1987 Mustang GT 5.0: Huge Help Needed

[Johnson’s GT]

To start this off I will be posting to many, many forums my problem. First off,

Details Of Motor:

Block: 302 bored 30 over
Crank: Stock
Pistons: Stock
Cam: B-303
Heads: Aluminum Gt-40 SVO
Rockers: Stock
Intake Lower: Gt-40
Intake Upper: Gt-40
EGR Spacer: 70mm
Throttle Body: 70mm
Intake Tube: Aftermarket Cold Air
Mass Air Meter Housing: 70mm
Headers: BBK Shorty 3/4
Cats: None
Exhaust Pipe: Off-Road H-Pipe
Mufflers: Flowmaster
End Tips: Dumps
Computer: ’93 A9L Mass Air Computer
Fuel: Stock Fuel Pump
Injectors: Stock 19lb
Fuel Lines and Tank: Stock

Problem(s):

First two problems interchange but first problem is more present:

1) Surging Idle ( 1500 rpms to shut off ):

When cruising at rpms higher then 1500, letting of the gas and pushing the clucth, the car’s idle will drop till it cuts off.

If cruising at the same rpm as above then slowing the car down to where it should it, then 50% of the time, it will stay there or it may surge till it cuts off.

If at idle the car will idle if cold but after a few minutes the car will start to surge till it cuts off.


Parts Tested To Find Problem:

Throttle Postion Sensor: Set to .97 Volts

Parts Tested But Not Sure If Bad:

Stock Mass Air Sensor: 12 Volts to + and - Wire, 12 volts to 3rd wire,
Signal Wire is the problem wire. It is suppose to stay at around the same idle at idle. It changes erratically at idle and when the throttle is pushed. Please give opinion.

Vaccum Lines:

All visible vaccum lines have been checked with cleaner to check for vaccum leaks. Advise if all lines should just be replaced.


Parts Replaced To Fix Problem:

Idle Air Control

2) Hanging Idle:

When starting the vehicle it will hang to around 2000 rpms then drop slowly to 1100 rpms.

As I push the throttle to gain speed then shift, it stays at that rpm for 2 to 3 seconds then drops to around 1100 rpms.

Parts Tested To Find Problem:

Throttle Postion Sensor: Set to .97 Volts

Parts Tested But Not Sure If Bad:

Stock Mass Air Sensor: 12 Volts to + and - Wire, 12 volts to 3rd wire,
Signal Wire is the problem wire. It is suppose to stay at around the same idle at idle. It changes erratically at idle and when the throttle is pushed. Please give opinion.

Vaccum Lines:

All visible vaccum lines have been checked with cleaner to check for vaccum leaks. Advise if all lines should just be replaced.

Parts Replaced To Fix Problem:

Idle Air Control

3) Whining/Whistle Noise:

Vehicle as a whining/whistle noise coming from the engine compartment at idle and cruise. Noise does increase as rpms increase. All gaskets and suppected hoses have been sprayed for leaks.

Parts Tested To Find Problem:

Vaccum Lines/Gaskets

Parts Tested But Not Sure If Bad:

Vaccum Lines:

All visible vaccum lines have been checked with cleaner to check for vaccum leaks. Advise if all lines should just be replaced.

Not the Problem:

Pulleys

My Note:

Please post on the thread or send me an email at [email protected]. I need help with this problem really bad. This is my daily driver and I have no clue what else to do. I need you to list what you think I should replace, test, or do to find the answer to my problem(s). Thank you so much everyone.

 

[Febreezeit50]

Doesn't sound like you pulled the codes?.

That would be where I start.

Jrichker will post soon with a self test method if you don't want to purchase a 20 dollar reader... good luck.

 

[7991LXnSHO]

There is a long, helpful post / checklist for this. Under search, type "surging idle checklist". Or you can find it toward the bottom of the list of sticky, easy to find conversations at the top of the 5.0 forum page. Write back after following the steps and let us know how it runs then. I hope it is great!

 

[7991LXnSHO]

Here are some ideas to check on the whining,/whistle noise. First do you have a mechanic's stethoscope? Harbor Freight has them for cheap and they are safer than a long screwdriver with the handle to your ear. Touch the other end to the possible noise maker, but not a moving part of it! Either tool works.
Parts to check.
MSD had an older style of coil that sang. Something about how the coils were wrapped or got loose made it noisy. The new ones do not sing. Mine was out of warranty, but worth the money to ditch the high pitch noise!

