must be a resistance function.
 

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Discussion Starter · #20 ·
no way.

our flywheels are not heavy enough to keep the engine spinning at a steady high rpm for 10-15 seconds after letting the clutch out. even if the flywheel was heavy enough to cause it, (which believe me it's not, ive held my stock one) it wouldnt cause it to intermittently hang the rpms high, it would do it every single time, and we would see more threads about this issue than V8 swaps and exhaust suggestions. i do have an aluminum flywheel, and it does help a little, but when my MAF gets dirty, the rpms will still hang intermittently and the idle will be high.

OP:
if you're not getting codes, it's most likely your MAF, or maybe the IAC. those are the usual culprits.
this same issue starts happening to my car every 6-7 months or so, and it goes away after i clean the MAF.
when it gets real bad, my rpms would intermittently hang (or even increase) between shifts, and when slowing down to a stoplight, the rpms will hang for 20 seconds or more at as high as 3k. like you mentioned, restarting the engine temporarily remedies the problem. that is NOT normal.
also, even when i had all those symptoms i just listed, no CEL.

try unplugging the MAF and see if the car runs like sh**.
also, if you have a tuner or a decent OBDII scanner with live data capabilities, you can rpm test the MAF sensor. At different rpm's, the MAF sensor is supposed to be reading a specific amount of voltage. for example, at idle, between .7v and 1.0v, and at 2,500 rpms, between 1.2v. and 1.7v. that's not the correct specification, you'll have to look it up. but that is where i would start.
I have run the car at idle with MAF unplugged and noticed no change in idle quality, though it idles fine on initial startup usually. Typically the problem does not present itself untill I have driven for 2-3 minutes then the high idle shows itself.

So just to clarify you have had the same issue and restarting it does fix the idle issue for a little while? I have cleaned the MAF but I will replace it with a new one if I have good reason to believe that is the cause. I am sure those things are pricey.
 
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