[chrisb24]

I have a 1988 ford mustang GT with the 5.0 HO motor with cold air intake . When acceleratin the throtle the car popps and lugs but when I get the car out on the open road at around 65 to 70 mph the car smooths out and does not popp nor does it lug what could be the problem???

[ddarkslayer]

lean mixture

[88stanglx]

Also, when i had that problem with my 88, it ended up being the diode on the ICU harness right before the distributor. Some people call it the lego but i ended up pulling that off and now it runs fine, i just have to find a new one. Also another common cause, which some people overlook, is loose battery cable connections or a bad battery. If not enough energry is getting to the computer and the alternator cant supply enough energy to everything the idle will be effected.

[jessemachone]

Originally Posted by ddarkslayer I can't even start up my car with the IAC unplugged

mine will start then die immediately with the IAC unplugged.

[ddarkslayer]

Originally Posted by jessemachone mine will start then die immediately with the IAC unplugged.

I just solved my problem. If you try to start up the motor with the IAC off and it wont start up, try starting the motor up and disconnecting the IAC motor when the motor is running and warmed up. if its in the range of 550 rpm then you need to turn the idle screw up to 600, 700 RPM. Shut the motor of and disconnect the negative terminal of the battery for a minute. Plug it back in with the IAC disconnected. It should start up with no problems what-so-ever. Start checking the TPS and you want to get a spec of .88 through 1.0 volt. when I checked mine after turning the Idle screw it was 1.2 so I had to drop it.

So the biggest thing was that the throttle blades where completely closed and the IAC was working to hard and couldn't keep up and not to mention that the TPS was out of range.

The idle surge symptoms happen once the motor warms up

[jessemachone]

Originally Posted by ddarkslayer I just solved my problem. If you try to start up the motor with the IAC off and it wont start up, try starting the motor up and disconnecting the IAC motor when the motor is running and warmed up. if its in the range of 550 rpm then you need to turn the idle screw up to 600, 700 RPM. Shut the motor of and disconnect the negative terminal of the battery for a minute. Plug it back in with the IAC disconnected. It should start up with no problems what-so-ever. Start checking the TPS and you want to get a spec of .88 through 1.0 volt. when I checked mine after turning the Idle screw it was 1.2 so I had to drop it. So the biggest thing was that the throttle blades where completely closed and the IAC was working to hard and couldn't keep up and not to mention that the TPS was out of range. The idle surge symptoms happen once the motor warms up

Word, I bet that is the same issue with mine!!! I think the screw is all the way backed out... thanks for shedding the light.

[ddarkslayer]

Originally Posted by jessemachone Word, I bet that is the same issue with mine!!! I think the screw is all the way backed out... thanks for shedding the light.

I know if I didn't no body would

[895.sloGT]

hey i tried all of this but im still getting the surge however i noticed that if i pump the brake the surge goes away. is that a vacuum leak and if it is will the leak cause the surge? thanks

[jessemachone]

cap off the line going to the brake booster and try it again. Many times the little vacuum manifold on the drivers side above the brake booster gets cracked and will leak.

[895.sloGT]

thanks ill give it a try

[holset35]

TPS get a new one to just check it then take it back

[fogged306]

Originally Posted by 1slo5.0 The TPS is located directly on top of the throttle body and is adjusted by loosening the two phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small drill bit or small file to achieve the desired reading. The spec range for Key On is from .88 to 1.0 volt; shoot for the .90 to .98 volt. Make sure voltage reaches/exceeds 2.71v at WOT.

Just a correction on this part. The TPS min-max values with the throttle plate closed are between .5V and 1.19V. Anywhere in between there and your TPS sensor is fine. At WOT, you want to be 2.71V above your value with the throttle plate closed.

Example: if you have a value of .87V with the throttle plate closed, you need a value of 3.58V or greater at WOT.

[jcftw]

Thanks for the info. New here and this is just the kind of stuff I'm looking for.

