No power steering at low RPM and dies at red lights. Are they related?

SpartanOne

Member
Sep 18, 2020
12
5
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37
Tennessee
I've searched the internet far and wide but to no avail. I just got my Mustang and it dies when coming to a stop. I.e. when applying the brakes. Also it has no power steering at all when it is at idle and I'm wondering if they could be related. Before I go checking the brake booster or taking things apart and all that I thought I would ask your opinions first. I know my way around cars generally speaking but I'm new to Mustangs so any advice would be appreciated.

It's a 2001 GT 4.6l. Here are some of the mods I thought could come in to play

Stage 2 Comp Cams
wrapped Long tube headers
Off-road X pipe
Accel coil packs
90mm intake elbow w/matching MAF
Typhoon intake manifold
21 LB injectors
Underdrive performance pulley
Full fender intake
N2MB WOT box
.
 
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Jul 11, 2020
12
1
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Franklin, TN
Surprising, that no one has responded to this question.

I’ll assume there are no trouble codes? The idle problem could be a bad idle air control valve.

No power steering could be a worn out power steering pump or as simple as low on fluid.
 

SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
Surprising, that no one has responded to this question.

I’ll assume there are no trouble codes? The idle problem could be a bad idle air control valve.

No power steering could be a worn out power steering pump or as simple as low on fluid.

I had some of the same thoughts. Power steering fluid is good so I'm assuming I'm in for a PS pump change. I may flush the fluid this weekend and see if that helps but if not a new pump goes on.

There is a check engine light on. The young man I got the car from had it set up for the track so It's pretty unwieldy for daily driving right now (clutch pedal is insanely stiff) and I'm going to remove the WOT Box he had on it as I won't be messing with it otherwise. However, from what I can tell so far all of the sensors are intact and plugged in to the exhaust. I have an OBD scanner so I'll pull the codes soon see what they say.
 
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SpartanOne

Member
Sep 18, 2020
12
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37
Tennessee
Okay, so looks like I have several things to consider regarding the car losing idle.

It is throwing all these codes:

P0174 - System Too Lean (Bank 2)
P0720 - Output Speed Sensor Circuit Malfunction
P1401 - DPFE (Differential Pressure Feedback Sensor)
P1409 - EGR Vacuum Regulator Solenoid Circuit Malfunction.
P0171 - System Too Lean (Bank 1)

so basically it sounds like I have too much air and not enough fuel based on the the 'too lean' codes. Definitely need to replace the EGR valve. The output speed seems unrelated but I'm not sure. Other than that I am not sure what the others refer too. Surely the 90mm intake elbow is too big for a non supercharged car right?
 
Jul 11, 2020
12
1
13
58
Franklin, TN
Ok. Surely, one of the gurus will chime in now.

This is how I would start:

The O2 sensors are reporting the P0171 and 0174 codes. Try working every thing else first.

Probably a sensor that’s not connected is throwing the 0720 code. that output sensor is on the transmission, driver side, toward the rear (FYI: The input sensor is also on the driver side of the trans, just forward of the output sensor.)

1409: are you sure there are no engine vacuum/exhaust leaks, particularly around the EGR valve? If the car was set up for racing, the EGR might have been deleted.

1401: should be on the side of the throttle body with a couple vacuum lines. If your throttle body is aftermarket, the vacuum line plan might be different than stock.
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
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The brake system is hydroboost, meaning it gets the source of it's assist from the power steering pump. When you press on the pedal, it loads up the pump slightly. You shouldn't have low assist at idle however. It could point to a failing pump.

You have a few things going on here however. You might want to clear all the codes and ensure the engine is able to maintain idle properly, and then troubleshoot if the pump is faulty
 

SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
Ok. Surely, one of the gurus will chime in now.

This is how I would start:

The O2 sensors are reporting the P0171 and 0174 codes. Try working every thing else first.

Probably a sensor that’s not connected is throwing the 0720 code. that output sensor is on the transmission, driver side, toward the rear (FYI: The input sensor is also on the driver side of the trans, just forward of the output sensor.)

1409: are you sure there are no engine vacuum/exhaust leaks, particularly around the EGR valve? If the car was set up for racing, the EGR might have been deleted.

1401: should be on the side of the throttle body with a couple vacuum lines. If your throttle body is aftermarket, the vacuum line plan might be different than stock.


Thanks! That is good info regarding the output sensor so I'll have to check it.

As it turns out, this car has had an EGR delete so no EGR valve, no solenoid. I Inspected the lines coming from the area but couldn't discern anything obviously damaged or anything. I am still not 100% sure of any vacuum leaks or not though. The lines that would normally go to the EGR are of course rerouted now - one is capped off and the other looks to be going in to the fuel rail/injector sensors. I attached some photos
 

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SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
The brake system is hydroboost, meaning it gets the source of it's assist from the power steering pump. When you press on the pedal, it loads up the pump slightly. You shouldn't have low assist at idle however. It could point to a failing pump.

You have a few things going on here however. You might want to clear all the codes and ensure the engine is able to maintain idle properly, and then troubleshoot if the pump is faulty

I agree. The more I dive in to this the more I realize that the power steering is the least of my worries!
 

SpartanOne

Member
Sep 18, 2020
12
5
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37
Tennessee
Okay so PCV valve seemed pretty loose and someone had sprayed some sort of goop on it (sealant of some kind). I put electrical tape around it and plugged it back in for a more snug fit. Car runs a little better and now has some power steering so that is cool. Still must have a vacuum leak somewhere though. Found a brittle fuel line that leaked when I pushed it so will be replacing that too
 
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Jul 11, 2020
12
1
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Franklin, TN
I hope your State doesn’t require an emissions test to get a tag, but I think you have a few ideas to get started.

