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Discussion Starter · #1 ·
This started when I got the car back from the mechanic after they replaced the coil pack and coil wire (about 11 months ago); when I let off of the gas the RPM drops and the battery light comes on, most of the time it doesn't die, but occasionally it does. It has also developed a habit of becoming difficult to start, sometimes having very low RPM at idle after initial start up and sometimes having very high idle at start up. I went to Autozone and had them check the engine codes (had a CEL for a day or so) and they said it indicated the TPS; I replaced that and the problem persists.

I've read through a lot of threads on here, and I see that there are a whole lot of very knowledgeable individuals here, so I'm hopeful that someone can point me in the right direction. Any help is greatly appreciated. Thanks a lot in advance!
 

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Why did you initially replace the coil pack and wires? Was it age or did you upgrade the ignition system for better performance?

Have you done any other mods to the car?

My first thought is a dirty MAF sensor, sending faulty values to the ECU for the fuel/air ratio. Then comes vacuum leaks or DPFE sensor gummed up.

Need a little more background info on the car for better diagnosis...
 

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Discussion Starter · #3 ·
Thanks for the reply. The coil was replaced because the car was running poorly, misfiring (seemed to be a timing issue).

There are no mods to the car that I'm aware of. I have checked for vacuum leaks crudely, by spraying flammable brake cleaner near particular areas of the engine compartment (near vacuum lines) to try and find a leak, no luck.

If it helps, it's a stick shift (are there even automatic SVT?) 3 door (hatch)with around 108,000 miles on it.
 

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Usually the engine dying coming off RPMs to idle is the Inlet air control valve.

that valve is really a P.I.T.A. in my opinion.
It works great, but when it fails or starts to fail it really is bad.
And any time I ever had a mech try to 'clean' it, it invariably fails within a few weeks/ months.

So that is my suggestion. replace the IAC valve.
Anytime it is an engine dies off as the RPM drops (freely)..... that is the IAC.
Idle stuff may also be other stuff. But the dies off RPM. is the IAC.
 

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Check you grounding to the battery (positive and negative cables). If you car almost dies and the battery light comes on that might be your problem for sure.
If you press the throttle more it wont die right?
 

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you dun stole my comment^

but yes check that. also check the connection at the alternator, engine ground cable, battery to ground cable and the battery terminal connections and wires. and inspect wires for frays/possible shorts. and make sure alternator is tight(alternator grounds to engine, engine grounds to car) also check for corrosion at all of those places(and under coil pack) if everything checks out ok, have your battery and alterntor tested. and check the belt as well. make sure it has proper tension.

if all thats good(battery light may be coming on because engine RPM too low) check and clean MAF sensor, check throttle position sensor, and idle air controler.

so many options!!!!!(cars kinda suck like that, yet we all love them)i wish you luck in finding the solution.
 

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I didn't know that the SVT had a coil wire............
 

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I always recommend cleaning and re-installing the IAC first. It's about a $50 part, and tends to collect black crud from the oil breather. Over time it fails to work like it should. It's only a solenoid operated valve, so just clean it with anything- carb cleaner, etc. You'll need Q-tips to clean off the shaft. Make sure the seal around the plunger head is not damaged.

If you have platinum plugs, don't be surprised if you don't see much in the way of spark plug deposits, but always check gap, and look for damage.
 

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I am not exactly sure where the IAC is because I have a zetec but it has to be on the intake manifold, most likely under runners like it is on my zetec and was on the spi. Also what about the IMRC, could that cause the idle issue?
 
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