CEL Code P505 AFTER brand new ISC

[Faded95]

I recently installed a new ISC motor from DSMISC.com and the car ran fine for about a month before the CEL came on...same code P505 & the cars idle is now at about 1500 RPM from 900ish. I am going to check the O-ring to make sure it is seated properly, if that is not the problem my next step is to clean the tb, if it's not working at that point where else do I look?

 

[DSMlover2011]

Did you test your new ISC valve after the CEL came on? I know you said you just got it about a month ago but that doesn't mean it hasn't gone bad. There are several ways to check it. The quickest is to remove it from the throttle body while keeping it plugged in, cover up the opening where it bolts into the throttle body with a clean rag, have a friend start the car, and see if the ISC motor turns without any issues. I'm guessing you had bad luck and purchased a ISC that went bad right away.

 

[Faded95]

So I haven't had a chance to get into it but the car now is acting like it has a vacuum leak, so I'm pretty sure it's the o-ring at the isc. I'll finally have a chance to work on it tonight, hopefully it'll be a quick fix - I really doubt my brand new OE ISC motor went bad within one month.

I got to it last night, sure enough the o-ring was loose in the cavity with a very slight tear. I didn't have another new one so I decided to re-use it and it still is acting like it has a vacuum leak. I'm going to hook up a compressor over the weekend and test for leaks but I suspect it's coming from the damaged o-ring still. Nonetheless I cleared the P505 code just to see if it will come on again - it hasn't yet but I've only put about 5 miles on it.

Any insight?

 

[Faded95]

fixed the vacuum leak but the CEL came back on & it's got the classic DSM idle surge after a hot start. I had a mechanic friend look at it and he thinks it's a wiring problem and not an issue with the ISC itself. Plausible?

Also of note, I put a new (allbeit silghtly oversized) o-ring btw the ISC and TB and it is sealed tight.

 

[9!'clipseDOHC]

fixed the vacuum leak but the CEL came back on & it's got the classic DSM idle surge after a hot start. I had a mechanic friend look at it and he thinks it's a wiring problem and not an issue with the ISC itself. Plausible?

Also of note, I put a new (allbeit silghtly oversized) o-ring btw the ISC and TB and it is sealed tight.

Did you confirm that it is sealing correctly by doing a boost leak test? If not, do so. As you mentioned, it sounds like a boost leak. Did you change anything else when you did you ISC? If not I would still suspect your "slightly oversized" o-ring.

 

[Infamous33]

Don't forget to check for leaks on the other side of the throttle plate as well. If you sucked in intake gasket, the ecu will think the ISC can't control the idle correctly.
Are you showing good vacuum at idle? (In between surges, that is !!)

 

[Faded95]

Don't forget to check for leaks on the other side of the throttle plate as well. If you sucked in intake gasket, the ecu will think the ISC can't control the idle correctly.
Are you showing good vacuum at idle? (In between surges, that is !!)

I've got good vacuum at idle and boost holds at 16 psi at WOT so I don't suspect it's a boost leak anymore (my boost leak was coming from a broken vac line.) I actually have not done a boost leak test, when I was disconnecting my intake pipe to hook up the compressor I spotted the vacuum line so I fixed it and checked for vacuum & boost on my gauge.

The slightly oversized o-ring in question is from a package at a parts store, it's just a little thicker than the correct o-ring that I tore but the diameter is very close. I have thought about getting the correct o-ring from the dealer or an online source but I'd like to be a little more confident about the problem before I spend more money.

 

[bryanwheat]

The car will still hold boost with a minor leak just fine. The turbo will just be working a little harder to achieve that psi. Because of the way the wastegate works, the turbo will keep spinning faster and faster until the wastegate opens. So because of that if there is a leak the turbo will as fast as is has to to achieve the pressure to open the wastegate. The pressure will register the same on the gauge, but the actual airflow will be higher.

 

[9!'clipseDOHC]

The car will still hold boost with a minor leak just fine. The turbo will just be working a little harder to achieve that psi. Because of the way the wastegate works, the turbo will keep spinning faster and faster until the wastegate opens. So because of that if there is a leak the turbo will as fast as is has to to achieve the pressure to open the wastegate. The pressure will register the same on the gauge, but the actual airflow will be higher.

Exactly! OP, this is why you need to do a boost leak test. You said you want to be "a little more confident about the problem before spending money", a boost leak test will tell you if it is sealing and it will also tell you if you have any other boost leaks causing your idle issues. There are lots of reasons to do a boost leak test. Just do it.

 

[Faded95]

Thanks for the input - I've been working on naturally aspirated cars for a long time but I'm definately a bit of a newbie to forced induction. I figured that when I was reading good vacuum and boost at the gauge I had fixed the problem and the idle was a different problem alltogether. I'll do a boost leak test to see if I have a minor leak at the isc (or elswhere). I do appreciate the comments, it's always a good day to learn something!

 

[Faded95]

So - did a boost leak test last night, I've got a couple of gaskets to replace but the ISC isn't leaking. Both my TB to TB elbow gasket and my turbo to j-pipe gasket are leaking, my 1G bov is also leaking slightly. checked vac lines, IC pipes, and the intake manifold gasket and all seemed to be sealed well. I'm going to replace the two gaskets and re-check for leaks.

 

[92AWDHX40]

Sounds good, blt always help me out, so many lack to do it, so simple to help issues.

 

[21_Eclipse]

To op
What kind of code reader do you use? And can i use it on my 95 RS?

 

[Faded95]

To op
What kind of code reader do you use? And can i use it on my 95 RS?

Most parts stores have diagnostic code readers and they'll check the codes for you.

 

[Faded95]

I installed new gaskets and patched up the leaky j-pipe a couple of weekends back and the car seems to idle right after a weeks worth of commuting. Also noticed boost peak up 2 psi higher than before I fixed the leaks...time to dial back the boost controller, no need to starve my stock fuel system.

 

[Faded95]

It's been awhile since I last updated this thread. Not long after the last post the CEL came back on and it would sometimes surge and the idle would creep up. I thought it could be bad capacitors in my ECU, so I pulled it and checked it out but that wasn't it, just in case I swapped in another ECU with the same results. Over time the problem dimished or I just got used to it, it wasn't surging as much though.

Fast forward to last week, time to get an emissions test (they're required every other year here), and it failed for high NOx. I understand that high NOx means lean mix or high pressures/temperatures in the cc, it can be a boost leak, bad EGR, clogged injectors, etc. So over the weekend I started with a boost leak test, fixed the leaks and then moved on. Next I took off the throttle body and cleaned it out, then the EGR came off and I cleaned it out and cleaned out the EGR ports on the intake manifold. I also replaced the BISS o-ring and ISC o-ring. I finished and buttoned everything back up and did another BLT with good results so I was satisfied but I didn't have time for a test drive so just a start-up instead.

Monday morning on the way to work the idle was back up to 1500 rpm's and when I drove it again at lunchtime the surge had returned. I was frustrated and again wanted to drive my car into a brick wall (I'm sure a common feeling for DSM owners) but I figured I still needed to adjust my BISS and see if I could get it working right. Over my lunch hour today I adjusted the BISS with the car running and ISC still plugged in. I've read that you're supposed to unplug the ISC and also ground out some relays but the engine bay was too hot to do that so I rolled the deis and just turned the screw. The idle responded to the BISS but I figured it wouldn't stay because I didn't follow the procedures I'd read about.

On my way back to work, the idle held steady with no creep or surge even through two stop and go construction zones. My CEL is still on but I'll reset that when I get home tonight and see if it comes back. I'm hoping I've finally got my P0505 fixed and that I can pass emissions this week too!