Vacuum Leak I think!?!? Or Failed Valve?

Yes It could be Idle Air Contol...but before i start a step by step for you to replace it, I want pics of spark plugs, the IAC is about $55-$60 and a PITA to replace with the motor in...

Go pull the COP covers from over the valve covers. Start the car, one at a time pull the COP off the spark plug...if it is a WORKING cop the engine will start mis-firing...you'll know immediatly that because you've unplugged a working item, the engine isn't happy about it...IF you pull one and there is no change in idle, that tells you that there is no signal or spark in that cylinder...easy step first, just flip flop that cop with an adjacent one and retry same procedure...
Then if the flip flop moves...you've got a bad coil..if no change was made in idle with a swap..check plug..if plugs look ok and are gapped properly at .054 then you will need a Noid Light to check for pulse, no other light flashes fast enough...
I hope that at least one of our options helps you man, good luck...
And don't mind Bill, he means well, just grumpy cuz I have his pez dispenser
 
Ugh. The IAC is less then a 5 minute fix on his car. Its not stupid like the first gens. Der.

And pulling coils to find the problem is not a great idea. You pull a working coil and the ECU sees a fault. It may ignore it but then you go unplug another working coil and it sees another fault. At this point the engine can go into safe or limp mode and may start ignoring a sensor that could also very likly be an issue.

If its not the IAC and you cant find a vac leak and the plugs are not fouled AND there is no CEL then the next step is to find a shop that has a proper scan tool and have them scan the coils, IAC DC, TPS, MAF etc etc

Hell my 98 had a fine idle and ran great and seemed to have power but was breaking up on the upper RPMs. The shop hooked a scanner to it, found two weak coils and an injector not completing its DC.
I would have NEVER found that without the scan tool.
 
Before you drop the money on the IAC, you should buy a can of Throttlebody cleaner and clean it out, as well as a can of MAF cleaner (Mass Air Flow). Nine times out of ten, the problem is usually something simple.
 
The plot thickens.. and I think LaserSVT might be on to something...

I realized today, my car only idles like this while the brake is on, when I put it in park... smooth sailing (well.. occassionally a slight rumble, but I only notice cause Im looking for it). Does this help clarify anything??

Weather in park, or with brake, my RPM's stay the same, but the engine SOUNDS like its under less strain...??
 
97MarkVIIILSC said:
My car idles one notch below 1k, it sometimes hangs when I let off the gas, but nothing crazy. I dont think its the problem. I do think my right front brake pad is sticking, since my car pulls to the right upon braking, and that might be affecting my mileage, but in regards to the decrease I was comparing my normal driving stlye each day and also noting the sudden decrease while conditions remained the same.
Click to expand...

Check The Outter Tie Rod end, if its pulling you may also have a worn end... does it cause the wheel to wobble when braking?
 
Sapperfire said:
Yes It could be Idle Air Contol...but before i start a step by step for you to replace it, I want pics of spark plugs, the IAC is about $55-$60 and a PITA to replace with the motor in...

Go pull the COP covers from over the valve covers. Start the car, one at a time pull the COP off the spark plug...if it is a WORKING cop the engine will start mis-firing...you'll know immediatly that because you've unplugged a working item, the engine isn't happy about it...IF you pull one and there is no change in idle, that tells you that there is no signal or spark in that cylinder...easy step first, just flip flop that cop with an adjacent one and retry same procedure...
Then if the flip flop moves...you've got a bad coil..if no change was made in idle with a swap..check plug..if plugs look ok and are gapped properly at .054 then you will need a Noid Light to check for pulse, no other light flashes fast enough...
I hope that at least one of our options helps you man, good luck...
And don't mind Bill, he means well, just grumpy cuz I have his pez dispenser
Click to expand...

