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Old 01-27-2014, 12:32 PM   #1
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Question Idle issue??

I have an 88 mustang 5.0 lx and the idle does this. As you can see it bounces. It does this not only at night with the headlights on but it also does it during the day with accessories off. It's bouncing and it causes my car to even misfire at times under a medium to light load. What could this be? By the way the noise in the background is my blinker.
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Old 01-27-2014, 03:59 PM   #2
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Could be timing is off, could be a spark plug not firing...need more info, what else have you done to car?
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Old 01-27-2014, 04:15 PM   #3
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Check your charging system. Voltage regulator on the alternator, belt tensioner and belt condition.

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Old 01-27-2014, 04:39 PM   #4
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Could be timing is off, could be a spark plug not firing...need more info, what else have you done to car?
The car is completely stock with the exception of a bbk cold air intake, bbk headers and exhaust system(Mac x pipe and Mac exhaust) and lastly the short throw shifter. I bought the car that way back in October. I replaced the spark plugs, ignition wires, the distributer cap and rotor and the fuel filter back in November. Just put in a 3G 130amp alternator with the bigger power cable that runs from the alternator to the ignition system. But the problem was occurring before that. I just only noticed the misfiring and the idle bouncing when the headlight were on because the light made it more noticble. Although now it got worse obviously because it happens during the day. It seems the misfiring happens more when it's really cold. Because that problem happens on an off with the headlights off but more with them on.
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Old 01-27-2014, 04:41 PM   #5
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Check your charging system. Voltage regulator on the alternator, belt tensioner and belt condition.

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I replaced the alternator with a 3G 130amp one and also put a bigger power wire with it that connects to the alternator and runs to the ignition system. As for the belt and tensioner I guess they're something I could replace. It does look like it is running slow. How do I check and fix the timing? I've never dealt with timing before.
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Old 01-27-2014, 04:50 PM   #6
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Before replacing the belt and tensioner. Test it. Belt should a little bit of deflection when you push on it. I would say no more than 1 inch. Also, the tensioner should not look like its bouncing up and down easily. The belt should not be cracked, check the ribs of the belt. If that checks out then that's not the issue.

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Old 01-27-2014, 04:55 PM   #7
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Timing is checked with a timing gun. Or a really good ear. To adjust, loosen distributor hold down bolt slightly. Turn the distributor. As you turn iy , you will notice the idle going up or down depending on which way you turn it. Timing gun hooks up to the battery and clamped spark plug wire #1. Aimed at the crank with the timing indicator.

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Old 01-27-2014, 05:06 PM   #8
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Timing is checked with a timing gun. Or a really good ear. To adjust, loosen distributor hold down bolt slightly. Turn the distributor. As you turn iy , you will notice the idle going up or down depending on which way you turn it. Timing gun hooks up to the battery and clamped spark plug wire #1. Aimed at the crank with the timing indicator.

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Okay well I just want out at looked at the belt if I push down on it, it seems to only push down about 1/4 of an inch. It doesn't look cracked anywhere it looks like it's been replaced within a year. It's a belt from napa. It does have a tiny bit of brown color to it. But it's like a light brown probably just because it's been used. I turned the car on to let it run and the actual tensioner is fine. It's not bouncing. As for timing can I go to the ford dealership or a specific shop to get the timing checked? If so how much should it cost around? Sorry about all the questions. I've never messed with timing and this is my first mustang although I have worked on engines a bit.
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Old 01-27-2014, 06:36 PM   #9
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I couldn't see your attachment so I don't know where your idle is at but normally it should be around 700 to 1000 for a5.0. If your idle is surging between those numbers, your timing should be normal. Unless you've done work to the timing chain or if the timing went out of whack then you would have more issues than what you have. I would check air induction system. MAF sensor could be dirty. Or the idle air control valve could be stuck with carbon or faulty.

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Old 01-27-2014, 06:41 PM   #10
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I couldn't see your attachment so I don't know where your idle is at but normally it should be around 700 to 1000 for a5.0. If your idle is surging between those numbers, your timing should be normal. Unless you've done work to the timing chain or if the timing went out of whack then you would have more issues than what you have. I would check air induction system. MAF sensor could be dirty. Or the idle air control valve could be stuck with carbon or faulty.

