01' 3.8L V6 Mustang - Occassional High RPMs - Unsolved 1 year problem

FOXWYVERN

MEMBER
2001 FORD MUSTANG
3.8L
V6
RWD
AUTOMATIC
135,000 MILES

-Car Specifications
Make: Ford
Model: 2001 Mustang
Engine: 3.8L v6
Trans: Automatic

-Description
To start with, there is no engine light associated with this problem. This problem has been going on for more than a year now and I have had a mechanic look at it in the past. I was hoping the engine light would have come on or at least the problem to get worse to help identify the exact cause but I think time has run out for this option

The problem is most noticeable while the car is parked and idling. The engine RPMs are obviously to high and can occur both when you first start the car or after driving it for awhile. RPMs at its most extreme clocked in at 3,000RPMs while at idle although more recently it's more around 1,200RPMs to 1,500RPMs. The problem is sporadic and can suddenly go away as quickly as it starts. Sometimes I can go a month without it happening, sometimes it feels it's the whole month that it is happening. Temperature does not seem to be a factor as it has happened in the heat of summer and dead of winter both when the car is cold and hot. While in idle, you can sometimes catch the car stepping up and stepping down the RPMs by a factor of 100RPMs and the RPMs tend to fluctuate. Normally, while the RPMs are high, you'll also notice the RPMs drop slowly by 200 to 400RPMS and then suddenly kick back up landing anywhere from higher to lower than it was just at. This process will repeat with the occasional continued drop on each high kick till the RPMs are back under 1,000 and sometimes it never seems to stop and can end up being even higher.

The problem can also appear to happen while the car is in gear but it much harder to identify by watching the RPMs. Only when the problem is extreme does it feel like the car is being pushed and you are fighting it with the break. What's much more noticeable while the car is in gear is when your coming to a stop. Right before you come to a complete stop, you feel what feels like a clutch in a manual vehicle start to pull out which is immediately followed by the car being kicked forward. How hard the car is kicked forward depends on how high the RPMs want to go. I used to believe that my transmission was starting to go until the problem became worse and I noticed it is directly associated with the high RPMs.

As I've stated previously, I've had a mechanic look at this problem. About 8 months ago the problem reached a peak with the RPMs jumping to almost 3,000 and I started to worry about rear ending someone when the car unexpectedly kicks forward. The mechanic did a series of tests, cleaned the manifold, replaced the Idle Air Control Valve, and I believe replaced some sort of canister in the EVAC system although I can't find my receipt at the moment. When I got the car back, the problem was back to its occasional problem of 1,200-1,500 RPMs, and the mechanic sent the IAC back as defective, mentioning it had a short and installed a new one. The problem seemed to have go away but it didn't take long to show back up and I've been driving with it ever since hoping the engine light would come on.

-Symptom Summary
RPMs ocassionally to high during idle
RPMs ocassionally to high while in gear
Vehicle kicks forward when approaching a stop followed by high rpms

-Attempted Fixes
IAC replaced twice
Manifold cleaned
EVAC Canister replaced (I think)

-Other known problems
Exhaust leak near the exhaust manifold
Vampire drain from radio (Temp Solved: Pulled Fuse)
Overdue for new spark plugs and coil

Anyway, I'm going to use my tax return to try and resolve this issue before it causes something worse like ruining the transmission or something. I'm attempting to increase my knowledge on the issue as much as possible before I go into try and tackle this one again.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Tyr cleaning the throttle plate on both sides with choke cleaner and iac hole they get gummy and stick. Check for a vacuum leak like hoses off/cracked or holes in them cost of choke cleaner about $4 at autoparts.

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Sunday, February 16th, 2014 AT 4:45 PM

FOXWYVERN

MEMBER
3 POSTS

All this was done by the family trusted mechanic without success 8 months ago. This and the parts replaced helped but never completely solved the problem.

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Sunday, February 16th, 2014 AT 4:49 PM

CARADIODOC

MECHANIC
33,858 POSTS

The first suspect would be a vacuum leak. That will cause an increase in engine speed without a corresponding increase in power. The obvious vacuum hoses have probably been checked already but there could be a leaking intake manifold gasket or a worn bushing for the throttle blade in the throttle body. You can try spraying water on the engine while it's running and still cold to see if it gets sucked in somewhere. The next step is to use a smoke machine to inject a white, non-toxic smoke into a vacuum hose that sends the smoke into the intake manifold, then you watch where it sneaks out. If it comes out the oil fill hole when the cap is removed, suspect an intake manifold gasket.