May be a bit late on the draw but the IAC on a 97-98 is real easy to get to... its the 93-96 Marks that were in the back by the TB/Firewall. :)
 
96_Lincoln_LSC said:
Check The Outter Tie Rod end, if its pulling you may also have a worn end... does it cause the wheel to wobble when braking?
Click to expand...

The car wobbles at 65+, and I need to redo the front end I am sure!!! The sway end links are new, although cheap aftermarket replacements since I needed in a Jiffy. Might be the problem, but I am seeing excess brake dust on that wheel, so I think i found the culprit
 
97MarkVIIILSC said:
The plot thickens.. and I think LaserSVT might be on to something...

I realized today, my car only idles like this while the brake is on, when I put it in park... smooth sailing (well.. occassionally a slight rumble, but I only notice cause Im looking for it). Does this help clarify anything??

Weather in park, or with brake, my RPM's stay the same, but the engine SOUNDS like its under less strain...??
Click to expand...

when the brake is being depressed. its pulling vacumm from the intake manifold, if its going bad or leaking or there is another leak in the vacumm system you will notice a drop or surge in the RPM..
 
96_Lincoln_LSC said:
when the brake is being depressed. its pulling vacumm from the intake manifold, if its going bad or leaking or there is another leak in the vacumm system you will notice a drop or surge in the RPM..
Click to expand...

This is what I was thinking.. so I guess Im back to checking the intake gasket LOL..
 
97MarkVIIILSC said:
This is what I was thinking.. so I guess Im back to checking the intake gasket LOL..
Click to expand...

I'm going to laugh if you don't take my advice and end up spending thousands like I did! BUY THE FREAKING $3 CAN OF CARB CLEANER AND CHECK YOUR INTAKE GASKET! WORST CASE SCENARIO IS YOU WILL FIND OUT YOUR INTAKE GASKET ISN'T LEAKING AND YOU CAN ELIMINATE THAT DEFINITIVELY!
 
LaserSVT said:
Its not a game Sparky. I have been trying to help you and have given you good advice. I am also trying to save you a wild goose chase and looking for chit that ain't there.
Click to expand...

man the more this thread goes on i agree with laser it seems like your chasing a ghost.

the idle will be lower in gear vs park and engine will be under load in gear cuz its in gear...

millage will drop when sitting cuz your not moving

anymore on here it seems people are in a hurry to throw every part they can think of at their car. start simple. do a tune up (and dont use fukkin bosch plugs) check your boots and coils. if it still misses come back and we will reevaluate the situation. mine has a tiny shake to it at idle too, always has, ive just summed it up to thats how they run its not enough to see or for anyone else to notice but i can
 
Could you clarify something.. It only seems to bog or miss when you press the brake??

Your pull while braking could be either a bad hose, or binding caliper/ caliper guide pins
 
Ripped
Whats with the caps???
No coffee this morning?
Start with the simple stuff first, its trouble shooting 101.
Laser could be right it very well could be the IAC.
Or it could be a COP like sapp was saying or a bad plug.
Or it could be a vacuum leak on the tree.

These cars are know for all those issues.

Intake gasket is not a common problem.



If you own a Mark... your going to put more money into it then its worth.
The only way its worth it.... is if you can save the labor.
You not the only one who has thousands into a car that's a turd.
 
ive also seen brake boosters leak, the check valve on the line to the booster go bad. hell i can open the hood and just randomly point to shyt that could be your problem.
one more question is the ac on? try shutting that off, mine is slightly out of balance or something cuz she will shake a lil more with that on
 
It could be the alternator.
Maybe the tires are under inflated.

I heard that affects gas mileage. :shifty:

My car has a miss....I never notice it because its floored.

:burnout:
 
chicken said:
ive also seen brake boosters leak, the check valve on the line to the booster go bad. hell i can open the hood and just randomly point to shyt that could be your problem.
one more question is the ac on? try shutting that off, mine is slightly out of balance or something cuz she will shake a lil more with that on
Click to expand...

