Seafoamed car and drastic mpg improvement, but idle is bad

MustangLife · Sep 18, 2011

Hey all. Ran seafoam in my 03 gt the other day. 1/2 can in oil, 1/2 can in vacuum and 1 whole can in gas tank. Blew white smoke 80 feet in the air it seemed it was crazy. But after 400 miles I have a funny idle. For example and its in a pattern too.....

Car is idling at 900rpms (which is normal for my car) idles for about 6-7 seconds and than drops to 500-600 rpms like its gonna stall for about 2 seconds and than the same pattern again over and over.

The car runs great and definately seafoam is the way to go. I got 105 miles on the highway on 1.4 tank of gas running 80 or so mph at 2700,2800 rpms with my 4.10's.

I ran the seafoam through the vacuum hose that goes to the iac valve. Did I trash the IAC valve? Or does it just need a cleaning itself. I figured the seafoam would have cleaned the iac not make it act up.

The idle problem only started after I seafoamed the vacuum line to IAC.

Thanks in advance
Josh

bdcardinal · Sep 18, 2011

Take the IAC off and clean it out. Also pull a plug and check it. A lot of times the seafoam thing fouls out the plugs.

wmburns · Sep 18, 2011

Have you recently disconnected the battery?

Just wondering if the AC is short cycling? Is the change in idle speed related to the AC compressor engaging/disengaging?

How old is the PCV valve?

MustangLife · Sep 18, 2011

PCV is the original one. Battery hasn't been disconnected in a few months. The idle problem is with the a/c on or off. Not relative to the AC compressor engaging/disengaging? I pulled the IAC off and had a little gunk in it but not to bad. But i cleaned it as best I could with rubbing alcohol and q-tips. No electrical parts cleaner or anything like that so I used alcohol. But the idle is still the same now. The car is not missing or anything. The plugs are perfect, don't need to be replaced. The car is running as good as it ever has. FYI no check engine light either.

Stays at 900 for 7 seconds and drops to 500-600 for a second or 2 and than back up to 900 for 7 seconds. Over and over.

GDawg · Sep 18, 2011

Sounds like a vacuum leak to me. Check the connections you touched and all the vacuum connections close that you could have pulled loose.

Not sure you are supposed to clean your IAC that way but concentrate on the vacuum leaks.

wmburns · Sep 18, 2011

Find out what's changing, at the low point, and you will be 3/4 the way there.

IMO, focus on one possibilities such as:

bad PCV value. PCV value is sticking and allowing too much air, the IAC attempts to correct (bring the idle down). PVC value frees up and now there's too little air. Process repeats. IMO, as cheap as a PCV valve is and considering it's original, it's plain silly (read stupid) to not replace it. Remember, the PCV value is basically a controlled vacuum leak. So check the PCV breather lines, grommet, oil dip stick, oil cap, and valve cover gaskets as well.

Vacuum leak. Focus down stream of the TB

The IAC value is sticking internally. This is causing it to hunt for the correct idle. This diagnosis can be confirmed by monitoring the IAC duty percent as the RPM's are changing.

The throttle body linkage is loose or worn. This is allowing the TB to loosen as the vacuum falls. This lets more air in and the cycle repeats.

Other possible causes could be the TPS. This can be confirmed by monitoring the TP-MODE PID to see if it switches from "P/T" to "C/T" as the RPM's change.

Check out the following for more information on how to trouble shoot IAC and idle issues.

Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums

trinity_gt · Sep 18, 2011

MustangLife said:
I ran the seafoam through the vacuum hose that goes to the iac valve. Did I trash the IAC valve?

Wait...you mean you fed the SF into the big fat fresh air line leading to the IAC?

If so, this is probably not a good thing. The IAC is intended to regulate the flow of air, not liquid. It may not be sealed well enough to keep the solvent out of the inner workings.

The solvent may vaporize over time on its own. I doubt you'll see much if you take the thing off. Just leave it be for a while and see if the idle improves over time as the solvent has a chance to boil away due to engine heat...

MustangLife · Sep 19, 2011

trinity_gt said:
Wait...you mean you fed the SF into the big fat fresh air line leading to the IAC?

If so, this is probably not a good thing. The IAC is intended to regulate the flow of air, not liquid. It may not be sealed well enough to keep the solvent out of the inner workings.

The solvent may vaporize over time on its own. I doubt you'll see much if you take the thing off. Just leave it be for a while and see if the idle improves over time as the solvent has a chance to boil away due to engine heat...

Yes I did. Guess we all make mistakes sometimes. Basically you're saying drive it around for a week or two and see if the idle goes back to normal. Than replace IAC.

