Hello i'm new here and have had my 90 Fox vert for about a year and a half, i'm currently having a slight idle surge and a hesitation when I goose the throttle. The hesitation is present when at idle and I rev it and when I drive and romp on it, as for the idle it surges about 100 rpm maybe a hair more and smooths out in gear but I can feel it surge as I let the brake go but don't give it any throttle. I know this is a common issue and I have gone through the Idle surge checklist and believe I may have narrowed it down, just looking for some of the veterans here to help me get this solved! Some info on the car it is a 90 convertible with 5.0 and an AOD and about 52k mi. I have done several mods and just a note this problem was not present before these mods. Mods the car came with shorty headers, cat back exhaust, CAI into the fender, 3:73 gears, lowered, mods I added before the problem shift kit, full tune up cap, rotor, wires, plugs, fuel filter, air pump delete, under drive pulley's, X-pipe no cats, 200 amp alternator, B&M hammer shifter, BBK 70mm throttle body, SCT chip. the mods now added that the car now has these issues GT40X heads got a great deal on them new, explorer upper and lower intake gasket match porting, 24lb Ford Racing injectors, BBK MAF 76mm matched to the injectors, MSD coil new, MSD distributor bought used! new MSD cap and rotor, EGR deleted 1:7 full roller rockers, 180 high flow stat, 94 mustang fuel rails, stock but new FPR, NGK v-power plugs, Ford Racing 9mm wires, aluminum radiator, and dual electric fans and re-flashed the SCT chip. I have checked and set timing at 14deg with spout out, fuel pressure is steady and about 39lbs at idle with vac off, base idle has been reset numerous times to try to deal with the idle issue, the IAC is stamped Ford and is what came with the car, I purchased a supposed Motorcraft one and it was terrible caused a very high idle and made the car lunge when put in gear, so sent that back, TPS was replaced with the throttle body, TPS voltage is set at .97 that seems to make the car the happiest I have tested all areas for a vacuum leak found one and fixed it, the car is currently running 17-18 in vac at idle and the idle is about 800rpm vacuum fluctuates from 17-18 as the idle goes up and down I've noticed the idle is smooth for about 20sec or so then raises and then smooths out again also car is running a little rich at idle but seems reasonable . I'm feeling at this time that the issue could be the TPS but it seems to have the correct voltages and at WOT it measured over 4volts, also thinking it could be the pick up in the distributor. I did get that used on E-bay it looked like new but have heard I should have stuck with the stock one but that is long gone now! I did get a backup TFI module and switched it out and no help! So thats it in a nutshell I checked all grounds and have been over the check list also pulled codes KOEO I got 15/85 the 15 i believe is due to the chip and 85 is due to the charcoal canistor disconnected and clear on the KOER any help is appreciated and thanks in advance.
Newbie Needs Help With Slight Idle Issue And Hesitation
- Thread starter DanstangLI
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mikestang63
SN Certified Technician
What happens when you remove the chip? Are you supposed to have the timing set to stock -10 degrees with it?
I havent tried to remove the chip, I felt that the chip was not an issue prior to the other mods, but now that you mention it I did have it re-flashed for the new mods so I guess it could have an issue. I will remove it tomorrow and see what happens, and as for timing I just went over the paperwork that came with the chip and it states the chip assumes 10 deg of timing so I will readjust the timing tomorrow and see if that makes any difference as well. Thanks for the reply and hope this will help the situation!
Ok reset the timing to 10 deg and no noticeable difference, then I removed the chip and the idle is smoother has minimal fluctuation and dropped to about 700 rpm down from 850 or so with the chip! The hesitation is still there however when I goose the throttle. I think I will contact American Muscle and see what they say about the difference in the idle without the chip but I'm still at a loss on the hesitation. Any other input or suggestions would be greatly appreciated. Thanks
When you tested the TPS, did you just check the idle and peak voltage, or did you slowly open the throttle to ensure a smooth operation all the way through the motion? Look for flat spots or erratic jumps in the voltage curve as you open the throttle blade.
Couldn't hurt to pull the EGR valve and IAC solenoid off and clean the carbon deposits from them to ensure they're operating freely.
Also, I would give the MAF elements (front and rear) a thorough, but gentle cleaning with a cotton swab and some rubbing alcohol. These can become contaminated over time and slow the response of the meter.
How old are your O2 sensors? They should probably be replaced every 100,000km or so.
Couldn't hurt to pull the EGR valve and IAC solenoid off and clean the carbon deposits from them to ensure they're operating freely.