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It's bouncing at 700rpms like fast going up and down but only about 1cm up and down. I don't believe I have the maf system I think it's still the older one. As for the iacv what can I clean the out with if I don't have carb cleaner? Is there anything I can use or is it worth it to just buy a can? Thanks a lot
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Old 01-27-2014, 07:00 PM   #11
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Brake fluid cleaner can be used too. When you remove the iacv, the pintle should move back and forth with little resistance. So the bbk air tube goes straight from the air filter to the throttle body with nothing in between?

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Old 01-27-2014, 07:10 PM   #12
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Brake fluid cleaner can be used too. When you remove the iacv, the pintle should move back and forth with little resistance. So the bbk air tube goes straight from the air filter to the throttle body with nothing in between?

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Okay. Now when removing the iacv I'm not gonna need a multimeter or anything of that nature when I install it correct?.. Also as for the bbk question I believe so. The actual chrome tube for the air duct doesn't contain a part of the tube with a sensor on it that would plug into a sensor on the engine.
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Old 01-27-2014, 07:18 PM   #13
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Not unless your check for voltage at the iacv. Simply remove it from the throttle body and look into with a flashlight. Check for carbon build up. Once complete reinstalled being careful not to over torque the bolts.

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Old 01-27-2014, 07:24 PM   #14
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Not unless your check for voltage at the iacv. Simply remove it from the throttle body and look into with a flashlight. Check for carbon build up. Once complete reinstalled being careful not to over torque the bolts.

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Okay. Should I not disconnect it from the sensor then? I don't currently have a multimeter because mine broke on me. What should I do to prevent the multimeter test?
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Old 01-27-2014, 07:27 PM   #15
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Yes you could disconnect the connector from the iacv. Make sure the key is off.

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Old 01-27-2014, 07:30 PM   #16
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Yes you could disconnect the connector from the iacv. Make sure the key is off.

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Okay, I'll do that so as long as the key is off and I don't over tighten the bolts it won't effect the reading?
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Old 01-27-2014, 07:34 PM   #17
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No. This check is only to see if there is carbon buildup in the Idle air control valve. If there is, just spray some cleaner in there, let it dry, and then reinstall it. Make sure you don't rip the gasket material.

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Old 01-27-2014, 07:36 PM   #18
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No. This check is only to see if there is carbon buildup in the Idle air control valve. If there is, just spray some cleaner in there, let it dry, and then reinstall it. Make sure you don't rip the gasket material.

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Alright thanks. I'll let you know what's going on tomorrow.
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Old 01-27-2014, 07:43 PM   #19
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Ok. Check your vacuum lines too for air leaks.

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Old 01-27-2014, 08:02 PM   #20
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Could still be a fuel pump going out. Double check your plugs and wires, could have crossed a plug wire. Make sure you're getting good airflow, then check for spark, lastly check for proper fuel flow.
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Old 01-28-2014, 07:02 AM   #21
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If voltage on tps is off or gone bad will cause idle issues
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Old 01-28-2014, 07:35 AM   #22
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Good call (Liebert91stang). Check the wires at the connector very carefully. I've seen copper wires break on the inside of the insulation with no outside visible signs.

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Old 01-28-2014, 08:24 AM   #23
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Good call (Liebert91stang). Check the wires at the connector very carefully. I've seen copper wires break on the inside of the insulation with no outside visible signs.