You do not need the Check Engine light to turn on. In fact, for this problem it may not. There are well over a thousand potential diagnostic fault codes and only those related to something that could adversely affect emissions must turn the light on. High or erratic idle speed on its own won't affect emissions. If the CAUSE of that erratic idle could increase emissions, that will turn the light on and set the appropriate code. All mechanics know the place to start is by checking for codes, even when there's no Check Engine light.

The next step is to connect a scanner to view live data and see what the Engine Computer is seeing and responding to. As with almost everything else, Ford does this differently than all other manufacturers. Your idle air control solenoid will be shown in "percent" instead of "steps". What you want to look at is which way that is moving in relation to how the idle speed is changing. If the percent goes down when the engine speed goes up, the Engine Computer is trying to reduce speed without success. If the engine speed and idle air percent go up at the same time, the computer is doing that in response to something, and you have to look at what else is changing.

The idle air control solenoid is out of the picture when the throttle is off idle, so if you feel surging while you're driving at a steady speed, go back to looking for vacuum leaks.

Look for things that affect fuel metering like high or low fuel pressure, or erratic readings from the mass air flow sensor, map sensor, or throttle position sensor. If any of those readings aren't steady, start by checking their connectors for corrosion on the terminals or loose-fitting terminals. Wiggle those connectors a little to see if engine speed changes.

Also be aware an exhaust leak will cause fuel metering problems. Between the puffs of exhaust flow, the momentum creates little pulses of vacuum that can draw in outside air. The oxygen in that air gets detected by the oxygen sensor, and the computer only knows that side of the engine is running lean. It tries to make up for that by adding fuel to all the cylinders on that side of the engine. You'll see that on the scanner as very high positive fuel trim numbers. The problem is, no matter how much fuel it adds, there will always be that unburned oxygen sneaking through the leak, and the oxygen sensor will continue to detect it. The computer will keep on trying to add more fuel, and you'll smell that at the tail pipe, but it will continue to think the mixture is too lean.

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Sunday, February 16th, 2014 AT 5:15 PM

CJ MEDEVAC

MECHANIC
11,004 POSTS

WHILE SITTING IN THE YARD

. MIGHT TRY THINGS LIKE

----PLUGGING OFF THE BRAKE BOOSTER VACUUM LINE TO SEE IF THE IDLE SETTLES DOWN

IF IT DOES, MAYBE THE BOOSTER IS LEAKING INTERNALLY----THIS SAME TEST MIGHT BE DONE WITH OTHER ITEMS

. AND YOU DID TAKE OFF THE IAC AND CLEAN IT. REALLY? OR IS THIS AN ASSUMPTION?

'BOUT THE WORSE THING I'VE ENCOUNTERED WITH THIS VEHICLE IS THE PLUG WIRES FROLIC AND DANGLE ABOUT ALL OVER THE ENGINE COMPARTMENT. THEY TEND TO SCUFF HOLES IN 'EM FROM RUBBING METAL. THEN THE MISFIRING BEGINS!

WHEN YOU REPLACE 'EM, USE SHORT "SPLIT, OPEN" PIECES OF 3/8 FUEL OR VACUUM LINE OVER THE PLUG WIRE AT THE PROBLEM AREA TO KEEP 'EM FROM SCUFFING

KEEP US INFORMED

THE MEDIC

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Sunday, February 16th, 2014 AT 6:27 PM

FOXWYVERN

MEMBER
3 POSTS

Some very informational replies. Lots of knowledge here and very impressive. I didn't think I would find this kind of help on the Internet.

Good to know to go ahead and check for codes. The vehicle has had problems with computer resets due to the battery dieing constantly from the electrical vampire leak. Now that the fuse for the radio has been pulled it may have built up data to give a proper diagnostic. So I'll start there before I hand it over to the mechanic.

Additionally, regardless of what the codes show and point to. I'll be also focusing on the exhaust leak and I'll let the mechanic decide on what has to be done in regards to this.

My car tends to fill with fumes when at idle, especially in enclosed parking spaces like parking decks so this problem has been a growing priority to have taken care of. I've had a number of people tell me that the problem can't be related but after reading this I'm a little optimistic. I'll start with the exhaust simply given the fact that it was on the "To do" list.

My vacuum lines do show some weather to them but I've had the vacuum system checked in the past for this problem and the tests didn't show anything wrong with the exception of the EVAC canister which I assume is the one back near the gas tank on my vehicle.

As for the IAC, it has been cleaned, and replaced twice with brand new ones with no real solution other than the extreme idle of 8 months ago at 3,000RPMs.

All the rest of the information is highly valuable and I am thankful for you guys taking the time to share them. I will do my best to keep you all informed as I continue to tackle this problem.