How about a bad bearing in the alternator (or other accessory)? These often accompany the end of the line for the alternator or air pump and are easy to pinpoint with the screwdriver listening technique. or undo the belt and spin each accessory by hand.

Is any stereo equipment on when you hear the noise? Ignition/alternator interference is annoying too.
Is the 70 mm throttle body a BBK? There is a post on them producing noise and how to fix it. But I think it is just at idle and full throttle.

 

[Johnson’s GT]

To Febreezeit50:

Codes are good. Checked myself. Sorry I didn’t include that.

To 7991LXnSHO:

I will try my mechanic’s stethoscope but I do not think it’s an accessory. I do not own a MSD Coil and the TB is not BBK. Thank you for the heads up on those products though. I will check the checklist. The noise also just sings the same tune when cruising but lowers in tune when back to idle.

See if that makes you think of something else.

 

[ID89GT]

Id check the throttle body.. bbk wasnt the only one that whistled

 

[Johnson’s GT]

To ID89GT:

TB is almost 7 months old and it has been whistling for about a week or so.

Thanks though.

 

[txstang84]

You mentioned a stock MAF, but in your description you say 70mm...are you running a 94-95 MAF? If your MAF voltage is all over the place when steady rpm above idle commanded, perhaps you have a dirty/faulty MAF. Idle voltages will move around a little with a cammed engine though...now, all that being said; have you tried re-clocking your MAF? I know it sounds trivial, and it may've been a coincidence, but I saw the idle on a buddy's car clean up significantly just by rotating the body of the MAF from one clock position to another. Check out the surging idle checklist sticky from jrichker...step by step procedures for cleaning up idle issues.

You also mentioned you checked all visible vacuum lines-what about the ones under the intake? The PCV hose? PCV grommet? Did you look at the vacuum tree for a crack? (I've seen this wreak havoc with SD/MA cars alike...usually SD worse) Whats the vacuum reading at idle? With a B cam, and factory timing set, it should probably be about 12-14" Hg. If it's less than that, look again for leaks. If you have any hoses that are heat formed, or rubber comes off on your fingers, just replace them-emission/vacuum hoses are cheap insurance.

Whistle or whine...if you've already eliminated the TB as the culprit, I'm +1 for the mechanics stethoscope...

 

[Johnson’s GT]

I just found out last night that the voltage meter was bad. Mass air checks fine. I just bought a mechanics scope from parts store. I will check it tomorrow. I also bought an upper intake gasket because I am going to replace vacuum lines and the upper intake needs to come off. So takes car of that. Will keep you updated.

 

[Blown88GT]

You mentioned a stock MAF, but in your description you say 70mm...are you running a 94-95 MAF? If your MAF voltage is all over the place when steady rpm above idle commanded, perhaps you have a dirty/faulty MAF. Idle voltages will move around a little with a cammed engine though...now, all that being said; have you tried re-clocking your MAF? I know it sounds trivial, and it may've been a coincidence, but I saw the idle on a buddy's car clean up significantly just by rotating the body of the MAF from one clock position to another. Check out the surging idle checklist sticky from jrichker...step by step procedures for cleaning up idle issues...

Did it myself, today, after tech help from C&L Performance. Sensor needs 6in of straight pipe in front of it; placing on outside of pipe curve eliminated hunting idle. However, std calibration tube is not optimal so am awaiting new tube.

 

[txstang84]

Ah-yes-that will definitely give you some grief. I used a 73mm C&L when I was still N/A after my EFI conversion...thing worked great on my car-even with a cheap-o eBay cold air kit. People wanted more for a nastied up factory airbox than for one of those cheap ones...and I didn't have a day's trouble with it.

 

[txstang84]

I just found out last night that the voltage meter was bad. Mass air checks fine. I just bought a mechanics scope from parts store. I will check it tomorrow. I also bought an upper intake gasket because I am going to replace vacuum lines and the upper intake needs to come off. So takes car of that. Will keep you updated.

Sounds good dude-good luck...

 

[VibrantRedGT]

Sounds like the Throttle Body blade. It can cause a whistle and can lead to surging idle. I think it was BBK that had whistling TB's back in the day.

 

[jrichker]

See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[94stangfan]

I agree check the checklist. I had a similar problem that was the ignition control module (grey box on the distributor) and cleaning of throttle body. Yeah, it didn't look dirty, but apparently it was.