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Old 03-19-2012, 08:53 PM   #1
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My arch nemesis... Drive-ability problems :(

Having the (semi)typical surging idle problem on my 86 5.0. In park the idle will fluctuate between about 900 and 1400, sometimes it will settle after a couple mins and run at about 900-1000 for a about a minute, then go back to surging. When I put it in gear (R or D) the engine bogs down to about 400 rpm and sometimes stalls, sometimes jumps back up to 750 where it will idle fine while in gear. Once I get it to idle in drive (by tapping gas so it doesn't die) it idles nice and smooth at 750, no surging or jumping.

EDIT: This doesn't seem to happen in morning when first starting car or after sitting for long time during day. Could be only doing it in open loop fuel cylce where the 02 sensors are not adjusting anything?

EDIT #2: I also have a pretty bad exhaust leak at the header/engine on the driver side, which I have just read could possibly cause some issues because the O2 sensor is not staying heated...

I have replaced tps sensor, reset base timing and idle and the tps. Have cleaned my iac (twice), and tonight I even "borrowed" my brother's from his 87. Soaked and cleaned throttle body, spacer, iac, resealed everything, reset everything again. Checked and rechecked for vacuum leaks. Checked the injector harness ground, engine ground, body ground. All injectors are firing. Can't figure it out. Have a couple more idea's that I've read about, coolant temp sensor, air temp sensor, I have a spare ignition module that I could try (but don't believe this would help). Smog has been removed, purge canister has been removed, EGR has been removed. Car is still SD, has new ECM, plugs, wires, cap, rotor. Stock exhaust except o/r H-pipe. Auto trans. Motor is stock except for cone filter (no airbox), and above mentioned things I have deleted. A/C has been removed along with all lines, etc. Vacuum to cruise control is disconnected and pluged.

Anyone have any ideas of what to check next? Also if anyone has a link (or can explain) how the computer gets the info from what sensors, and how it controls the idle.
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Old 03-19-2012, 08:56 PM   #2
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Would did you set your tps sensor at?
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Old 03-19-2012, 09:56 PM   #3
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Re: My arch nemesis... Drive-ability problems :(

I have tried .95, .97 and .985-.99 doesn't seem to make a difference changing the setting.
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Old 03-19-2012, 10:35 PM   #4
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in the useful mustang info sticky thread there is a link on the infamous eratic idle problem and lists things to check.

i would definitly fix the header leak because your o2 sensors may be getting false readings.

---------- Post added at 10:35 PM ---------- Previous post was at 10:31 PM ----------

the speed density could be a problem if your modded.i would look into a MAF converiosn.also check really good for vacuum leaks including your intake.and make sure your o-rings on your injectors are sealing.
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Old 03-20-2012, 09:29 AM   #5
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Re: My arch nemesis... Drive-ability problems :(

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Originally Posted by Otlaw80 View Post
Having the (semi)typical surging idle problem on my 86 5.0. In park the idle will fluctuate between about 900 and 1400, sometimes it will settle after a couple mins and run at about 900-1000 for a about a minute, then go back to surging. When I put it in gear (R or D) the engine bogs down to about 400 rpm and sometimes stalls, sometimes jumps back up to 750 where it will idle fine while in gear. Once I get it to idle in drive (by tapping gas so it doesn't die) it idles nice and smooth at 750, no surging or jumping.

EDIT: This doesn't seem to happen in morning when first starting car or after sitting for long time during day. Could be only doing it in open loop fuel cylce where the 02 sensors are not adjusting anything?

EDIT #2: I also have a pretty bad exhaust leak at the header/engine on the driver side, which I have just read could possibly cause some issues because the O2 sensor is not staying heated...

I have replaced tps sensor, reset base timing and idle and the tps. Have cleaned my iac (twice), and tonight I even "borrowed" my brother's from his 87. Soaked and cleaned throttle body, spacer, iac, resealed everything, reset everything again. Checked and rechecked for vacuum leaks. Checked the injector harness ground, engine ground, body ground. All injectors are firing. Can't figure it out. Have a couple more idea's that I've read about, coolant temp sensor, air temp sensor, I have a spare ignition module that I could try (but don't believe this would help). Smog has been removed, purge canister has been removed, EGR has been removed. Car is still SD, has new ECM, plugs, wires, cap, rotor. Stock exhaust except o/r H-pipe. Auto trans. Motor is stock except for cone filter (no airbox), and above mentioned things I have deleted. A/C has been removed along with all lines, etc. Vacuum to cruise control is disconnected and pluged.

Anyone have any ideas of what to check next? Also if anyone has a link (or can explain) how the computer gets the info from what sensors, and how it controls the idle.
The guys have given you some good advice.


A leak in the exhaust before the O2 sensors will definitely cause some issues with the O2 being able to get a correct reading for your ECU to set the air/fuel mixture. Fix that first.


If your injectors have not had the O-rings and caps replaced in recent history. Do that second.