MustangLife · Sep 19, 2011

Thanks for all the help everyone. I'm gonna look into it. There is no vacuum leak. I've checked everything and reinstalled. I'm gonna unhook the battery for 30 min and let the car re-learn everything and see how it goes. I'm leaning more to the IAC valve is the issue like trinity gt said. Anybody know how much the IAC runs at the dealer or advance and what brand to get or stay away from

sn95jones · Sep 19, 2011

I seafoamed my car a couple months ago, blew out very little to no smoke at all, when I pulled the heads off, I realized why no smoke was coming out, the damn motor was spotless! No carbon buildup at all. I was baffled for a 96' GT it had no carbon buildup

trinity_gt · Sep 19, 2011

sn95jones said:
I seafoamed my car a couple months ago, blew out very little to no smoke at all, when I pulled the heads off, I realized why no smoke was coming out, the damn motor was spotless! No carbon buildup at all. I was baffled for a 96' GT it had no carbon buildup

Modern cars use feedback control for fuel delivery so fuel metering is very precise and thus there's little carbon accumulation.

Carbon will accumulate in places it shouldn't if oil is getting past the rings or valve seals or is being inhaled through the PCV system. Rings can become fouled if the oil is neglected (i.e. not changed often enough to suit the driving conditions).

But really, modern engines run so cleanly I wonder about the sense of using stuff like SF in them. And if the car is carboning the backs of intake valves or exhaust ports or piston crowns it's probably got mechanical issues that need addressing...

Deleted member 38176 · Sep 19, 2011

MustangLife said:
Yes I did. Guess we all make mistakes sometimes. Basically you're saying drive it around for a week or two and see if the idle goes back to normal. Than replace IAC.

You almost had the correct hose lol. Everyone makes mistakes and you didn't seriously harm the motor/intake. For future reference, this is the valve you want to use for seafoam.....

MarkF · Sep 20, 2011

Nightfire said:
You almost had the correct hose lol. Everyone makes mistakes and you didn't seriously harm the motor/intake. For future reference, this is the valve you want to use for seafoam.....

For future reference, in your picture would I put the seafoam into the hose leading away from from the TB or into the metal port going into the TB?

trinity_gt · Sep 20, 2011

MarkF said:
For future reference, in your picture would I put the seafoam into the hose leading away from from the TB or into the metal port going into the TB?

The metal bit going into the plenum.

The hose runs to the PCV valve which plugs into the valve cover and isn't a source of vacuum.

If I'm not mistaken, on the rear of the plenum is a smaller, more convenient vacuum port used for the HVAC controls. I'd probably use that because (a) it's easier to find a hose to fit it and (b) the smaller diameter will prevent the engine from sucking great quantities of the stuff all at once.

Deleted member 38176 · Sep 21, 2011

MarkF said:
For future reference, in your picture would I put the seafoam into the hose leading away from from the TB or into the metal port going into the TB?

As trinity mentioned, the metal inlet flowing INTO the plenum. An easy way of doing it is to go to a hardware store like Lowes or Home Depot and buy a short piece of their clear plastic tubing that fits snugly onto the metal tube. It makes it MUCH easier to get the seafoam into the motor

Stumbaugh · Sep 21, 2011

I Seafoamed mine yesterday. I figured after 161k miles, it could probably need it, and it definitely did. It runs more smooth now and idles alot more smooth. It had a very heavy smoke for over 5 minutes. I then took it on a 80 mile round trip, all of which it still had a light smoke to it. It finally stopped right before I got home. I would say it needed it.

Deleted member 38176 · Sep 22, 2011

Stumbaugh said:
I Seafoamed mine yesterday. I figured after 161k miles, it could probably need it, and it definitely did. It runs more smooth now and idles alot more smooth. It had a very heavy smoke for over 5 minutes. I then took it on a 80 mile round trip, all of which it still had a light smoke to it. It finally stopped right before I got home. I would say it needed it.

You have an 02 with 161K? Damn that car has seen a lot of road. I've only got 70K and I thought I drove mine a lot lol

Stumbaugh · Sep 22, 2011

Yep and I spray the **** out of it every chance I get. Still runs like a champ

40oz · Sep 23, 2011

Stumbaugh said:
I Seafoamed mine yesterday. I figured after 161k miles, it could probably need it, and it definitely did. It runs more smooth now and idles alot more smooth. It had a very heavy smoke for over 5 minutes. I then took it on a 80 mile round trip, all of which it still had a light smoke to it. It finally stopped right before I got home. I would say it needed it.

Anyone ever done a before/after dyno test? LOL

Seafoamed car and drastic mpg improvement, but idle is bad

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