98 LX P0505, IAC, rough idle, loss of power, #4 fouled, wtf

[Pro]

Ok, bought the car a few weeks ago. 98 LX 90K 5spd stock.

Ran like a friggin top 360 miles home, 38mpg averaging 70-80 mph

I decided to power wash the engine bay the next day.

I was pretty aggressive with the engine degreaser and the hose.


I ran it ~12 miles immediately after washing it to make sure it got nice and warm. Parked for an hour or two, then drove another 6-8 miles.

Parked it for about 8 hours and then got back in it. Within a mile it was running like crap. Felt like it was missing like crazy, flashing CEL, big power loss at more than 25% throttle. The car idled fine at that point, low rpms though ~400 on the tach, but smooth as butter.

Change the plugs and the car ran really well.....for about 20 miles.

Then the CEL came back and the same power loss.

Reset the ECU, cleaned the MAF, cleaned the TB, checked vac lines, seafoam in the gas, oil, and intake and replaced the cap and wire wheeled the rotor. Checked the new plugs and they still looked good. The idle adjusted itself after all this back to ~900. Car ran SUPER good......for about 20 miles.

Then the CEL came back and the same power loss.

Reset the ECU, pulled the IAC out. (Which by the way is very easy to take off and clean and there are NOT a lot of little parts in there that will fly all over.) I cleaned the valve and then reinstalled. I also pulled the plugs at that point and the #4 was fouled somethin fierce. The others looked OK.

The car instantly ran worse than ever. MAJOR power loss, instant blinking CEL, very rough idle (which was never an issue before) and at one point while turning the car around the engine held 3000 rpm almost as if the throttle was stuck open.

now it's pretty much un drivable. The 2 times I checked the DTC it was the same P0505.

The wiring harness and vac lines look beautiful, the intake pipe looks fine, there are no obvious defects on this car.

Where do I do from here?

Sourcing a used IAC is looking to be a little bit of a bitch. They are not the same as 95-96....new ones are at a min $200. Even if I do get one that doesn't mean it'll fix the problem.


I'm going to try and change the plug wires next, that #4 wire never felt like it was on very snug anyway.


any suggestions and guidance is appreciated.


if anybody has an IAC or even an whole TB assembly for sale let me know.

thanks

[MazdaNoob]

i would change the wires before you do anything else ..

[Squeekster1]

When i power washed my engine bay this summer, i had the same extremely rough idle and extreme loss of power. All that had happened was i got water in the plug holes. I took the plugs out and let it bask in the sunlight for a while to make sure any water that had gotten in the cylinders evaporated. Then I installed a new set of spark plugs and problem was fixed.


I got lost in your description of what you did so thats all the help i can give you.

[Pro]

I got lost in your description of what you did so thats all the help i can give you.

I don't blame you. That's a long winded post I laid up there....

I'll do wires AND another new set of plugs before anything else.

[mannydingo]

Hi, I have a fully working TB with IAC for sale in case that doesn't fix the problem either. I will send you a PM with my PayPal address should you decide to buy it.

[z5power]

I had a similiar issue on my 96. I just kept driving for a few days then the car went back to normal. I just figured water had gotten some places it shouldnt had, lol

[Pro]

I went ahead and put some new Duralast plug wires and a fresh set of Autolites in Thursday night, gapped @ .042. Reset the ECU as well.

SO FAR, ~60 miles and 3 heat cycles, the car's running like a top. It's the longest it's run without a CEL since the day I bought it.

I'll keep putting miles on it and see how it does.

I don't get how bad plug wires would cause a IAC DTC...

[mannydingo]

Maybe during the wire and plug installation you knocked something back into place. I would bet that what happened was that you hadn't plugged in one of the wires strong enough down onto a spark plug or down firm enough onto the distributor cap. It could have come loose with the pressure of the water. If the problem comes back then the problem is still there but the resetting of the ECU corrected it temporarily. That IAC code is strange for me also. Well, unless it's an intermittent problem with the IAC where it works most of the time and then goes bad for a while because of it no longer functioning correctly. I doubt it though and think your car will no longer have the problem.

[Pro]

unless it's an intermittent problem with the IAC

see, I feel like that could be the case. Well, I'll keep driving it and see what happens. I've got your number if the problem comes back and I need that TB.

thanks

[Pro]

I got a couple hundred miles on it now and it's still running very well.

just incase this thread is searched out some time down the road....

[vr4flyer]

I power washed my engine bay last year on my Vr4 twin turbo 3000 gt and i thought i killed my car. I live only 1 mile from the car wash that did it for me. My car died three or four times and ran like two or three plugs were not working. I had to leave for Vegas the next day! It dried out and ran great after a few hours. Thats the last time i do that!

[gybe]

Guys, no hard feelings but washing the engine with power washer is not a good idea. It's a quick and easy solution but in my whole lifetime always being around car repair techs and other people related to cars they have NEVER used a power washer. You just need plenty of time and a couple of cans of a good degreaser (TUV confirmed). If you plan to polish it after, that's up to you.

[vr4flyer]

good advice, thats what i am doing now, with good results.

[Pro]

I agree it's not a great idea. I've never had an issue before though. I'm pretty sure my problem came from my pulling the wires off shortly after washing it. They were the factory wires and I probably messed them up by moving them around after not being touched in years.

I did cut apart the stock wires to take a look. They suck ass.

Why it threw a DTC for IAC and not misfires I don't know.

I've power washed the engine bays of the past 8 cars I've owned including my GTO and 2 supercharged Grand Prixs with butt loads of electrical components under the hood, nothing ever got hurt.

[gybe]

You know the only problem is that the water will find the way. The water itself really doesn't have a problem reaching things through tiny holes and grooves. Also connectors on the harness are usually open on the backside and the plastic housing isn't enough to water seal the whole setup. So if a drop is captured between two terminals (or pins) of the connector, you'll get a short. And there are tons of other stuff that can go wrong. That's why I don't recommend it because you might launch several reactions, not just one. If a short circuit leap is at different voltages, like shorting 12V positive with any altered voltage can electronically damage anything that's in it's closest way. You can burn ECU or you can also burn the whole harness itself leaving you with nothing actually.