SES light went off today. Pulled the codes as soon as I got to work and my reader showed me 2 codes: P1590- Rough road signal/ABS fault and a code for my rear O2 sensor (bank 2 sensor 2). I also noticed some hesitation when accelerating from 35-45 mph (about 2200-2600 rpm), feels like a slight misfire. It is very slight, almost imperceptable, but its there when I lean on the gas very lightly and try to accelerate. Could the codes and the misfire be related? I just changed plugs and wires, checked all the seats and made sure the plugs are torqued and wired to the appropriate cylinders. I'm thinking the misfire might be a small vacuum leak. I looked at the vacuum diagram under the bonnet, but I can't read the whole thing, as it looks like a dog chewed it. Can someone post a pic of the vacuum diagram, or a pic of the engine showing the vacuum lines? Any ideas as to what would throw a P1590 code? I do not have ACE, and all the old posts on here regarding P1590 are related to ACE. Thanks in advance.

 

Eagle: I had the same thing a few wekks ago on my 2003 D2. I chose the same route as you plugs, and wires with no luck in fixing the apparent misfire symptoms.

I then took off the Idle Air control Valve and cleaned it and performed the Seafoam Induction Cleaning. One smoke show later, the misfire was gone.

 

I also just did the IACV cleaning. My plunger was stuck half way open, and I couldn't move it, not even with a screwdriver. After 3 cans of carb cleaner, a lot of banging, and some words I wouldn't say in front of my mother, I got it cleaned and moving freely. I don't think its the IACV. But I'll check it again tonight to make sure it didn't stick again.

 

You may have damaged the 200 position stepper motor, usually not a good idea to force the pintle.

 

Any way to check to see if the motor is working? I'd rather not start throwing parts blindly at this thing. I had a code for the IACV right before I cleaned it, along with a real rough idle, and now the code has been gone for about 500 miles, and the idle is fine.

 

Then you should have bought a lottery ticket. When you have them removed, and turn key to position 2, the plunger should move slightly.

 

I'll check it tonight and report back. In the meantime, anyone have a pic of the vacuum lines so I can check them. Will the IACV throw a P1590 code? Doesn't seem likely.

 

just a thought... when I bought mine, same year same miles it was misfiring and idling unevenly... I told the dealer Id take possession if they fix this and it turned out to be one of the coil packs... I had them put both new coil packs and wires and plugs in... it smoothed right out... since then I have learned allot here and had a stack of other codes to go through and now have gotten rid of them...

 

First, a 1590 is for your 3 amigos. What are the exact fault code numbers only. You should not be messing with your idle solenoid, most people usually break a perfectly good part when they start mess with it, besides it won't cause a misfire. Is it working, this is not rocket science, you your engine starts and idles, it is working, if not it is bad.
Have you replace your 02's yet?
By the way, whos plugs and wires did you install?

 

I have not replaced the o2 sensors yet. I have found in the past that just because the OBDII shows an o2 code does not mean the o2s are bad, but just the sympton of another problem with the car. I will look into replacing the o2s, but before I drop $250 on them, I want to look at other possibilities. I refuse to just throw parts at a car and hope it fixes it.

Before cleaning the IACV (about 400 miles ago), the car would not idle on cold start. It would start very weakly, and fluctuate wildly between 200 rpm and 700 rpm on startup, sometimes stalling out. After cleaning the IACV, the car roars to life when I turn the ignition, and idles around 1300 on startup, then after 10 seconds drops to 1000, then another 20-30 seconds, it'll drop again to 750 rpm or so. Now, 400 miles later, my idle has gotten a bit rougher, and I feel this very slight misfire. When i punch the gas, the truck accelerates fine, its just when I slightly press the accelerator between 32-45 mph do I feel the misfire. On sport mode, I don't really feel the misfire.

The check engine light will also go out for about 60-120 miles every once in a while (1-2 ECU cycles), then come on for about 200 miles, then go out again, then come on again. Further, this P1590 is real bugger. As you mentioned, Mike, this usually has something to do with the three amigos, but I don't have ACE (yes I am positive I don't have it). I am completely mistified. Further, I went back and checked all my old service records (I keep every receipt for my truck, including gas, oil, fluids, etc) I noticed the code had appeared when I had my tranny replaced at 75,000 miles (it was mentioned in the shops diagnosis). That was 4 years ago.

I am so mystified by all this, I'm thinking it's probably a vacuum leak somewhere. Those pesky little leaks can really be a problem sometimes. Thanks so much guys, and Happy Easter/Passover