Also, I would give the MAF elements (front and rear) a thorough, but gentle cleaning with a cotton swab and some rubbing alcohol. These can become contaminated over time and slow the response of the meter.
How old are your O2 sensors? They should probably be replaced every 100,000km or so.
mikestang63
SN Certified Technician
Do a base idle reset with the chip out. Disconnect the battery for about 1/2 an hour with the headlight switch on. See if that clears it up.
Thanks for the input I no longer have the EGR valve and I did clean the IAC solenoid just recently when I re installed the original, I also cleaned the MAF element as well I had just oiled a new air filter and installed it and thought the oil may have coated the sensor, but that made no significant difference. The O2 sensors are brand new had them installed with the X-pipe and only put a few miles on them before I did the top half of the motor. As for the TPS I will recheck the voltage as you stated and make sure throught the throttle movement the voltage doesn't get erratic. Thanks again for the help and any other input is greatly appreciated!
jcgafford
10 Year Member
Ok did the base idle reset and set the TPS to .97.7 volts and the idle is much smoother but still have the flat spot when I goose it, i'm assuming the chip is causing my idle issue at this point but not sure on the flat spot, any other thoughts?
Just an update I went back to the TPS and checked the voltage through the range of the throttle plate motion and I found at about 3.2 volts or so my digital meter went to OL and then went to the voltage right were it left off. I'm not very knowledgeable about volt meters but doesn't that mean there is a spike in voltage at that moment? The voltage is consistent through the rest of the movement and I rechecked it several times and it does the same thing at that moment every time! Do you think the TPS has an issue? Any thoughts are greatly appreciated
Ok still working on this and just posted about the TPS voltage findings I also wanted to let you know I went and pulled the plugs and found the gap was ridiculously set at about .055" maybe a little more! I don't know what I was thinking or how much I drank the night before but that has been corrected and I reset them to .045", from what I have read that should be adequate for my setup I hope. I did start it up and feel that helped with the flat spot on the throttle but it isn't 100%, I also played around with the throttle and held it at 2000rpm and noticed it almost feels like a slight miss is there, it held the rpms but it wasnt totally steady. Any thoughts would be really appreciated i'm leaning to ignition again but not certain on it. Also on the plugs they were looking a little on the lean side showing a slight whitening but not terrible I also have a spark plug boot on the #4 cyl that is deteriorating! The wires are Ford Racing 9mm and literally brand new very disappointed I wrapped it with electrical tape I dont believe it is causing any arcing but will have to get a new set any recommendations? Thanks again for all your help
mikestang63
SN Certified Technician
I have the GT40X aluminum heads what should it be for them? also what do you think of Livewires for spark plug wires?
mikestang63
SN Certified Technician
Autolite 104 or 764 plug gapped at .50-.52 . For wires I would recommend Taylor wires # 84258
On a n/a setup the larger the gap the more power you will make, assuming your ignition system can maintain the spark. Closing the gap will hurt performance and fuel economy.
On a n/a setup the larger the gap the more power you will make, assuming your ignition system can maintain the spark. Closing the gap will hurt performance and fuel economy.
Great thanks for the info going to order a set of Taylor wires and going to just replace the TPS due to the weird voltage I got and see where that gets me
Forgot to ask, on the Taylor wires I have shorty headers will those boots clear the tubes? The Ford racing wires on there are 90 deg boots and the #4 cyl has a tube that is close and the heat deteriorated it. I'm concerned the Taylor's are listed as 135 deg boot, what's your thoughts?thanks again can't wait to get this pony back to where it needs to be
Do a cylinder balance test to locate dead or weak cylinders.
Cylinder balance test: use this to find dead or weak cylinders:
Revised 25 March 2012 to add necessity allowing the KOEO tests to finish before starting the engine and the need for a properly functioning IAB/IAC to run the cylinder balance test.
The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.
Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
Be sure to turn off the A/C clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.
Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems
Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Cylinder balance test
If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure
Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.
How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.
With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.
I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.
A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.
PM me for details on how to build your own blow down type compression tester.
Cylinder balance test: use this to find dead or weak cylinders:
Revised 25 March 2012 to add necessity allowing the KOEO tests to finish before starting the engine and the need for a properly functioning IAB/IAC to run the cylinder balance test.
The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.
Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
Be sure to turn off the A/C clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.
Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems
Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Cylinder balance test
If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure
Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.
How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.
With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.
I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.
A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.
PM me for details on how to build your own blow down type compression tester.
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