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So I bought carb cleaner and went to clean out the iacv and there's nothing clogged in it. It's literally almost new... There's pictures posted. I sprayed carb cleaner in it anyway and am going to reinstall once it drys. As for the tps I'll check the wires but what should the voltage be set at? When the car is off and the car is on? I'll have to snag a multimeter. Also I included a pic of my cai from bbk so that you could see what I mean by no maf sensor. I don't even believe my car was upgraded to maf.
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Old 01-28-2014, 08:31 AM   #24
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Could still be a fuel pump going out. Double check your plugs and wires, could have crossed a plug wire. Make sure you're getting good airflow, then check for spark, lastly check for proper fuel flow.
ignition wires arent crossed theyre correct. I have spark on all 8. How do i check fuel flow?
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Old 01-28-2014, 09:02 AM   #25
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Here's the deal. Since it is a fuel injected engine, not carburetor, the computer needs to know how much air is going into the engine so it can adjust how much fuel to put in. Without the air flow meter, MAF, the computer is pretty much guessing on how much fuel to put in. Which could be why you have a rough idle. From the looks of the photos you submitted, it is missing the MAF sensor.
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Old 01-28-2014, 09:06 AM   #26
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Here's the deal. Since it is a fuel injected engine, not carburetor, the computer needs to know how much air is going into the engine so it can adjust how much fuel to put in. Without the air flow meter, MAF, the computer is pretty much guessing on how much fuel to put in. Which could be why you have a rough idle. From the looks of the photos you submitted, it is missing the MAF sensor.
Oh okay. If it's fuel injected does it have to have the maf set up though? If so where would the connector be that plugs into the sensor?
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Old 01-28-2014, 09:14 AM   #27
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Yes, It does need it. I have the bbk cold air intake set up as well with the maf sensor connected. As far as where the connector is on your car, you're going have to look for it. It should be around the cold air intake tube. The previous owner might have hid it. I think its a four wire connector.

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Old 01-28-2014, 09:19 AM   #28
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Yes, It does need it. I have the bbk cold air intake set up as well with the maf sensor connected. As far as where the connector is on your car, you're going have to look for it. It should be around the cold air intake tube. The previous owner might have hid it. I think its a four wire connector.

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Do you have an 88 though? I'm looking up maf in the 5.0's and seems like only the 1989 versions and above had it. Bbk actually sells the cold air intake without a maf sensor designed for mustangs without one. I think 1986-1988 didn't have a maf meter.. Check it out. Link is below.


BBK Mustang V8 Fenderwell Cold Air Intake Kit (86-88) 1557K - LatemodelRestoration.com
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Old 01-28-2014, 09:40 AM   #29
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AutoTraderClassics.com - Article Curing Rough Idle

This link may be helpful. Check it out.
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Old 01-28-2014, 09:52 AM   #30
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AutoTraderClassics.com - Article Curing Rough Idle

This link may be helpful. Check it out.
Thanks for the link! I guess it's just time to start hunting. I definitely have the speed density system and not the maf system because I do have a map sensor. Well ill be having fun poking around! Thanks!
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Old 01-28-2014, 10:08 AM   #31
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No problem. Keep us updated.
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Old 01-28-2014, 10:13 AM   #32
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I will say this though, I would do some research into your 130 amp alternator. I say that because I had a Silverado come into the shop the other day with the same issue. Headlights were dimming and and appeared to misfire every now and then. The charging system voltage was erratic, jumping from 11 volts to 15. I replaced the alternator. Fixed the issue. Just food for thought.
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Old 01-28-2014, 10:24 AM   #33
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88 didn't have maf.it is speed density therefore you won't have mas.as far as checking fuel which shouldn't make idle off you should have a port off fuel rail that has schrader valve on it.correct way is fuel gauge but you could push valve in and see if fuel comes out.or pull spark plug and wipe it off then reinstall and try to start and pull plug to see if it has gas on it
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Old 01-30-2014, 10:47 PM   #34
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88 didn't have maf.it is speed density therefore you won't have mas.as far as checking fuel which shouldn't make idle off you should have a port off fuel rail that has schrader valve on it.correct way is fuel gauge but you could push valve in and see if fuel comes out.or pull spark plug and wipe it off then reinstall and try to start and pull plug to see if it has gas on it
Well I posted another thread just about misfiring and includes videos. I wish I could check the spark plugs but it's too cold at the moment. It's only 17degrees in jersey.
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Old 02-01-2014, 06:29 AM   #35
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Mine was doin the same thing after bout months and $500 later found out it was the three wires That plugs n to the o2

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