After completing the first two repairs, check your TPS. I don't expect it will have changed and some say it doesn't have much effect to set it to begin with. They claim the ECU resets itself in respect to the TPS voltage each time the car is restarted and setting the TPS voltage won't have much effect. I haven't been able to prove or disprove that theory, so I can't say for sure how much good it will or will not do. Anyways, it's better to check and set it and not need it than to ignore it and find out later it can cause problems.


The computer uses information gleaned from all of the sensors to adjust the air/fuel mixture and engine timing. I believe it does this by comparing the information it receives from the sensors to tables that are programmed into it from the factory. You should be able to test the sensors to see if they are operational or not. If you cannot find the test procedures in your Chilton's or Haynes manual, just Google search the test procedures for the particular sensor you are wanting to test.


Last, but not least - Toss that SD and convert it to MAF.
The car will be much more drivable, responsive and receptive to modifications.
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Old 03-20-2012, 11:08 AM   #6
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Thanx for info guys. Fixing exhaust leak over my lunch break . I did replace orings and caps on my injectors before putting motor in car a few months ago.
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Old 03-20-2012, 11:47 AM   #7
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Re: My arch nemesis... Drive-ability problems :(

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Thanx for info guys. Fixing exhaust leak over my lunch break . I did replace orings and caps on my injectors before putting motor in car a few months ago.
soo this is a speed density car? does it have an aftermarket cam? and wut size injectors are u using?
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Old 03-20-2012, 12:26 PM   #8
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Speed density yes. Stock cam as far as i know. Stock 19 lb injectors
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Old 03-21-2012, 02:23 PM   #9
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Changed my fuel line to one that had a shrader valve to check fuel pressure. Key on engine off it starts at 14 psi and bleeds off to about 9 and stays. Running i have 26 psi steady even when giving it throttle. Shut car off and it drops to 14 then bleeds off to 9 in about 20 seconds and holds. Has a brand new regulator (non adjustable ). ugh
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Old 03-21-2012, 07:18 PM   #10
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Its probably your throttle body if you ruined the Teflon lining around the butterfly flapper.
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Old 03-21-2012, 07:26 PM   #11
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Quote:
Originally Posted by Otlaw80
Changed my fuel line to one that had a shrader valve to check fuel pressure. Key on engine off it starts at 14 psi and bleeds off to about 9 and stays. Running i have 26 psi steady even when giving it throttle. Shut car off and it drops to 14 then bleeds off to 9 in about 20 seconds and holds. Has a brand new regulator (non adjustable ). ugh
Fuel pressure sounds a little low to me
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Old 03-21-2012, 08:04 PM   #12
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Re: My arch nemesis... Drive-ability problems :(

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Fuel pressure sounds a little low to me
That's what i was thinking too. It doesn't matter if the vacuum line is connected to the regulator or not, still the exact same thing. My sending unit is garbage anyway, so I'm just gonna replace the sending unit and pump just to make sure.

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Its probably your throttle body if you ruined the Teflon lining around the butterfly flapper.
Are you talking about the seal at the ends of the butterfly pin? Could explain it but there is no vacuum leak there so I wouldn't think thats the problem.
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Old 03-21-2012, 09:50 PM   #13
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Re: My arch nemesis... Drive-ability problems :(

Quote:
Originally Posted by Otlaw80 View Post
Changed my fuel line to one that had a shrader valve to check fuel pressure. Key on engine off it starts at 14 psi and bleeds off to about 9 and stays. Running i have 26 psi steady even when giving it throttle. Shut car off and it drops to 14 then bleeds off to 9 in about 20 seconds and holds. Has a brand new regulator (non adjustable ). ugh
The fuel pressure should be 38-40 psi at idle with the vacuum hose removed and plugged.
If not then the regulator is defective or you may have problems elsewhere in the fuel system.
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Old 03-22-2012, 11:07 AM   #14
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Im thinking its the pump. My shrader valve is in the line before the regulator so i have low pressure before the regulator. Or am i thinking wrong?
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Old 03-22-2012, 12:10 PM   #15
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Re: My arch nemesis... Drive-ability problems :(

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Im thinking its the pump. My shrader valve is in the line before the regulator so i have low pressure before the regulator. Or am i thinking wrong?
Yes, you are thinking wrong.
The regulator determines what that pressure will be if it is working correctly.
Block off the regulator and pressure at that point would skyrocket to whatever the pump was capable of producing.


However, that does not mean that the pump could not be the problem.
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Old 03-22-2012, 12:17 PM   #16
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Is the regulator supposed to hold pressure after key off also? or is that the pumps job?
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Old 03-22-2012, 01:22 PM   #17
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Re: My arch nemesis... Drive-ability problems :(

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Is the regulator supposed to hold pressure after key off also? or is that the pumps job?
It will usually hold some pressure.
The amount and duration seems to be variable as I have never observed any repeated or matching results on my cars.
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Old 03-22-2012, 07:47 PM   #18
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Quote:
Originally Posted by Trojan Horse

It will usually hold some pressure.
The amount and duration seems to be variable as I have never observed any repeated or matching results on my cars.
Im not sure if there is a bleed off time for the foxes?..I know newer cars have them,but my chilton says nothing about it when troubleshooting(or checkin) the fuel system..but if anyone knows different id like to know as well..
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