Also, the idle air control valve or throttle body might be dirty causing a a bad idle.
 

SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
I hope your State doesn’t require an emissions test to get a tag, but I think you have a few ideas to get started.

Also, the idle air control valve or throttle body might be dirty causing a a bad idle.

No emissions checks here so car is already tagged. I did check the IAC and it appears to be brand new. I sprayed it out anyway just for good measure but no change.

So far all sensors seem to be in place so unless one is just bad I'm pretty stumped at this point. Since there is no EGR anymore that seems to be out of the equation and the throttle body, transmission and exhaust sensors all seem to be in place. There has to be another vacuum leak that I am missing. But I don't know how to find it. I know you can spray carb cleaner on a running engine near the hoses but even on a cold engine that just seems like asking for trouble.
 

2valveben

New Member
Sep 25, 2020
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I had the same issue awhile back. Thought it was a fuel issue such as a clogged fuel filter but turned out to be the IAC. The spring inside of it went missing, so I would double check just to make sure the spring is in place.
 

dr.zed

Member
May 17, 2020
16
6
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71
Nova Scotia
I've searched the internet far and wide but to no avail. I just got my Mustang and it dies when coming to a stop. I.e. when applying the brakes. Also it has no power steering at all when it is at idle and I'm wondering if they could be related. Before I go checking the brake booster or taking things apart and all that I thought I would ask your opinions first. I know my way around cars generally speaking but I'm new to Mustangs so any advice would be appreciated.

It's a 2001 GT 4.6l. Here are some of the mods I thought could come in to play

Stage 2 Comp Cams
wrapped Long tube headers
Off-road X pipe
Accel coil packs
90mm intake elbow w/matching MAF
Typhoon intake manifold
21 LB injectors
Underdrive performance pulley
Full fender intake
N2MB WOT box
.
Not sure if this is valuable at all, but your brake booster is run by your power steering pump - do your brakes work as before?

A stalling car at idle or slow speeds it has been my experience a throttle position sensor or possibly idle air was the culprit. However dirty MAF and old plugs exasperate the situation. Though my 98 ran so well with 22 year old coil packs, wires and original plugs so bad they were 0.075 gap - 120,000 kms.

Also FWIW I remember an old school drag racer saying header wrap rots our headers badly and pose a potential fire hazard. It sounds counter intuitive perhaps, but something to think about removing. I have little experience though with this.
 

dr.zed

Member
May 17, 2020
16
6
13
71
Nova Scotia
No emissions checks here so car is already tagged. I did check the IAC and it appears to be brand new. I sprayed it out anyway just for good measure but no change.

So far all sensors seem to be in place so unless one is just bad I'm pretty stumped at this point. Since there is no EGR anymore that seems to be out of the equation and the throttle body, transmission and exhaust sensors all seem to be in place. There has to be another vacuum leak that I am missing. But I don't know how to find it. I know you can spray carb cleaner on a running engine near the hoses but even on a cold engine that just seems like asking for trouble.
How much HG of vacuum are you holding?
 

dr.zed

Member
May 17, 2020
16
6
13
71
Nova Scotia
Okay so PCV valve seemed pretty loose and someone had sprayed some sort of goop on it (sealant of some kind). I put electrical tape around it and plugged it back in for a more snug fit. Car runs a little better and now has some power steering so that is cool. Still must have a vacuum leak somewhere though. Found a brittle fuel line that leaked when I pushed it so will be replacing that too
Mine was as well and I did the exact same thing and a few weeks later the tape was gone and sucked up into the PC valve!!! I went and bought a new grommet to solve it.

... I wonder... if somebody has programmed the computer and turned off a bunch of codes? It would be odd not to see a single code here...
Maybe get a spare ECM from a wrecker and try it?
 
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SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
Mine was as well and I did the exact same thing and a few weeks later the tape was gone and sucked up into the PC valve!!! I went and bought a new grommet to solve it.

... I wonder... if somebody has programmed the computer and turned off a bunch of codes? It would be odd not to see a single code here...
Maybe get a spare ECM from a wrecker and try it?

I have the same thought. This car has a WOT box and he gave me a an SCT Flash tuner with it (though I can't get it to work) so I don't know if it has a tune already or what. However, it is throwing these codes:
P0174 - System Too Lean (Bank 2)
P0720 - Output Speed Sensor Circuit Malfunction
P1401 - DPFE (Differential Pressure Feedback Sensor)
P1409 - EGR Vacuum Regulator Solenoid Circuit Malfunction.
P0171 - System Too Lean (Bank 1)

It has no EGR valve, no EGR solenoid on it any longer as it was deleted by the previous owner.
 

SpartanOne

Member
Sep 18, 2020
12
5
13
37
Tennessee
Okay guys. I've been staring at this thing for a while and something keeps looking funny. The first nice and clean image is a stock image from the internet of the 4.6l engine showing the throttle body . The second image is my car with the aftermarket throttle body and EGR delete and other things. Is it just me or is the PCV hose connected to the wrong side of the throttle body? Sorry for the crappy drawing illustrations. :( Maybe the aftermarket one is supposed to be flipped like that? Seems unlikely. I guess my concern at this point is if I swap them to find out what other damage might it do.

tempsnip.png
Vacuum2.jpg
.
 
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