I had the same Problem did pretty much every thing you did n wasted alot money. turned out that when they replaced the engine before i bought my car they scraped off a small peice of insulation on the wires going into the TPS so they were grounding out. And though it DID NOT throw a code my idle air control valve was bad causing a vacuum leak wich causes hotter combustion temp = fouling plug. (what I was told) replaced that and fixed the wires and no more codes..... I also had a few grounding wires that were lose..... AS DTN said you might want to check after dark and spray your wires. because after i put NGK plugs and MSD wires still had some mad arching. hope that helps

 

DTN, thanks for the checklist it was really convenient but unfortunately it looks like most everything on there has either been checked or replaced. As far as codes, no there isn't any codes for sensors that popped up. Just the misfire code, which I thought was wierd. Anyway here's some answers to that checklist.

b. Checked resistance on the sensor and got 847 ohms with the key off. Not sure if this is within specs but seems good to me. Took it out and cleaned it also.
c. It's a good possibility but don't know how to check/adjust it. Any advice would be appreciated.
d. Already performed a compression test and compression is good across all 4 cylinders. No leaks. Leak down test was also conducted and there was no sign of any leaking intake or exhaust valves.
e. It's been taken out already and checked. Resistance checked out ok when cold and decreased in resistance when heated up.
f. No teeth missing.
h. ECM has already been replaced when I put in the new engine harness.

JC,
Nice to see someone else had the same problem lol. I was beginning to think I was the only one....Do you have any info on where the idle air control valve is located and how to check them? I already checked for vacuum leaks and don't have any but it wouldn't hurt to check the valve. I am going to do the spray test tonight when it gets darker and go through all my wires and check for breaks. Thanks for your help.

 

.a.Ignition system related part(s) failed
b.Poor crankshaft position sensor signal troubleshooting http://hmaservice.com/data/Passenger/HY/HM...G/ef89556b1.gif
c.Incorrect air/fuel ratio verify correct MAF direction by arrow, get codes read, lots of other things on this... improper fuel injectors, fuel pressure, vacuum leak
d.Low compression pressure
e.Engine coolant temperature sensor failed
f.Timing belt missing teeth has timing been set?
g.Injector failed
h.Engine control module failed possible

And you're sure there are NO other codes being thrown by the engine accompanying this P0304? Something like this should have other codes. If there are other codes then we're troubleshooting a symptom instead of the problem. Like going to the doctor and saying "I have a runny nose" when you've got the flu. It would be a good idea to get the codes re-read.

 

That's what I thought. But there are absolutely NO other codes..I've had it checked about 4 times now by autozone and once when it went to the dealership and it keeps coming back just P0304.

b. The sensor reading I got was 847 ohms at like regular air temp when the block was stone cold. It says 486 -594 in the link at 68 degrees? So think is good right? Resistance drops with increase in temperature.

c. MAF is on the right way. fuel injectors are stock. fuel pressure good. and no vacuum leaks.

f. Timing has been set.

 

ok...
CKP sensor = RPM sensor. Is your RPM gauge moving properly? Also, you should really check it at 70 or so degrees. I don't think it would change that much. It may be out of tollerance and not providing the ECU a clean signal.




some other A/F checks- Check fuel injectors for obstructions. run the MAF to open air instead of to the box. Check the purge valve for ticking. Remove the heat shield from the exhaust and check using a mirror for cracks on the cylinders, THOROUGHLY, they can be small and there is a recall on them if they crack.

.a.Ignition system related part(s) failed
b.Poor crankshaft position sensor signal troubleshooting http://hmaservice.com/data/Passenger/HY/HM...G/ef89556b1.gif
c.Incorrect air/fuel ratio verify correct MAF direction by arrow, get codes read, lots of other things on this... improper fuel injectors, fuel pressure, vacuum leak
d.Low compression pressure
e.Engine coolant temperature sensor failed
f.Timing belt missing teeth
g.Injector failed
h.Engine control module failed

Another thing, since this is a P0304 meaning a misfire on cyl 4, try to check inside the intake manifold for obstructions or around the intake manifold for cracks, maybe even a missing grommet on the fuel injector.

 

http://viewmorepics.myspace.com/index.cfm?...mageID=40593159

I dont know how to check it but mine was obviously bad it was sucking the vacuum line shut between the intake and the valve and when i took it off it rattled like there was something broke inside. there pretty expensive new about $250 I got mine at a junk yard. think was like $50 or $60 but was hard to find!! I unpluged mine and it helped with the arching. and before some one ask I DID NOT have any idle problems except when it would rev down it would hold around 2,000 Rpm for a sec.

If the pic dosn't work I can e-mail it to you just pm me where

 

Oh ok now I understand. It's actually called the Idle Speed Control Actuator. I was confused when you talked about it earlier because I thought you meant a little check valve with an adjustment or something on the intake. But I don't think mine's bad. Resistance checked out ok and the car doesn't even run after you unplug it so it should be operating properly. Thanks for the info.

DTN, the RPM gauge does in fact work properly. I'm going to go through all the checks again tonight sometime but it will probably take me until tomorrow to get it all done. I'll let you know what I find out so I can get you some accurate answers to your questions and maybe I'll find something new I've overlooked...

 

Are you talking about the electrical connection, or the vacuum line to the IAC? If you're talking about the electrical connection, set the idle so that it is the same with or without the IAC plugged in. It sits at 1/4 open on a spring both ways and is controlled by the computer. unplug it, set the idle, plug it in, wait for the rpms to drop, unplug it and see if the RPMs change. Your car should not die when you disconnect the IAC. This could possibly be your problem. The car should die with the IAC vacuum line disconnected.

 

Sorry about the The wrong term. Hope the Info helps

 

If nothing else, try tapping the IAC (idle speed motor, whatever) with a screwdriver or hammer. I had one idle bad and tapping it would make it idle just fine.

However I dont think that would give you that code. How is the air filter? I think if it were sensor related you would be more likely to have multiple codes, not just one cylinder. At least maybe a random misfire code.

If you clear the code, when does the light come back on or flash? Cruising, WOT, right at idle? And does it come back as P0304 everytime?

Im thinking maybe a vacuum leak? Have you sprayed the lines with brakleen (CAREFULLY!) or anything. What if you swap two injectors?