Help! Fox with idle issues

B

bbarton

New Member

Sep 11, 2026

3

0

1

Kansas City

Friday at 3:29 PM

#1

• Friday at 3:29 PM

• #1

Did an oil change last weekend and cleaned the filter. About ten minutes after letting my 93 GT warm up she through a check engine (67 O, 84 O,34 C,66 C). Changed mass air flow sensor, TPS sensor, took EGR off and cleaned. Took EVR off and conducted continuity and it checked out at 73 ohms. Kind of at a loss. Starts and runs but idle is up and down and check engine light is on. Anyone ever had this and can help me with a direction? Not great with a meter. Also, if anyone knows a shop in the Kansas City area that does good work on foxbodys i am all ears. Thanks in advance.

 

Mcmahst

5 Year Member

Jan 19, 2021

694

275

83

Laguna Woods CA, fort Mohave AZ

Friday at 4:47 PM

#2

• Friday at 4:47 PM

• #2

Did you check the vacuum at idle to verify you didn’t create a vacuum leak with your service? Up/down idle is a symptom of vacuum leak. Good luck.

 

Reactions: keel

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

6,088

4,184

183

Claremore, OK

Friday at 5:03 PM

#3

• Friday at 5:03 PM

• #3

Reset the ECU and take it for a drive. Run codes and report back.

 

Reactions: Mcmahst and General karthief

keel

Active Member

Aug 23, 2020

256

109

53

Seattle, Wa

Friday at 5:15 PM

#4

• Friday at 5:15 PM

• #4

Mcmahst said:

Did you check the vacuum at idle to verify you didn’t create a vacuum leak with your service? Up/down idle is a symptom of vacuum leak. Good luck.

Click to expand...

Second this. If you changed the air filter then you might have created a leak in the intake tubing after the MAF. The rubber parts of the stock intake tubing can crack with age, especially the ribbed part.

 

B

bbarton

New Member

Sep 11, 2026

3

0

1

Kansas City

Saturday at 10:50 AM

#5

• Saturday at 10:50 AM

• #5

Reset and took for a drive. No change. Pulled vacuum on the egr and it didn’t die or stumble at 5hg. Then turned it off and set vacuum to 10hg but it didn’t leak. Checked hoses and connection, even pulled filter off to see if that was it. Pulled vacuum line off and cleared it with brake clean and ran air through it. I want to say the egr is bad due to it not stumbling or firing when I added vacuum to it but want to confirm before purchasing another damn part.

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

6,088

4,184

183

Claremore, OK

Saturday at 7:03 PM

#6

• Saturday at 7:03 PM

• #6

So after you cleared the codes, took it for a drive, and got it up to operating temperature did you pull the codes again? If so please post up what they are.

 

B

bbarton

New Member

Sep 11, 2026

3

0

1

Kansas City

Saturday at 7:30 PM

#7

• Saturday at 7:30 PM

• #7

They were the same. Just replaced egr and sensor and got rid of 67. Still have 84 O, 34 C and 66 c.

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

6,088

4,184

183

Claremore, OK

Saturday at 9:08 PM

#8

• Saturday at 9:08 PM

• #8

Code 84 - EGR vacuum regulator circuit failure

Post in thread 'Help with code 84 please!'
https://stangnet.com/mustang-forums/threads/help-with-code-84-please.821845/post-8272949

Code 34 - EGR valve position sensor voltage is above the closed limit

Post in thread 'code 34, EGR, Slightly Off Idle'
https://stangnet.com/mustang-forums/threads/code-34-egr-slightly-off-idle.757442/post-7571037

Code 66 - MAF sensor circuit is reporting a voltage below the minimum specified test limit

Post in thread 'Code 66 Help!!!'
https://stangnet.com/mustang-forums/threads/code-66-help.900471/post-9078317

 

Reactions: Mcmahst