Brake booster is why I asked him to clarify the issue
 
Sapperfire said:
Could you clarify something.. It only seems to bog or miss when you press the brake??

Your pull while braking could be either a bad hose, or binding caliper/ caliper guide pins
Click to expand...

Its more jsut when Im sitting with the brake on... its very slight, I have to listen/look for it
 
If you've got a vacuum leak causing a rough idle, and you press the brake and the idle gets worse, then let off the brake and it goes back ....that would be a possible vac leak in the booster
 
Sapperfire said:
If you've got a vacuum leak causing a rough idle, and you press the brake and the idle gets worse, then let off the brake and it goes back ....that would be a possible vac leak in the booster
Click to expand...

I am going to do a tune up, since I have the plugs and everything - Ill check the COPS and see how they are while I do that. Ill also clean the MAF and intake, along with check it for leaks. I am going to toss on a buddy's IAC to see if it makes a difference.

Now, with all that done, if I am STILL feeling something odd, how do I check the Booster to see if theres a leak?
 
97MarkVIIILSC said:
The plot thickens.. and I think LaserSVT might be on to something...

I realized today, my car only idles like this while the brake is on, when I put it in park... smooth sailing (well.. occassionally a slight rumble, but I only notice cause Im looking for it). Does this help clarify anything??

Weather in park, or with brake, my RPM's stay the same, but the engine SOUNDS like its under less strain...??
Click to expand...
That actually throws my thought out the window. :lol:

If it gets worse with the brake on then its more then likely a vac leak. Could be a bad seal aroud the check valve going into the booster, could be cracked lines on the T fitting off the plenum or could be a bad brake booster.

Take some pictures of the line going from the booster to the T fiting and some pics of the T fitting and post them. If there is a problem we should be able to see it.


Really yo0u can too. Just look for ANY cracks in the line. If you see any or if you touch the vac line and your fingers are black then you need new ones. Also have someone press the brake pedal and stick your ear by the booster and see if it hisses.
 
LaserSVT said:
That actually throws my thought out the window. :lol:

If it gets worse with the brake on then its more then likely a vac leak. Could be a bad seal aroud the check valve going into the booster, could be cracked lines on the T fitting off the plenum or could be a bad brake booster.

Take some pictures of the line going from the booster to the T fiting and some pics of the T fitting and post them. If there is a problem we should be able to see it.


Really yo0u can too. Just look for ANY cracks in the line. If you see any or if you touch the vac line and your fingers are black then you need new ones. Also have someone press the brake pedal and stick your ear by the booster and see if it hisses.
Click to expand...



Ok will do all this when I leave today - but umm... WTF does the Booster look like?!? :D
 
Its the big black round thing ....(buncha peervs) on the drivers side o the firewall. Has the brake master bolted to it (thing that you put brake fluid in) and a big vac line going to it. It will his when the pedal is pressed but if the pedal is held still and it hisses then the diaphram is bad and thats where its leaking vac from.

You will need to go to a mechanic for that. Its an involved job and not to be a dick but if you dont know what it is then I wouldnt even try to swap it. A lot of stuff has to be moved to get to it.
 
LaserSVT said:
Its the big black round thing ....(buncha peervs) on the drivers side o the firewall. Has the brake master bolted to it (thing that you put brake fluid in) and a big vac line going to it. It will his when the pedal is pressed but if the pedal is held still and it hisses then the diaphram is bad and thats where its leaking vac from.

You will need to go to a mechanic for that. Its an involved job and not to be a dick but if you dont know what it is then I wouldnt even try to swap it. A lot of stuff has to be moved to get to it.
Click to expand...

Big Black thing... got it!!! Just the decription alone tells me itll be a problem to deal with!!! :)

Lets hope its not that, and just some faulty hose - the t fitting didnt look dry or rotted, but did look like it had a seam (or maybe a crack now that I think of it) I will check that too!

Thanks for all you guys help!!
 
Here is the booster circled in red.



1-14.jpg
 
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