[Squires67]

Hello out there
I am having a problem fith my 5.0 and looking for a lil help
The stang has been sitting for about 2 yrs occasionally getting started ive just recently had the time and $ to get it back out
it starts fine but surges while at idle im pretty sure thats a sensor but when i rev it up it sounds like it loaded up and smokes black smoke
it has an electric fuel pump on it and when you turn it off it clears up and runs fine. Could the fuel pump be flooding it out? and if so it is the same pump that has been on it for the last 5 yrs why would it start doing that?

[khern1]

hey guys i did this and i backed the idle screw back and nothing happened its still idleing at 1000rpm and i backed the idle screw all the way out to the point where i just took it off lol and its still at 1000rpm tell me what u think guys

[1NVERTED5.0]

Originally Posted by khern1 hey guys i did this and i backed the idle screw back and nothing happened its still idleing at 1000rpm and i backed the idle screw all the way out to the point where i just took it off lol and its still at 1000rpm tell me what u think guys

TPS

[moneymo]

Thanks for this info. I took my EGR off and bored my engine and put a mild cam on it. It started idling low but would seem as if it were about to turn off and sometimes does when im on a red light so i constanly give it gas. Im thinking the underdrive pulleys are killing the stock alternator. Could the same adjustments help my idle problem @1slo5.0

[moneymo]

Thanks for this info. I took my EGR off and bored my engine and put a mild cam on it. It started idling low but would seem as if it were about to turn off and sometimes does when im on a red light so i constanly give it gas. Im thinking the underdrive pulleys are killing the stock alternator. Could the same adjustments help my idle problem @1slo5.0

[brimmer555]

My 89 GT starts alittle weak at first and I have noticed the battery gauge is low when I start it up and it always idles for a minute and then dies. but if i rev it a bit and then go and it has been running for a little while the battery gauge is in the middle and it doesn't try to stall at all.

I think something is draining the battery while it sits because I have this problem every time I start it up, if it hasn't been running for a while.

I have no clue what could be draining it though?

[brimmer555]

Originally Posted by 1slo5.0 Idle issues are common on these cars, especially 5-speed cars. EGR Valves, Idle Air Bypass solenoids and Throttle Position Sensors are common causes. A bad connection with the 10 pin (salt and pepper shakers) black and white engine electrical connectors can also cause poor idle quality. To ensure a good connection on the 10 pin connectors a little modification can be done which is fairly easy and will cure some surging and hanging idle issues on 86-93 Mustangs and should be the first thing done when tackling any idle issues. 10 Pin Connector modification: 1. Take the 10 pin connectors apart (salt and pepper shakers). 2. use a pick like tool to spread the male terminals open more so they make better contact. In the center of each male terminal there is a small seam and seams down the sides of the terminal which allows you to spread them open. 3. Apply some dielectric grease to the terminals 4. Plug the connectors back in. Throttle Position Sensor (TPS) adjustment: Without the proper adjustment, the throttle position sensor (TPS) will give the computer false reading as to the exact throttle opening. A false reading will limit wide open throttle performance. A voltage reading must be taken using a digital volt/ohmmeter (DVOM) with the Key On/Engine Off and with the Key On/Engine Running. The TPS is located directly on top of the throttle body and is adjusted by loosening the two phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small drill bit or small file to achieve the desired reading. The spec range for Key On is from .88 to 1.0 volt; shoot for the .90 to .98 volt. Make sure voltage reaches/exceeds 2.71v at WOT. Incorrect Throttle Position Sensor (TPS) voltage will result in reduced performance including a possible hanging/surging idle. The best way to take a TPS voltage reading is by using two safety pins through the wires coming from the sensor. The positive lead is attached to the green wire, while the negative goes to the black wire. Always ground the meter through the sensor's black wire. This gives a direct, and more accurate ground into the computer. Resetting the base idle: Clear the computer's idle memory by disconnecting the battery for 20+ minutes. -Disconnect the Idle Air Bypass solenoid -Reconnect battery -Start engine and set idle speed to desired RPM with idle screw on throttle body -Turn off engine and reconnect the air bypass solenoid -Set TPS voltage between 0.90 - 0.95 volts with a digital volt meter -Start engine and let it idle for 2 minutes with no accessories on. -Turn off engine for two minutes -Start engine again and run for 2 minutes with every accessory turned on. -Turn engine off again.

Thanks for the great info!!!!!